W3C

SMIL Animation

W3C Working Draft 28-January-2000

This version:
http://www.w3.org/TR/2000/WD-smil-animation-20000128
Latest version:
http://www.w3.org/TR/smil-animation
Previous version:
http://www.w3.org/TR/1999/WD-smil-animation-19991029
Editor(s)
Patrick Schmitz (pschmitz@microsoft.com), Microsoft
Aaron Cohen (aaron.m.cohen@intel.com), Intel


Abstract

This is a working draft of a specification of animation functionality for XML documents.  It describes an animation framework as well as a set of base XML animation elements suitable for integration with XML documents. It is based upon the SMIL 1.0 timing model, with some extensions.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.

This is the "Last Call Working Draft" of the specification for SMIL Animation. The Last Call review period ends at 2359Z on 27 February 2000. Please send review comments before the review period ends to www-smil@w3.org.

If the review indicates that there is consensus in the community, the Working Group plans to ask the W3C Director to advance this document to Candidate Recommendation.

This Working Draft has been produced as part of the W3C Synchronized Multimedia Activity. The document has been written by the SYMM Working Group (members only) working with the SVG Working Group (members only). The goals of the SYMM group are discussed in the SYMM Working Group charter (members only).

This is a W3C Working Draft for review by W3C Members and other interested parties. It is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress". This document is work in progress and does not imply endorsement by the W3C membership.

A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.


Quick Table of Contents

1. Introduction
2. Overview and terminology
3. Animation model
4. Animation elements
5. Integrating SMIL Animation into a host language
6. Document Object Model support
7. Appendix: Differences from SMIL 1.0 timing model
8. References


Full Table of Contents

1. Introduction

2. Overview and terminology
    2.1. Basics of animation
    2.2. Animation function values
    2.3. Symbols used in the semantic descriptions

3. Animation model
    3.1. Specifying the animation target
    3.2. Specifying the animation function f(t)
        3.2.1. Animation function timing
        3.2.2. Animation function values
        3.2.3. Animation function calculation modes
    3.3. Specifying the animation effect F(t)
       3.3.1. Repeating animation
       3.3.2. Controlling the active duration
       3.3.3. Computing the active duration
       3.3.4. Freezing animations
       3.3.5. Additive animation
       3.3.6. Restarting animations
    3.4. Handling syntax errors
    3.5. The animation sandwich model
    3.6. State transition model
    3.7. Timing model details
       3.7.1. Timing and real-world clock times
       3.7.2. Interval timing
       3.7.3. Unifying event-based and scheduled timing
       3.7.4. Hyperlinks and timing
       3.7.5. Propagating changes to times
    3.8. Animation function value details
    3.9. Common syntax DTD definitions

4. Animation elements
    4.1. The animate element
    4.2. The set element
    4.3. The animateMotion element
    4.4. The animateColor element

5. Integrating SMIL Animation into a host language
    5.1. Required host language definitions
    5.2. Required definitions and constraints on animation targets
    5.3. Constraints on manipulating animation elements
    5.4. Required definitions and constraints on element timing
    5.5. Error handling semantics
    5.6. SMIL Animation namespace

6. Document Object Model support
    6.1. Event model
    6.2. Supported interfaces
    6.3. IDL definition
    6.4. Java language binding
    6.5. ECMAScript language binding

7. Appendix: Differences from SMIL 1.0 timing model

8. References


1. Introduction

This document describes a framework for incorporating animation onto a time line and a mechanism for composing the effects of multiple animations.  A set of basic animation elements are also described that can be applied to any XML-based language. A language with which this module is integrated is referred to as a host language. A document containing animation elements is referred to as a host document.

Animation is inherently time-based. SMIL Animation is defined in terms of the SMIL timing model.  The animation capabilities are described by new elements with associated attributes and semantics, as well as the SMIL timing attributes. Animation is modeled as a function that changes the presented value of a specific attribute over time.

The timing model is based upon SMIL 1.0, with some changes and extensions to support interactive (event-based) timing. SMIL Animation uses a simplified "flat" timing model, with no time containers (like <par> or <seq>). This version of SMIL Animation may not be used with documents that otherwise contain timing. See also Required definitions and constraints on element timing.

While this document defines a base set of animation capabilities, it is assumed that host languages may build upon the support to define additional and/or more specialized animation elements.  In order to ensure a consistent model for document authors and runtime implementers, we introduce a framework for integrating animation with the SMIL timing model. Animation only manipulates attributes and properties of the target elements, and so does not require any specific knowledge of the target element semantics.

The examples in this document that include syntax for a host language use SMIL, SVG, XHTML and CSS. These are provided as an indication of possible integrations with various host languages.

2. Overview and terminology

2.1. Basics of animation

Animation is defined as a time-based manipulation of a target element (or more specifically of some attribute of the target element, the target attribute). The animation defines a mapping of time to values for the target attribute. This mapping accounts for all aspects of timing, as well as animation-specific semantics. 

Animations specify a begin, and a simple duration that can be repeated. Each animation defines an animation function that produces a value for the target attribute, for any time within the simple duration. The author can specify how long or how many times an animation function should repeat. The simple duration combined with any repeating behavior defines the active duration.

The target attribute is the name of a feature of a target element as defined in a host language document. This may be (e.g.) an XML attribute contained in the element or a CSS property that applies to the element.  By default, the target element of an animation will be the parent of the animation element (an animation element is typically a child of the target element). However, the target may be any element in the document, identified either by an ID reference or via an XLink [XLink] locator reference.

When an animation is running, it does not actually change the attribute values in the DOM [DOM-Level-2].  The animation runtime must maintain a presentation value for each animated attribute, separate from the DOM or CSS Object Model (OM). If an implementation does not support an object model, it must maintain the original value as defined by the document as well as the presentation value. The presentation value is reflected in the display form of the document. Animations thus manipulate the presentation value, and do not affect the base value exposed by DOM or CSS OM. 

The animation function is evaluated as needed over time by the implementation, and the resulting values are applied to the presentation value for the target attribute. Animation functions are continuous in time and can be sampled at whatever frame rate is appropriate for the rendering system. The syntactic representation of the animation function is independent of this model, and may be described in a variety of ways. The animation elements in this specification support syntax for a set of discrete or interpolated values, a path syntax for motion based upon SVG paths, keyframe based timing, evenly paced interpolation, and variants on these features. Animation functions could be defined that were purely or partially algorithmic (e.g. a random value function or a motion animation that tracks the mouse position) . In all cases, the animation exposes this as a function of time.

The presentation value reflects the effect of the animation upon the base value. The effect is the change to the value of the target attribute at any given time. When an animation completes, the effect of the animation is no longer applied, and the presentation value reverts to the base value by default. The animation effect can also be extended to freeze the last value for the remainder of the document duration.

Animations can be defined to either override or add to the base value of an attribute. In this context, the base value may be the DOM value, or the result of other animations that also target the same attribute. This more general concept of a base value is termed the underlying value. Animations that add to the underlying value are described as additive animations. Animations that override the underlying value are referred to as non-additive animations.

As a simple example, the following defines an animation of an SVG rectangle shape.  The rectangle will change from being tall and thin to being short and wide.

<rect ...>
   <animate attributeName="width"  from="10px"  to="100px" 
            begin="0s" dur="10s" />
   <animate attributeName="height" from="100px" to="10px"
            begin="0s" dur="10s" />
</rect>

The rectangle begins with a width of 10 pixels and increases to a width of 100 pixels over the course of 10 seconds. Over the same ten seconds, the height of the rectangle changes from 100 pixels to 10 pixels.

2.2. Animation function values

Many animations specify the animation function f(t) as a sequence of values to be applied over time. For some types of attributes (e.g. numbers), it is also possible to describe an interpolation function between values.

As a simple form of describing the values, animation elements can specify a from value and a to value. If the attribute takes values that support interpolation (e.g. a number), the animation function can interpolate values in the range defined by  from and to, over the course of the simple duration. A variant on this uses a by value in place of the to value, to indicate an additive change to the attribute.

More complex forms specify a list of values, or even a path description for motion. Authors can also control the timing of the values, to describe "keyframe" animations, and even more complex functions.

2.3. Symbols used in the semantic descriptions

f(t)
The simple animation function that maps times within the simple duration to values for the target attribute (0 <= t <= simple duration). Note that while F(t) defines the mapping for the entire animation, f(t) has a simplified model that just handles the simple duration.
F(t)
The effect of an animation for any point in the animation. This maps any non-negative time to a value for the target attribute. A time value of 0 corresponds to the time at which the animation begins. Note that F(t) combines the animation function f(t) with all the other aspects of animation and timing controls.
B
The begin of an animation.
d
The simple duration of an animation.
AD
The active duration of an animation. This is the period during which time is actively advancing for the animation. This includes any effect of repeating the simple duration, but does not include the time during which the animation may be frozen.
AE
The active end. This is the end of the active duration of an animation.

3. Animation model

This section describes the attribute syntax and semantics for describing animations. The specific elements are not described here, but rather the common concepts and syntax that comprise the model for animation.  Document issues are described, as well as the means to target an element for animation. The animation model is then defined by building up from the simplest to the most complex concepts: first the simple duration and animation function f(t), and then the overall behavior F(t).  Finally, the model for combining animations is presented, and additional details of animation timing are described.

The time model depends upon several definitions for the host document: A host document is presented over a certain time interval. The start of the interval in which the document is presented is referred to as the document begin. The end of the interval in which the document is presented is referred to as the document end. The difference between the end and the begin is referred to as the document duration. The formal definitions of presentation and document begin and end are left to the host language designer (see also Required host language definitions).

3.1. Specifying the animation target

The animation target is defined as a specific attribute of a particular element. The means of specifying the target attribute and the target element are detailed in this section.

The Target attribute

The target attribute to be animated is specified with attributeName. The value of this attribute is a string that specifies the name of the target attribute, as defined in the host language.

The attributes of an element that can be animated are often defined by different languages, and/or in different namespaces. For example, in many XML applications, the position of an element (which is a typical target attribute) is defined as a CSS property rather than as XML attributes. In some cases, the same attribute name is associated with attributes or properties in more than one language, or namespace.  To allow the author to disambiguate the name mapping, an additional attribute attributeType is provided that specifies the intended namespace. 

The attributeType attribute is optional. By default, the animation runtime will resolve the names according to the following rule: If there is a name conflict and attributeType is not specified, the CSS namespace is matched first (if CSS is supported in the host language), followed by the default namespace for the target element. 

If a target attribute is defined in an XML Namespace other than the default namespace for the target element, the author must specify the namespace of the target attribute using the associated namespace prefix as defined in the scope of the target element. The prefix is prepended to the value for attributeName.

For more information on XML namespaces, see [XML-NS].

attributeName = <attributeName>
Specifies the name of the target attribute. An XMLNS prefix may be used to indicate the XML namespace for the attribute. The prefix will be interpreted in the scope of the target element.
 
attributeType = "CSS | XML | auto"
Specifies the namespace in which the target attribute and its associated values are defined. The attribute value is one of the following (values are case-sensitive):
"CSS"
This specifies that the value of "attributeName" is the name of a CSS property, as defined for the host document. This argument value is only meaningful in host language environments that support CSS.
"XML"
This specifies that the value of "attributeName" is the name of an XML attribute defined in the default XML namespace for the target element. If the value for attributeName has an XMLNS prefix, the implementation must use the associated namespace as defined in the scope of the target element.
"auto"
The implementation should match the attributeName to an attribute for the target element. The implementation must first search through the CSS namespace for a matching property name, and if none is found, search the XML namespace.
This is the default.

The Target element

An animation element can define the target element of the animation either explicitly or implicitly. An explicit definition uses an attribute to specify the target element. The syntax for this is described below.

If no explicit target is specified, the implicit target element is the parent element of the animation element in the document tree. It is expected that the common case will be that an animation element is declared as a child of the element to be animated. In this case, no explicit target need be specified.

If an explicit target element reference cannot be resolved (e.g. no such element can be found), the animation has no effect. In addition, if the target element (either implicit or explicit) does not support the specified target attribute, the animation has no effect. See also Handling syntax errors.

The following two attributes can be used to identify the target element explicitly:

targetElement = "<IDREF>"
This attribute specifies the target element to be animated. The attribute value must be the value of an XML identifier attribute of an element within the host document. For a formal definition of "IDREF", refer to XML 1.0 [XML]. 
href = uri-reference
This attribute specifies an XLink locator, referring to the target element to be animated.

When integrating animation elements into the host language, the language designer should avoid including both of these attributes. If however, both attributes must be included in the host language, and they both occur in an animation element, the XLink "href" attribute takes precedence over the "targetElement" attribute.

The advantage of using a "targetElement" attribute is the simpler syntax of the attribute value compared to the "href" attribute. The advantage of using the XLink "href" attribute is that it is extensible to a full linking mechanism in future versions of SMIL Animation, and the animation element can be processed by generic XLink processors. The XLink form is also provided for host languages that are designed to use XLink for all such references. The following two examples illustrate the two approaches.

This example uses the simpler targetElement syntax:

<animate targetElement="foo" attribute="bar" .../>

This example uses the more flexible XLink locater syntax, with the equivalent target.

<animate href="#foo" attribute="bar" .../>

When using an XLink "href" attribute on an animation element, the following additional XLink attributes need to be defined in the host language. These may be defined in a DTD, or the host language may require these in the document syntax to support generic XLink processors. For more information, refer to the "XML Linking Language (XLink)" [XLink].

The following XLink attributes are required by the XLink specification. The values are fixed, and so may be specified as such in a DTD. All other XLink attributes are optional, and do not affect SMIL Animation semantics.

type = 'simple'
Identifies the type of XLink being used. To link to the target element, a simple link is used, and thus the attribute value is fixed to "simple". 
actuate = 'onLoad'
Indicates that the link to the target element is followed automatically (i.e., without user action).
show = 'embed'
Indicates that the reference does not include additional content in the file. 

Additional details on the target element specification as relates to the host document and language are described in Required definitions and constraints on animation targets.

3.2. Specifying the animation function f(t)

Every animation function defines the value of the attribute at a particular moment in time. The time range for which the animation function is defined is the simple duration. The animation function does not produce defined results for times outside the range of 0 to the simple duration.

3.2.1. Animation function timing

The basic timing for an element is described using the begin and dur attributes. Authors can specify the begin time of an animation in a variety of ways, ranging from simple clock times to the time that an event like a mouse-click happens. The length of the simple duration is specified using the dur attribute. The attribute syntax is described below. The normative syntax rules for each attribute value variant are described below (in Timing Attribute Values); a syntax summary is provided here as an aid to the reader.

begin
Defines when the element should begin (i.e. become active).
The attribute value can be one of the following types of values:
clock-value
Specifies the presentation time at which the animation begins. The begin is thus defined relative to the document begin.
syncbase-value : ( id-ref "." ) ( "begin" | "end" ) ( "+"clock-value )?
Describes a syncbase and an offset from that syncbase. The element begin is defined relative to the begin B or active end AE of another animation.
event-value : ( id-ref "." )? ( event-ref  ) ( "+"clock-value )?
Describes an event and an optional offset that determine the element begin. The animation begin is defined relative to the time that the event is raised. Events may be any event defined for the host language in accordance with [DOM2Events]. These may include user-interface events, event-triggers transmitted via a network, etc. Details of event-based timing are described in the section below on Unifying event-based and scheduled timing.
"indefinite"
The begin of the animation will be determined by a "beginElement()" method call or a hyperlink targeted to the animation element.
The SMIL Animation DOM methods are described in the Supported methods section.
Hyperlink-based timing is described in the Hyperlinks and timing section.
dur
Specifies the simple duration.
The attribute value can be one of the following types of values:
clock-value
Specifies the length of the simple duration in presentation time.
Value must be greater than 0.
"indefinite"
Specifies the simple duration d as indefinite.

If no begin is specified, the default value is "0" - the animation begins when the document begins. If there is any error in the argument value syntax for begin, the default value for begin will be used.

If the animation does not have a dur attribute, the simple duration is indefinite. Note that interpolation will not work if the simple duration is indefinite. See also Interpolation and indefinite simple durations.

If there is any error in the argument value syntax for dur, the attribute will be ignored (as though it were not specified), and so the simple duration will be indefinite.

If the begin is specified to be "indefinite" or specifies an event-base, the time of the begin is not actually known until the element is activated (e.g. with a hyperlink, DOM method call or the referenced event). The time is referred to as unresolved when it is not known. At the point at which the element begin is activated, the time becomes resolved. This is described in detail in Unifying event-based and scheduled timing.

Timing attribute values

In the syntax specifications that follow, allowed white space is indicated as "S", defined as follows (taken from the [XML] definition for "S"):

S ::= (#x20 | #x9 | #xD | #xA)+
Clock values

Clock values have the following syntax:

Clock-val         ::= Full-clock-val | Partial-clock-val 
                      | Timecount-val
Full-clock-val    ::= Hours ":" Minutes ":" Seconds ("." Fraction)?
Partial-clock-val ::= Minutes ":" Seconds ("." Fraction)?
Timecount-val     ::= Timecount ("." Fraction)? (Metric)?
Metric            ::= "h" | "min" | "s" | "ms"
Hours             ::= DIGIT+; any positive number
Minutes           ::= 2DIGIT; range from 00 to 59
Seconds           ::= 2DIGIT; range from 00 to 59
Fraction          ::= DIGIT+
Timecount         ::= DIGIT+
2DIGIT            ::= DIGIT DIGIT
DIGIT             ::= [0-9]

For Timecount values, the default metric suffix is "s" (for seconds). No embedded white space is allowed in clock values, nor is leading or trailing white space.

In SMIL Animation, clock values describe presentation time. Presentation time behaves like the timecode shown on a counter of a tape-deck that advances at the speed of the presentation. It reflects that the presentation can be stopped, and that its speed can be decreased or increased either by user actions, or by the animation engine itself.

The following are examples of legal clock values:

Fractional values are just (base 10) floating point definitions of seconds. Thus:

00.5s = 500 milliseconds
00:00.005 = 5 milliseconds

Syncbase values

A syncbase value has the following syntax:

 Syncbase-value   ::= ( Syncbase-element "." Time-symbol )
                      ( S "+" S Clock-value )? 
 Syncbase-element ::= Id-value
 Time-symbol      ::= "begin" | "end"

A syncbase value starts with a Syncbase-element term defining the value of the id attribute of an animation element referred to as the syncbase element. This element must be another animation element contained in the host document. For a formal definition of "ID", refer to XML 1.0 [XML]. 

The syncbase element is qualified with one of the following time symbols:

begin
Denotes the begin time of the syncbase element.
end
Denotes the Active End AE of the syncbase element.

The time symbol can be followed by a clock value. The clock value specifies a presentation time offset from the time (i.e. the begin or end) specified by the syncbase and time symbol. If the clock value is omitted, it defaults to "0".

No embedded white space is allowed between a syncbase element and a time-symbol. White space will be ignored before and after a "+" for a clock value. Leading and trailing white space (i.e. before and after the entire syncbase value) is not allowed.

Examples:

  begin="x.end+45s"    : Begin 45 seconds after "x" ends
  begin="x.begin"      : Begin when "x" begins
  begin="x.begin + 1m" : Begin 1 minute after "x" begins

Event values

An event value has the following syntax:

  Event-value       ::= ( Eventbase-element "." )? Event-symbol 
                        ( S "+" S Clock-value )? 
  Eventbase-element ::= Id-value

An Event value starts with the id value of the event-base element. The event-base element is the element on which the event is observed. Given DOM event bubbling, the event-base element may be either the element that raised the event, or it may be an ancestor element on which the bubbled event can be observed. Refer to DOM-Level2-Events [DOM2Events] for details.
The "Id-value" is the value of an attribute declared to be of type ID (per the XML definition) in the host language, for the event-base element. This element must be another element contained in the host document.

If the id value term is missing, the event-base element is defined to be the target element of the animation. 

The event value must specify an Event-symbol. This term specifies the name of the event that is raised on the Event-base element.  The host language designer must specify which event names can be used.

The last term specifies an optional clock-value that is a presentation time offset from the event. If this term is omitted, the offset is 0.

No embedded white space is allowed between an eventbase element and an event-symbol. White space will be ignored before and after a "+" for a clock value. Leading and trailing white space (i.e. before and after the entire eventbase value) is not allowed.

Note that it is not considered an error to specify an event that cannot be raised on the Event-base element (such as click for audio or other non-visual elements).  Similarly, if the host language allows dynamically created events (as supported by DOM-Level2-Events [DOM2Events]), and it is not possible to specify all Event-symbol names, unrecognized names may not be considered errors. Host language specifications must include a description of legal event names, and/or allow any name to be used.

Examples:

 begin="x.load"     : Begin when "load" is raised on "x"
 begin="x.focus+3s" : Begin 3 seconds after a "focus" event is raised on "x"

The defaults for the event and target element syntax make it easy to define simple interactive behavior. The following example sets the rect element color to be red for 5 seconds, after the user clicks on the element.

  <rect ...>
    <set begin="click" dur="5s" to="red"
         attributeName="fill" attributeType="CSS" />
    ...
  </rect>

 

3.2.2. Animation function values

The animation is described either as a list of values, or in a simplified form that describes the from, to and by values.

from = "<value>"
Specifies the starting value of the animation.
to = "<value>"
Specifies the ending value of the animation.
by = "<value>"
Specifies a relative offset value for the animation.
values = "<list>"
A semicolon-separated list of one or more values. Vector-valued attributes are supported using the vector syntax of the attributeType domain.

The animation values specified in the animation element must be legal values for the specified attribute. See also Animation function value details

Leading and trailing white space, and white space before and after semi-colon separators, will be ignored.

If any values are not legal, the animation will have no effect (see also Handling Syntax Errors).

If a list of values is used, the animation will apply the values in order over the course of the animation (pacing and interpolation between these values is described in the next section). If a list of values is specified, any from, to and by attribute values are ignored.

The simpler from/to/by syntax provides for several variants. Note that from is optional, but that one of by or to must be used (unless of course a list of values is provided). It is not legal to specify both by and to attributes - if both are specified, only the to attribute will be used (the by will be ignored). The combinations of attributes yield the following classes of animation:

from-to animation
Specifying a from value and a to value defines a simple animation, equivalent to a values list with 2 values. The animation function is defined to start with the from value, and to finish with the to value.
from-by animation
Specifying a from value and a by value defines a simple animation in which the animation function is defined to start with the from value, and to change this over the course of the simple duration d by a delta specified with the by attribute. This may only be used with attributes that support addition (e.g. most numeric attributes).
by animation
Specifying only a by value defines a simple animation in which the animation function is defined to offset the underlying value for the attribute, using a delta that varies over the course of the simple duration d, starting from a delta of 0 and ending with the delta specified with the by attribute. This may only be used with attributes that support addition.
to animation
This describes an animation in which the animation function is defined to start with the underlying value for the attribute, and finish with the value specified with the to attribute. Using this form, an author can describe an animation that will start with whatever value the attribute has originally, and will end up at the desired to value.

The last two forms "by animation" and "to animation" have additional semantic constraints when combined with other animations. The details of this are described below in the section How from, to and by attributes affect additive behavior.

Interpolation and indefinite simple durations

If the simple duration of an animation is indefinite (e.g. if no dur value is specified), interpolation is not generally meaningful. While it is possible to define an animation function that is not based upon a defined simple duration (e.g. some random number algorithm), most animations define the function in terms of the simple duration. If an animation function is defined in terms of the simple duration and the simple duration is indefinite, the first value of the animation function (i.e. f(0)) should be used (effectively as a constant) for the animation function.

Examples

The following example using the values syntax animates the width of an SVG shape over the course of 10 seconds, interpolating from a width of 40 to a width of 100 and back to 40.

<rect ...>
   <animate attributeName="width" values="40;100;40" dur="10s"/>
</rect>

The following "from-to animation" example animates the width of an SVG shape over the course of 10 seconds from a width of 50 to a width of 100.

<rect ...>
   <animate attributeName="width" from="50" to="100" dur="10s"/>
</rect>

The following "from-by animation" example animates the width of an SVG shape over the course of 10 seconds from a width of 50 to a width of 75.

<rect ...>
   <animate attributeName="width" from="50" by="25" dur="10s"/>
</rect>

The following "by animation" example animates the width of an SVG shape over the course of 10 seconds from the original width of 40 to a width of 70.

<rect width="40"...>
   <animate attributeName="width" by="30" dur="10s"/>
</rect>

The following "to animation" example animates the width of an SVG shape over the course of 10 seconds from the original width of 40 to a width of 100.

<rect width="40"...>
   <animate attributeName="width" to="100" dur="10s"/>
</rect>

3.2.3. Animation function calculation modes

By default, a simple linear interpolation is performed over the values, evenly spaced over the duration of the animation.  Additional attributes can be used for finer control over the interpolation and timing of the values. The calcMode attribute defines the basic method of applying values to the attribute. The keyTimes attribute provides additional control over the timing of the animation function, associating a time with each value in the values list. Finally, the keySplines attribute provides a means of controlling the pacing of interpolation between the values in the values list.

calcMode = "discrete | linear | paced | spline"
Specifies the interpolation mode for the animation. This can take any of the following values.  The default mode is "linear", however if the attribute does not support linear interpolation (e.g. for strings), the calcMode attribute is ignored and discrete interpolation is always used.
discrete
This specifies that the animation function will jump from one value to the next without any interpolation.
linear
Simple linear interpolation between values is used to calculate the animation function. 
This is the default calcMode.
paced
Defines interpolation to produce an even pace of change across the animation. This is only supported for values that define a linear numeric range, and for which some notion of "distance" between points can be calculated (e.g. position, width, height, etc.). If "paced" is specified, any keyTimes or keySplines will be ignored.
spline
Interpolates from one value in the values list to the next according to a time function defined by a cubic Bezier spline. The points of the spline are defined in the keyTimes attribute, and the control points for each interval are defined in the keySplines attribute.
keyTimes = "<list>"
A semicolon-separated list of time values used to control the pacing of the animation. Each time in the list corresponds to a value in the values attribute list, and defines when the value should be used in the animation function. Each time value in the keyTimes list is specified as a floating point value between 0 and 1 (inclusive), representing a proportional offset into the simple duration of the animation element.
If a list of keyTimes is specified, there must be exactly as many values in the keyTimes list as in the values list. 
Each successive time value must be greater than or equal to the preceding time value.
The keyTimes list semantics depends upon the interpolation mode: 

If there are any errors in the keyTimes specification (bad values, too many or too few values), the animation will have no effect.
If the simple duration is indefinite, any keyTimes specification will be ignored.

keySplines = "<list>"
A set of Bezier control points associated with the keyTimes list, defining a cubic Bezier function that controls interval pacing. The attribute value is a semi-colon separated list of control point descriptions. Each control point description is a set of four floating point values: x1 y1 x2 y2, describing the Bezier control points for one time segment. The keyTimes values that define the associated segment are the Bezier "anchor points", and the keySplines values are the control points.
Thus, there must be one fewer sets of control points than there are keyTimes
The values must all be in the range 0 to 1.
This attribute is ignored unless the calcMode is set to "spline".
If there are any errors in the keySplines specification (bad values, too many or too few values), the animation will have no effect.

If the keyTimes attribute is not specified, the values in the values attribute are assumed to be equally spaced through the animation duration, according to the calcMode:

Note that for the shorthand forms to animation and from-to animation, there are only 1 and 2 values respectively. Thus a discrete to animation will simply set the "to" value for the simple duration. A discrete from-to animation will set the "from" value for the first half of the simple duration and the "to" value for the second half of the simple duration.

Note that if the calcMode is set to "paced", the keyTimes attribute is ignored, and the values in the values attribute are spaced to produce a constant rate of change as the target attribute value is interpolated.

If the  argument values for keyTimes or keySplines are not legal (including too few or too many values for either attribute), the animation will have no effect (see also Handling syntax errors).

In the calcMode, keyTimes and keySplines attribute values, leading and trailing white space and white space before and after semi-colon separators will be ignored.

Examples

This example describes a somewhat unusual usage: "from-to animation" with discrete animation. The "stroke-linecap" attribute of SVG elements takes a string, and so implies a calcMode of discrete. The animation will set the stroke-linecap property to "round" for 5 seconds (half the simple duration) and then set the stroke-linecap to "square" for 5 seconds.

<rect stroke-linecap="butt"...>
   <animate attributeName="stroke-linecap" 
      from="round" to="square" dur="10s"/>
</rect>

This example illustrates the use of keyTimes:

<animate attributeName="x" dur="10s" values="0; 50; 100" 
     keyTimes="0; .8; 1" calcMode="linear"/>

The keyTimes values causes the "x" attribute to have a value of "0" at the start of the animation, "50" after 8 seconds (at 80% into the simple duration) and "100" at the end of the animation. The value will change more slowly in the first half of the animation, and more quickly in the second half.

Extending this example to use keySplines:

<animate attributeName="x" dur="10s" values="0; 50; 100" 
     keyTimes="0; .8; 1" calcMode="spline" 
     keySplines=".5 0 .5 1; 0 0 1 1" />

The keyTimes still causes the "x" attribute to have a value of "0" at the start of the animation, "50" after 8 seconds and "100" at the end of the animation. However, the keySplines values define a curve for pacing the interpolation between values. In the example above, the spline causes an ease-in and ease-out effect between time 0 and 8 seconds (i.e. between keyTimes 0 and .8, and values "0" and "50"), but a strict linear interpolation between 8 seconds and the end (i.e. between keyTimes .8 and 1, and values  "50" and "100"). See Figure 1 below for an illustration of the curves that these keySplines values define.

For some attributes, the pace of change may not be easily discernable by viewers. However for animations like motion, the ability to make the speed of the motion change gradually, and not in abrupt steps, can be important. The keySplines attribute provides this control.

The following figure illustrates the interpretation of the keySplines attribute. Each diagram illustrates the effect of keySplines settings for a single interval (i.e. between the associated pairs of values in the keyTimes and values lists.). The horizontal axis can be thought of as the input value for the unit progress of interpolation within the interval - i.e. the pace with which interpolation proceeds along the given interval. The vertical axis is the resulting value for the unit progress, yielded by the keySplines function. Another way of describing this is that the horizontal axis is the input unit time for the interval, and the vertical axis is the output unit time. See also the section Timing and real-world clock times.
Example keySplines01 - keySplines of 0 0 1 1 (the default) keySplines="0 0 1 1" (the default) Example keySplines02 - keySplines of .5 0 .5 1 keySplines=".5 0 .5 1"
 
Example keySplines03 - keySplines of .5 0 .5 1 keySplines="0 .75 .25 1" Example keySplines04 - keySplines of .5 0 .5 1 keySplines="1 0 .25 .25"

Figure 1: Illustration of keySplines effect

To illustrate the calculations, consider the simple example:

<animate dur="4s" values="10; 20" keyTimes="0; 1"
     calcMode="spline" keySplines={as in table} />

Using the keySplines values for each of the four cases above, the approximate interpolated values as the animation proceeds are:
keySplines values  Initial value After 1s After 2s After 3s Final value
0 0 1 1 10.0 12.5 15.0 17.5 20.0
.5 0 .5 1 10.0 11.0 15.0 19.0 20.0
0 .75 .25 1 10.0 18.0 19.3 19.8 20.0
1 0 .25 .25 10.0 10.1 10.6 16.9 20.0

For a formal definition of Bezier spline calculation, see:

Computer Graphics : Principles and Practice, Second Edition by James D. Foley, Andries van Dam, Steven K. Feiner, John F. Hughes, Richard L. Phillips, Addison-Wesley, pp. 488-491.

3.3. Specifying the animation effect F(t)

As described above, the animation function f(t) defines the animation for the simple duration. However SMIL Animation allows the author to repeat this, and to specify whether the animation should simply end when the active duration completes, or whether it should be frozen at the last value.  In addition, the author can specify how each animation should be combined with other animations and the original DOM value.

This section describes the syntax and associated semantics for the additional functionality. A detailed model for combining animations is described, along with a state model for animations, and additional details of the timing model.

The period of time during which the animation is actively playing, including any repeat behavior, is described as the active duration AD. The active duration may be computed from the simple duration and the repeat specification, and it may be constrained with the end attribute.  The complete rules for computing the active duration are presented in the section Computing the active duration.

3.3.1. Repeating animations

Repeating an animation causes the animation function f(t) to be "played" several times in sequence.  The author can specify either how many times to repeat, using repeatCount, or how long to repeat, using repeatDur. Each repeat iteration is one instance of "playing" the animation function f(t).

If the simple duration d is indefinite, the animation cannot repeat. See also the section Computing the active duration.

repeatCount
Specifies the number of iterations of the animation function. It can have the following attribute values:
numeric value
This is a (base 10) "floating point" numeric value that specifies the number of iterations. It can include partial iterations expressed as fraction values. A fractional value describes a portion of the simple duration d. Values must be greater than 0.
"indefinite"
The animation is defined to repeat indefinitely (i.e. until the document ends).
repeatDur
Specifies the total duration for repeat. It can have the following attribute values:
clock-value
Specifies the duration in presentation time to repeat the animation function f(t).
 
"indefinite"
The animation is defined to repeat indefinitely  (i.e. until the document ends).

At most one of repeatCount or repeatDur should be specified. If both are specified (and the simple duration is not indefinite), the active duration is defined as the minimum of the specified repeatDur, and the simple duration multiplied by repeatCount. For the purposes of this comparison, a defined value is considered to be "less than" a value of "indefinite". If the simple duration is indefinite, and both repeatCount and repeatDur are specified, the repeatCount will be ignored, and the repeatDur will be used (refer to the examples below describing repeatDur and an indefinite simple duration). These rules are included in the section Computing the active duration.

Examples

In the following example, the 2.5 second animation function will be repeated twice; the active duration AD will be 5 seconds.

<animate attributeName="top" from="0" to="10" dur="2.5s"
         repeatCount="2"
/>

In the following example, the animation function will be repeated two full times and then the first half is repeated once more; the active duration AD will be 7.5 seconds.

<animate attributeName="top" from="0" to="10" dur="3s"
         repeatCount="2.5"
/>

In the following example, the animation function will repeat for a total of 7 seconds. It will play fully two times, followed by a fractional part of 2 seconds. This is equivalent to a repeatCount of 2.8. The last (partial) iteration will apply values in the range "0" to "8". 

<animate attributeName="top" from="0" to="10" dur="2.5s"
         repeatDur="7s" />

Note that if the simple duration is not defined (e.g. it is indefinite), repeat behavior is not defined (but repeatDur still defines the active duration). In the following example the simple duration is indefinite, and so the repeatCount is effectively ignored. Nevertheless, this is not considered an error. The active duration AD is also indefinite. The effect of the animation is to set the fill color to red (i.e. to just use the value for f(0)) for the remainder of the document duration.

<animate attributeName="fill" from="red" to="blue" repeatCount="2" />

In the following example, the simple duration is indefinite, and so repeat behavior is not meaningful. However, the repeatDur still determines the active duration AD. The effect of the animation is to set the fill color to red for 10 seconds.

<animate attributeName="fill" from="red" to="blue" repeatDur="10s" />

In the following example, the simple duration is longer than the duration specified by repeatDur, and so the active duration will effectively cut short the simple duration. However, animation function still uses the specified simple duration. The effect of the animation is to interpolate the value of "top" from 10 to 15, over the course of 5 seconds.

<animate attributeName="top" from="10" to="20" 
         dur="10s" repeatDur="5s"
/>

Controlling behavior of repeating animation - Cumulative animation

The author may also select whether a repeating animation should repeat the original behavior for each iteration, or whether it should build upon the previous results, accumulating with each iteration. For example, a motion path that describes an arc can repeat by moving along the same arc over and over again, or it can begin each repeat iteration where the last left off, making the animated element bounce across the window. This is called cumulative animation.

Using the path notation for a simple arc, we describe this example as:

<img ...>
   <animateMotion path="c( 3 5 8 5 10 0)" dur="10s"
      accumulate="sum" repeatCount="10" />
</img>

@@ Pictures would help here

The image moves from the original position along the arc over the course of 10 seconds. As the animation repeats, it builds upon the previous value and begins the second arc where the first one ended. In this way, the image "bounces" across the screen. This could be described as a complete path, but the path description would get quite large, and would be more cumbersome to edit.

Note that cumulative animation only controls how a single animation accumulates the results of the animation function as it repeats. It specifically does not control how one animation interacts with other animations to produce a presentation value. This latter behavior is described in the section Additive animation.

Any numeric attribute that supports addition can support cumulative animation. For example, we can grow the "width" of an SVG "rect" element by 100 pixels in 100 seconds.

<rect width="20px"...>
   <animate attributeName="width" by="10px" dur="10s"
      accumulate="sum" repeatCount="10" />
</rect>

After 10 seconds, the rectangle is 30 pixels wide. The animation repeats, and builds upon the previous values growing to 40 pixels after 20 pixels, and up to 120 pixels wide after all ten repeats.

The behavior of repeating animations is controlled with the accumulate attribute:

accumulate = "none | sum"
Controls whether or not the animation is cumulative. 
If "sum", each repeat iteration after the first builds upon the last value of the previous iteration.
If "none", repeat iterations are not cumulative, and simply repeat the animation function f(t). This is the default.
This attribute is ignored if the target attribute value does not support addition, or if the animation element does not repeat.
Cumulative animation is not defined for "to animation". This attribute will be ignored if the animation function is specified with only the to attribute. See also Specifying function values.

To produce the cumulative animation behavior, the animation function f(t) must be modified slightly. Each iteration after the first must add in the last value of the previous iteration - this is expressed as a multiple of the last value specified for the animation function. Note that cumulative animation is defined in terms of the values specified for the animation behavior, and not in terms of sampled or rendered animation values. The latter would vary from machine to machine, and could even vary between document views on the same machine.

Let fi(t) represent the cumulative animation function for a given iteration i.

The first iteration f0(t) is unaffected by accumulate, and so is the same as the original animation function definition.

f0(t) = f(t)

Let ve be the last value specified for the animation function (e.g. the "to" value or the last value in a "values" list).  Each iteration after the first (i.e. fi(t) where i >= 1 ) adds in the computed offset:

fi(t) = (ve * i) + f(t)

3.3.2. Controlling the active duration

SMIL Animation provides an additional control over the active duration. The end attribute allows the author to constrain the active duration of the animation by specifying an end value, using a simple offset, a time base, an event-base or DOM methods calls. The end attribute can constrain (but not extend) the active duration that is otherwise defined by dur and any repeat behavior. The rules for combining the attributes to compute the active duration are presented in the next section, Computing the active duration.

end
Defines an end value for the animation that can constrain the active duration.
The attribute value can be one of the following types of values:
clock-value
Specifies the presentation time of the end. The end value is thus defined relative to the document begin.
syncbase-value : ( id-ref ) ( ".begin" | ".end" )? ( "+"clock-value )?
Describes a syncbase and an offset from that syncbase. The end value is defined relative to the begin B or active end AE of another animation.
event-value : ( id-ref "." )? ( event-ref  ) ( "+"clock-value )?
Describes an event and an optional offset that determine the end value. The end value is defined relative to the time that the event is raised. The event must be raised after the animation begins, and before the active duration otherwise ends (e.g. as defined by repeatDur). Events may be any event defined for the host language in accordance with [DOM2Events]. These may include user-interface events, event-triggers transmitted via a network, etc. Details of event-based timing are described in the section below on Unifying event-based and scheduled timing.
"indefinite"
The end value of the animation will be determined by an "endElement()" method call. The SMIL Animation DOM methods are described in the Supported methods section.

If end specifies an event-value or syncbase-value that is not resolved, the end value is considered indefinite (until resolved).

In the following example, the active duration will end at the earlier of 10 seconds, or the end of the "foo" element. This is particularly useful if "foo" is defined to begin or end relative to an event.

<animate dur="2s" repeatDur="10s" end="foo.end" ... />

In the following example, the animation begins when the user clicks on the target element. The active duration will end 30 seconds after the document begins. Note that if the user has not clicked on the target element before 30 seconds elapse, the animation will never begin.

<animate begin="click" dur="2s" repeatDur="indefinite"
         end="30s" ... />

Using end with an event value enables authors to end an animation based on either an interactive event or a maximum active duration. This is sometimes known as lazy interaction.

In this example, a presentation describes factory processes. It uses animation to move an image around (e.g. against a background), demonstrating how an object moves from one part of a factory to another. Each step is a motion path, and set to repeat 3 times to make the point clear. Each animation can also be ended by clicking on some element "next" that allows the user to advance the presentation to the next step.

<img id="objectToMove" ... >
  <animateMotion id="step1" begin="0" dur="5s"
     repeatCount="3" end="next.click" path.../>
  <animateMotion id="step2" begin="step1.end" dur="5s"
     repeatCount="3" end="next.click" path.../>
  <animateMotion id="step3" begin="step2.end" dur="5s"
     repeatCount="3" end="next.click" path.../>
  <animateMotion id="step4" begin="step3.end" dur="5s"
     repeatCount="3" end="next.click" path.../>
  <animateMotion id="step5" begin="step4.end" dur="5s"
     repeatCount="3" end="next.click" path.../>
</img>

In this case, the active end of each animation is defined to be the earlier of 15 seconds after it begins, or a click on "next". This lets the viewer sit back and watch, or advance the presentation at a faster pace.

3.3.3. Computing the active duration

The table in Figure 2 shows the semantics of all possible combinations of simple duration, repeatCount and repeatDur, and end. The following conventions are used in the table:

Additionally, the following rules must be followed in computing values:

Some of the rules and results that are implicit in the table, and that should be noted in particular are:

Simple
duration d
repeatCount repeatDur end Active Duration
defined       d
defined defined     repeatCount*d
defined   defined   repeatDur
defined     defined MIN( d, end-B )
defined defined defined   MIN( repeatCount*d, repeatDur )
defined defined   defined MIN( repeatCount*d, ( end-B ))
defined   defined defined MIN( repeatDur, ( end-B ))
defined defined defined defined MIN( repeatCount*d, repeatDur, ( end-B ))
indefinite *     indefinite
indefinite * defined   repeatDur
indefinite *   defined end-B
indefinite * defined defined MIN( repeatDur, ( end-B ))
* indefinite     indefinite
*   indefinite   indefinite
* indefinite indefinite   indefinite
* indefinite   defined end-B
*   indefinite defined end-B
* indefinite indefinite defined end-B
Figure 2: Computing the active duration for different combinations of simple duration, repeatCount and repeatDur, and end.

3.3.4. Freezing animations

By default when an animation element ends, its effect is no longer applied to the presentation value for the target attribute. For example, if an animation moves an image and the animation element ends, the image will "jump back" to its original position.

<img top="3" ...>
   <animate begin="5s" dur="10s" attributeName="top" by="100"/>
</img>

The image will appear stationary at the top value of "3" for 5 seconds, then move 100 pixels down in 10 seconds. 15 seconds after the document begin, the animation ends, the effect is no longer applied, and the image jumps back from 103 to 3 where it started (i.e. to the underlying value of the top attribute).

The fill attribute can be used to maintain the value of the animation after the active duration of the animation element ends:

<img top="3" ...>
   <animate begin= "5s" dur="10s" attributeName="top" by="100"
          fill="freeze" />
</img>

The animation ends 15 seconds after the document begin, but the image remains at the top value of 103. The attribute "freezes" the last value of the animation for the remainder of the document duration.

The freeze behavior of an animation is controlled using the "fill "attribute:

fill = "freeze | remove"
This attribute can have the following values:
freeze
The animation effect F(t) is defined to freeze the effect value at the last value of the active duration. The animation effect is "frozen" for the remainder of the document duration (or until the animation is restarted - see Restarting animations). 
remove
The animation effect is removed (no longer applied) when the active duration of the animation is over. After the active end AE of the animation, the animation no longer affects the target (unless the animation is restarted - see Restarting animations).
This is the default value.

This functionality is also useful when a series of motions are defined that should build upon one another, as in this example:

<img ...>
   <animateMotion begin="0" dur="5s" path="[some path]"
           additive="sum" fill="freeze" />
   <animateMotion begin="5s" dur="5s" path="[some path]"
           additive="sum" fill="freeze" />
   <animateMotion begin="10s" dur="5s" path="[some path]"
           additive="sum" fill="freeze" />
</img>

The image moves along the first path, and then starts the second path from the end of the first, then follows the third path from the end of the second, and stays at the final point. The semantics of the additive attribute are defined in the next section.

Note that if the active duration cuts short the simple duration (including the case of partial repeats), then the freeze value is defined by the shortened simple duration. In the following example, the animation function repeats two full times and then again for one-half of the simple duration. In this case, the freeze value will be 15: 

<animate from="10" to="20" dur="4s" 
         repeatCount="2.5" fill="freeze" .../> 

In the following example, the dur attribute is missing, and so the simple duration is indefinite. The active duration is constrained by end to be 10 seconds. Since interpolation is not defined, the freeze value will be 10:

<animate from="10" to="20" end="10s" fill="freeze" .../> 
Comparison to SMIL timing

SMIL Animation specifies that fill="freeze" remains in effect for the remainder of the document, or until the element is restarted. In the more general SMIL timing model that allows time containers, the duration of the freeze effect is controlled by the time container, and never extends past the end of the time container simple duration. While this may appear to conflict, the SMIL Animation definition of fill="freeze" is consistent with the SMIL timing model. It is simply the case that in SMIL Animation, the document is the only "time container", and so the effect is as described above.

3.3.5. Additive animation

It is frequently useful to define animation as an offset or delta to an attribute's value, rather than as absolute values. A simple "grow" animation can increase the width of an object by 10 pixels:

<rect width="20px" ...>
   <animate attributeName="width" from="0px" to="10px" dur="10s"
      additive="sum"/>
</rect>

The width begins at 20 pixels, and increases to 30 pixels over the course of 10 seconds.  If the animation were declared to be non-additive, the same from and to values would make the width go from 0 to 10 pixels over 10 seconds.

In addition, many complex animations are best expressed as combinations of simpler animations. A "vibrating" path, for example, can be described as a repeating up and down motion added to any other motion:

<img ...>
   <animateMotion from="0,0" to="100,0" dur="10s" />
   <animateMotion values="0,0; 0,5; 0,0" dur="1s"
                  repeatDur="10s" additive="sum"/>
</img>

When there are multiple animations defined for a given attribute that overlap at any moment, the two either add together or one overrides the other. Animations overlap when they are both either active or frozen at the same moment. The ordering of animations (e.g. which animation overrides which) is determined by a priority associated with each animation. The animations are prioritized according to when each begins. The animation first begun has lowest priority and the most recently begun animation has highest priority.

Higher priority animations that are not additive will override all earlier animations, and simply set the attribute value.  Animations that are additive apply (i.e. add to) to the result of the earlier-activated animations. For details on how animations are combined, see The animation sandwich model.

The additive behavior of an animation is controlled by the additive attribute:

additive = "replace | sum"
Controls whether or not the animation is additive. 
sum
Specifies that the animation will add to the underlying value of the attribute and other lower priority animations.
replace
Specifies that the animation will override the underlying value of the attribute and other lower priority animations. This is the default, however the behavior is also affected by the animation value attributes by and to, as described below.

Additive animation is defined for numeric attributes and other data types for which some addition function is defined. This includes numeric attributes for concepts such as position, widths and heights, sizes, etc. This also includes color (refer to The animateColor element), and may include other data types as specified by the host language.

While many animations of numerical attributes will be additive, this is not always the case. As an example of an animation that is defined to be non-additive, consider a hypothetical extension animation "mouseFollow" that causes an object to track the mouse. 

<img ...>
   <animateMotion dur=10s repeatDur="indefinite"
           path="[some nice path]" />
   <mouseFollow begin="mouseover" dur="5s"
           additive="replace" fill="remove" />
</img>

The mouse-tracking animation runs for 5 seconds every time the user mouses over the image. It cannot be additive, or it will just offset the motion path in some odd way. The mouseFollow needs to override the animateMotion while it is active. When the mouseFollow completes, its effect is no longer applied and the animateMotion again controls the presentation value for position.

In addition, some numeric attributes (e.g. a telephone number attribute) may not sensibly support addition - it is left to the host language to specify which attributes support additive animation. Attribute types such as strings and Booleans, for which addition is not defined, cannot support additive animation.

How from, to and by attributes affect additive behavior.

The attribute values to and by, used to describe the animation function, can override the additive attribute in certain cases:

For the hybrid case of a "to-animation", the animation function f(t) is defined in terms of the underlying value, the specified to value, and the current value of t (i.e. time) relative to the simple duration d.

vcur  is the current base value (at time t)
vto   is the defined "to" value

f(t) = vcur + ((vto - vcur) * (t/d))

Note that if no other (lower priority) animations are active or frozen, this defines simple interpolation. However if another animation is manipulating the base value, the "to-animation" will add to the effect of the lower priority, but will dominate it as it nears the end of the simple duration, eventually overriding it completely. The value for F(t) when a "to-animation" is frozen (at the end of the simple duration) is just the to value. If a "to-animation" is frozen anywhere within the simple duration (e.g. using a repeatCount of "2.5"), the value for F(t) when the animation is frozen is the value computed for the end of the active duration. Even if other, lower priority animations are active while a "to-animation" is frozen, the value for F(t) does not change.

For an example of additive "to-animation", consider the following two additive animations. The first, a "by-animation" applies a delta to attribute "x" from 0 to -10. The second, a "to-animation" animates to a final value of 10.

 <foo x="0" .../>
    <animate id="A1" attributeName="x" 
        by="-10" dur="10s" fill="freeze" />
    <animate id="A2" attributeName="x" 
        to="10"  dur="10s" fill="freeze" />
 </foo>

The presentation value for "x" in the example above, over the course of the 10 seconds is presented in Figure 3 below. These values are simply computed using the formula described above. Note that the value for F(t) for A2 is the presentation value for "x".
Time F(t) for A1 F(t) for A2
 0 0 0
 1 -1 0.1
 2 -2 0.4
 3 -3 0.9
 4 -4 1.6
 5 -5 2.5
 6 -6 3.6
 7 -7 4.9
 8 -8 6.4
 9 -9 8.1
10 -10 10

Figure 3:  Effect of Additive to-animation example

 

Additive and Cumulative animation

The "accumulate" attribute should not be confused with the  "additive" attribute. The "additive" attribute defines how an animation is combined with other animations and the base value of the attribute.  The "accumulate" attribute defines only how the animation function interacts with itself, across repeat iterations.

Typically, authors expect cumulative animations to be additive (as in the examples described for accumulate above), but this is not required. The following example is not additive.

<img ...>
   <animate dur="10s" repeatDur="indefinite"
            attributeName="top" from="20" by="10"
            additive="replace" accumulate="sum" />
</img>

The animation overrides whatever original value was set for "top", and begins at the value 20. It moves down by 10 pixels to 30, then repeats. It is cumulative, so the second iteration starts at 30 and moves down by another 10 to 40. Etc.

When a cumulative animation is also defined to be additive, both features function normally. The accumulated effect for F(t) is used as the value for the animation, and is added to the underlying value for the target attribute. Refer also to The animation sandwich model.

3.3.6. Restarting animations

When an animation is defined to begin at a simple offset (e.g. begin="5s" ), there is an unequivocal time when the element begins. However, if an animation is defined to begin relative to an event (e.g. begin="foo.click" ), the event can happen at any time, and moreover can happen more than once (e.g. if the user clicks on "foo" several times). In some cases, it is desirable to restart an animation if a second begin event is received. In other cases, an author may want to preclude this behavior. The restart attribute controls the circumstances under which an animation is restarted:

restart = "always | whenNotActive | never"
always
The animation can be restarted at any time. 
This is the default value.
whenNotActive
The animation can only be restarted when it is not active (i.e. it can be restarted after the active end). Attempts to restart the animation during its active duration are ignored.
never
The animation cannot be restarted for the remainder of the document duration.

Note that there are several ways that an animation may be restarted. The behavior (i.e. to restart or not) in all cases is controlled by the restart attribute. The different restart cases are:

When an animation restarts, the defining semantic is that it behaves as though this were the first time the animation had begun, independent of any earlier behavior. The animation effect F(t) is defined independent of the restart behavior. Any effect of an animation playing earlier is no longer applied, and only the current animation effect F(t) is applied.

If an additive animation is restarted while it is active or frozen, the previous effect of the animation (i.e. before the restart) is no longer applied to the attribute. Note in particular that cumulative animation is defined only within the active duration of an animation. When an animation restarts, all accumulated context is discarded, and the animation effect F(t) begins accumulating again from the first iteration of the restarted active duration.

The restart setting for an animation is evaluated when the syncbase element restarts, when the eventbase event happens, or when the DOM method call (e.g. beginElement()) happens. For example:

<img ...>
   <animate id="foo" begin="click" ..." />
   <animate id="bar" begin="foo.begin+2s" dur="10s" 
       restart="whenNotActive" ..." />
</img>

If the user clicks on the image at 5 seconds, animation "foo" will begin, and animation "bar" will be scheduled to begin at 7 seconds. If the user clicks the image again at 6 seconds, "foo" would restart, and "bar" would be rescheduled to start at 8 seconds.  If the user clicks again at 9 seconds, "foo" would restart but "bar" will not, as it is set to allow restart only when it is not active.

If an element is currently active when a restart is scheduled, the element should end immediately (at the time of the restart evaluation).  It should not continue playing until the rescheduled begin actually happens. For example:

<img ...>
   <animate id="foo" begin="click" ..."/>
   <animate id="bar" begin="foo.begin+2s" dur="10s" />
</img>

If the user clicks the image once at 3 seconds, "foo" begins to play and 2 seconds later "bar" will play as well. If the clicks again at 6 seconds, "foo" restarts immediately, "bar" is stopped, and "bar" will restart at 8 seconds.

Note that using restart can also allow the author to define a single UI event to both begin and end an element, as follows:

<img ...>
   <animate id="foo" begin="click" dur="2s"
       repeatDur="indefinite" end="click"
       restart="whenNotActive" ... />
</img>

If "foo" were defined with the default restart behavior "always", a second click on the image would simply restart the animation. However, since the second click cannot restart the animation when restart is set to "whenNotActive", the click will just end the active duration and stop the animation. This is sometimes described as "toggle" activation. See also Unifying event-based and scheduled timing.

Comparison to SMIL timing

SMIL Animation specifies that restart="never" precludes restart for the remainder of the document duration. In the more general SMIL Boston timing model that allows time containers, the duration of the restart="never" semantic is defined by the time container, and only extends to the end of the time container simple duration. While this may appear to conflict, the SMIL Animation definition of restart="never" is consistent with the SMIL timing model. It is simply the case that in SMIL Animation, the document is the only "time container", and so the effect is as described above.

3.4. Handling syntax errors

The specific error handling mechanisms for each attribute are described with the individual syntax descriptions.  However, some of these specifications describe the behavior of an animation with syntax errors as "having no effect".  This means that the animation will continue to behave normally with respect to timing, but will not manipulate any presentation value, and so will have no visible impact upon the presentation. 

In particular, this means that if other animation elements are defined to begin or end relative to an animation that "has no effect", the other animation elements will begin and end as though there were no syntax errors. The presentation runtime may indicate an error, but need not halt presentation or animation of the document. Some host languages and/or runtimes may choose to impose stricter error handling (see also Error handling semantics for a discussion of host language issues with error handling). Authoring environments may also choose to be more intrusive when errors are detected.

3.5. The animation sandwich model

When an animation is running, it does not actually change the attribute values in the DOM.  The animation runtime must maintain a presentation value for any target attribute, separate from the DOM, CSS, or other object model (OM) in which the target attribute is defined. The presentation value is reflected in the display form of the document. The effect of animations is to manipulate this presentation value, and not to affect the underlying DOM or CSS OM values.

The remainder of this discussion uses the generic term OM for both the XML DOM [DOM-Level-2] as well as the CSS-OM. If an implementation does not support an object model, it must maintain the original value as defined by the document as well as the presentation value; for the purposes of this section, we will consider this original value to be equivalent to the value in the OM.

The model accounting for the OM and concurrently active or frozen animations for a given attribute is described as a "sandwich", an analogy to the layers of meat and cheeses in a "submarine sandwich". On the bottom of the sandwich is the base value taken from the OM. Each active (or frozen) animation is a layer above this. The layers (i.e. the animations) are placed on the sandwich in order according to priority, with higher priority animations placed above lower priority animations. Note that animations manipulate the presentation value coming out of the OM in which the attribute is defined, and pass the resulting value on to the next layer of document processing. This does not replace or override any of the normal document OM processing cascade. 

Specifically, animating an attribute defined in XML will modify the presentation value before it is passed through the style sheet cascade, using the XML DOM value as its base. Animating an attribute defined in a style sheet language will modify the presentation value passed through the remainder of the cascade. 

In both the DOM 2 CSS-OM and in CSS2, the terms "specified", "computed" and "actual" are used to describe the results of evaluating the syntax, the cascade and the presentation rendering. When animation is applied to CSS properties of a particular element, the base value to be animated is read using the (readonly) getComputedStyle() method on that element. The values produced by the animation are written into an override stylesheet for that element, which may be obtained using it's getOverrideStyle() method. These new values then affect the cascade and are reflected in a new computed value (and thus, modified presentation). This means that the effect of animation overrides all style sheet rules, except for user rules with the !important property. This enables !important user style settings to have priority over animations, an important requirement for accessibility. Note that the animation may have side-effects upon the document layout. See also the [CSS2] specification (the terms are defined in section 6.1).

Within an OM, animations are prioritized according to when each begins. The animation first begun has lowest priority and the most recently begun animation has highest priority. When two animations start at the same moment in time, the activation order is resolved as follows:

Note that if an animation is restarted (see also Restarting animations), it will always move to the top of the priority list, as it becomes the most recently activated animation. That is, when an animation restarts, its layer is pulled out of the sandwich, and added back on the very top.  Note also that when an element repeats, the priority is not affected (repeat behavior is not defined as restarting).

Each additive animation adds its effect to the result of all sandwich layers below. A non-additive animation simply overrides the result of all lower sandwich layers. The end result at the top of the sandwich is the presentation value that must be reflected in the document view.

Some attributes that support additive animation have a defined legal range for values (e.g. an opacity attribute may allow values between 0 and 1). In some cases, an animation function may yield out of range values. It is up to the implementation to clamp the results at the top of the animation stack to the legal range before applying them to the presentation value. However, the effect of all the animations in the stack should be combined, before any clamping is performed. Although individual animation functions may yield out of range values, the combination of additive animations in the animation stack may still be legal. Clamping only the final result and not the effect of the individual animation functions provides support for these cases. The host language must define the clamping semantics for each attribute that can be animated.  As an example, this is defined for The animateColor element

Initially, before any animations for a given attribute are active, the presentation value will be identical to the original value specified in the document (the OM value).

When all animations for a given attribute have completed and the associated animation effects are no longer applied, the presentation value will again be equal to the OM value. Note that if any animation is defined with fill="freeze", the effect of the animation will be applied as long as the document is displayed, and so the presentation value will reflect the animation effect until the document end. Refer also to the section "Freezing animations".

Some animations (e.g. animateMotion) will implicitly target an attribute, or possibly several attributes (e.g. the "posX" and "posY" attributes of some layout model). These animations must be placed in the respective animation stack for each attribute that is affected. Thus, e.g. an animateMotion animation may be in more than one animation stack (depending upon the layout model of the host language). For animation elements that implicitly target attributes, the host language designer must specify what attributes are implicitly targeted, and the runtime must maintain the animation stacks accordingly. 

Note that any queries (via DOM interfaces) on the target attribute will reflect the OM value, and will not reflect the effect of animations. Note also that the OM value may still be changed via the OM interfaces (e.g. using script). While it may be useful or desired to provide access to the final presentation value after all animation effects have been applied, such an interface is not provided as part of SMIL Animation. A future version may address this.

Although animation does not manipulate the OM values, the document display must reflect changes to the OM values. Host languages can support script languages that can manipulate attribute values directly in the OM. If an animation is active or frozen while a change to the OM value is made, the behavior is dependent upon whether the animation is defined to be additive or not, as follows: (see also the section Additive animation). 

3.6. State transition model

At any moment in time, an animation is in exactly one of the following states: idle, active, finished or frozen. The state transitions are caused by events called start, restart, freeze and stop. Figure 4 shows the legal transitions between the states of an animation:

State Diagram

Figure 4: State diagram of an animation

 

The following sections explain the semantics of the states and transitions of an animation, and explain how to define the transitions using attributes of the animation element.

Note that there is no transition allowed from the Frozen state to the Finished state. This is a result of the fact that SMIL Animation does not support time containers. Once an element is frozen, it remains frozen until the documents ends, or until a restart transition makes it active again.

Initial State: Idle

When the document that contains an animation element is first presented, the animation is created in the idle state. This is the common starting state for all animation elements. 

In the idle state an animation is inactive and does not affect the presentation of the document in any way. The animation simply waits for the time or event specified in its begin attribute. Note that the animation may transition immediately to the active state if the value of the begin attribute is zero (the default).

Start Transition: Idle to Active

An animation in the idle state transitions to the active state when the condition specified in the begin attribute becomes true. As described in the section on the begin attribute, this condition may depend upon one of several factors:

Additionally, an animation element may be started by a DOM beginElement() or  beginElementAt() method call, or as the result of being the target of an activated hyperlink.

Active State:

In the active state, an animation performs the transformation of its specified presentation values. The active state includes the entire active duration of the animation. The active duration of an animation element is specified by the interaction between the dur, end, repeatDur, and repeatCount attributes as detailed in the sections above describing those attributes, and in Computing the active duration.

Freeze Transition: Active to Frozen

If an animation has the fill attribute set to freeze, upon reaching the end of its active duration, the animation will transition to the frozen state. 

Frozen State:

In the frozen state the animation will continue to apply its final transformation of the specified presentation values for the remainder of the document presentation time, unless restarted.

Stop Transition: Active to Finished

If an animation has the fill attribute set to remove (the default), upon reaching the end of its active duration, the animation will transition to the finished state.

Finished State:

In the finished state the animation will no longer affect the presentation of the document, unless restarted.

Restart Transition: Frozen to Active

The ability of an animation element to make this transition depends upon the value of the restart attribute. If the restart attribute value is always or whenNotActive the animation element will transition to the active state in response to a DOM beginElement() or  beginElementAt() method call, or an additional begin event. The restart transition effectively resets the state of the animation element; the element's simple and active duration must be recomputed as if it were being started for the first time.

Restart Transition: Active to Active

An animation element may receive a DOM beginElement() or  beginElementAt() method call or may receive an additional begin event while in the active state. In this case, if the value of the restart attribute is always the animation element will re-transition to the active state and restart as described above. Any other value for the restart attribute will prevent this transition from occurring. 

Restart Transition: Finished to Active

An animation element restart can result from a DOM call or an additional begin event, subject to the restrictions imposed by the restart attribute. When in the finished state, an animation element may re-transition to the active state if the value of the restart attribute is always or whenNotActive. Any other value for the restart attribute will prevent this transition from occurring.

3.7. Timing model details

3.7.1. Timing and real-world clock times

Throughout this specification, animation is described as a function of "time". In particular, the animation function is described as producing a value for any "time" in the range of the simple duration. However, the simple duration can be repeated, and the animation can begin and restart in many ways.  As such, there is no direct relationship between the "time" that an animation function uses, and the real world concept of time as reflected on a clock.

When a keySplines attribute is used to adjust the pacing between values in an animation, the semantics can be thought of as changing the pace of time in the given interval. An equivalent model is that keySplines simply changes the pace at which interpolation progresses through the given interval. The two interpretations are equivalent mathematically, and the significant point is that the notion of "time" as defined for the animation function f(t) should not be construed as real world clock time. For the purposes of animation, "time" can behave quite differently from real world clock time.

3.7.2. Interval timing

SMIL Animation assumes the most common model for interval timing. This describes intervals of time (i.e. durations) in which the begin time of the interval is included in the interval, but the end time is excluded from the interval. This is also referred to as end-point exclusive timing. This model makes arithmetic for intervals work correctly, and provides sensible models for sequences of intervals.

Background rationale

In the real world, this is equivalent to the way that seconds add up to minutes, and minutes add up to hours.  Although a minute is described as 60 seconds, a digital clock never shows more than 59 seconds. Adding one more second to "00:59" does not yield "00:60" but rather "01:00", or 1 minute and 0 seconds. The theoretical end time of 60 seconds that describes a minute interval is excluded from the actual interval.

In the world of media and timelines, the same applies: Let A be a video, a clip of audio, or an animation. Assume "A" begins at 10 and runs until 15 (in any units - it does not matter). If "B" is defined to follow "A", then it begins at 15 (and not at 15 plus some minimum interval). When a runtime actually renders out frames (or samples for audio), and must render the time "15", it should not show both a frame of "A" and a frame of "B", but rather should only show the new element "B". This is the same for audio, or for any interval on a timeline. If the model does not use endpoint-exclusive timing, it will draw overlapping frames, or have overlapping samples of audio, of sequenced animations, etc.

Note that transitions from "A" to "B" also adhere to the interval timing model. They do require that "A" not actually end at 15, and that both elements actually overlap. Nevertheless, the "A" duration is simply extended by the transition duration (e.g. 1 second). This new duration for "A" is also endpoint exclusive - at the end of this new duration, the transition will be complete, and only "B" should be rendered - "A" is no longer needed.

Implications for animation

For animation, several results of this are important: the definition of repeat, and the value sampled during the "frozen" state.

When repeating an animation, the arithmetic follows the end-point exclusive model. Consider the example:

  <animation dur="4s" repeatCount="4" .../>

At time 0, the simple duration is sampled at 0, and the first value is applied.  This is the inclusive begin of the interval. The simple duration is sampled normally up to 4 seconds. However, the appropriate way to map time on the active duration to time on the simple duration is to use the remainder of division by the simple duration:

  simpleTime = REMAINDER( activeTime, d ) 

or

  F(t) = f( REMAINDER( t, d ) )  where t is within the active duration

Note: REMAINDER( t, d ) is defined as t - d*floor(t/d)

Using this, a time of 4 (or 8 or 12) maps to the time of 0 on the simple duration. The endpoint of the simple duration is excluded from (i.e. not actually sampled on) the simple duration.

This implies that the last value of an animation function f(t) may never actually be applied (e.g. for a linear interpolation).  In the case of an animation that does not repeat and does not specify fill="freeze", this may in fact be the case. However, in the following example, the appropriate value for the frozen state is clearly the "to" value:

  <animation from="0" to="5" dur="4s" fill=freeze .../>

This does not break the interval timing model, but does require an additional qualification for the animation function F(t) while in the frozen state:

The definition of accumulate also aligns to this model. The arithmetic is effectively inverted and values accumulate by adding in a multiple of the last value defined for the animation function f(t).

3.7.3. Unifying interactive and scheduled timing

SMIL Animation describes extensions to SMIL 1.0 to support interactive timing of animation elements. These extensions allow the author to specify that an animation should begin or end in response to an event (such as a user-input event like "click"), or to a hyperlink activation, or to a DOM method call.

The syntax to describe this uses event-value specifications and the special argument value "indefinite" for the begin and end attribute values. Event values describe user interface and other events. DOM method calls to begin or end an animation require that the associated attribute use the special value "indefinite". A hyperlink can also be targeted at an animation element that specifies begin="indefinite". The animation will begin when the hyperlink is activated (usually by the user clicking on the anchor). It is not possible to directly control the active end of an animation using hyperlinks.

Background

The current model represents an evolution from earlier multimedia runtimes. These were typically either pure, static schedulers or pure event-based systems.  Scheduler models present a linear timeline that integrates both discrete and continuous media.   Scheduler models tend to be good for storytelling, but have limited support for user-interaction. Event-based systems, on the other hand, model multimedia as a graph of event bindings.  Event-based systems provide flexible support for user-interaction, but generally have poor scheduling facilities; they are best applied to highly interactive and experiential multimedia.

The SMIL 1.0 model is primarily a scheduling model, but with some flexibility to support continuous media with unknown duration. User interaction is supported in the form of timed hyperlinking semantics, but there was no support for activating individual elements via interaction.

Modeling interactive, event-based content in SMIL

To integrate interactive content into SMIL timing, the SMIL 1.0 scheduler model is extended to support several new concepts: indeterminate timing, and activation of the element.

With indeterminate timing, an element has an undefined begin or active end time.  The element still exists within the constraints of the document, but the begin or active end time is determined by some external activation. Activation may be event-based (such as by a user-input event), hyperlink based (with a hyperlink targeted at the element), or DOM based (e.g. by a call to the beginElement() method).  From a scheduling perspective, the time is described as unresolved before the activation. Once the element begin or end has been activated, the time is resolved.

The event-activation support provides a means of associating an event with the begin or active end time for an element.  When the event is raised (e.g. when the user clicks on something), the associated time is resolved to a determinate time.  For event-based begin times, the element becomes active (begins to play) at the time that the event is raised (plus any specified offset). The element plays from the beginning of the animation function.  For event-based active end times, the element becomes inactive (stops playing) when the associated event is raised.

Note that an event based end will not be activated until the element has already begun. Any specified end event is ignored before the element begins.

Note that when an element restarts, any event-based end time that was resolved in the previous instance of play, will be reset to the unresolved state.

Related to event-activation is link-activation.  Hyperlinking has defined semantics in SMIL 1.0 to seek a document to a point in time. When combined with indeterminate timing, hyperlinking yields a variant on interactive content. A hyperlink can be targeted at an element that does not have a scheduled begin time. When the link is traversed, the element begins. The details of when hyperlinks activate an element, and when they seek the document timeline are presented in the next section. 

Note that hyperlink activation only applies to an element begin time, and not to the element end. Event and DOM based activation can apply to both begin and end times.

Note that elements can define the begin or end relative to another element, using a syncbase-value (the begin or end of another element). If the syncbase element is in turn defined with, for example, event-based times, the syncbase value is not resolved, and so the begin or end of the current element is also unresolved. For a begin or end time to be resolved, any referenced syncbase value must also be resolved.

3.7.4. Hyperlinks and timing

Hyperlinking semantics must be specifically defined for animation in order to ensure predictable behavior. Earlier hyperlinking semantics, such as those defined by SMIL 1.0 are insufficient because they do not handle indeterminate and interactive timing. Here we extend SMIL 1.0 semantics for use in presentations that include animations with indeterminate and interactive timing.

A hyperlink may be targeted at an animation element by specifying the value of the id attribute of an animation element in the fragment part of the link locator. Traversing a hyperlink that refers to an animation will behave according to the following rules:

  1. If the target animation is active, seek the document time back to the begin time of the element.
  2. Else if the target animation begin time is resolved, seek the document time (forward or back, as needed) to the resolved begin time of the target animation. Note that the begin time may be resolved as a result of an earlier hyperlink, DOM or event activation. Once the begin time is resolved, hyperlink traversal always seeks.
  3. Else (i.e. animation begin time is unresolved) just resolve the target animation begin time at current document time. Disregard the sync-base or event base of the animation, and do not "back-propagate" any timing logic to resolve the child, but rather treat it as though it were defined with begin="indefinite" and just resolve begin time to the current document time.

Note that hyperlink activation does not introduce any restart behavior, and is not subject to the restart attribute semantics.

If a seek of the document presentation time is required, it may be necessary to seek either forward or backward, depending upon the resolved begin time of the element and the current time at the moment of hyperlink traversal. 

After seeking a document forward, the document should be in the same state as if the user had allowed the presentation to run normally from the current time until reaching the animation element begin time (but had otherwise not interacted with the document). In particular, seeking the presentation time forward should also cause any other animation elements that have resolved begin times between the current time and the seeked-to time to begin. These elements may have ended, or may still be active or frozen at the seeked-to time, depending upon their begin times and active durations. Also any animation elements currently active at the time of hyperlinking should "fast-forward" over the seek interval. These may end or may be still active or frozen at the seeked- to time, depending upon their active durations. The net effect is that seeking forward to a presentation time puts the document into a state identical to that as if the document presentation time advanced undisturbed to reach the seek time.

If the resolved begin time for an animation element that is the target of a hyperlink is before the current presentation time, the presentation must seek backwards. Seeking backwards will rewind any animations active during the seek interval and will turn off any animations that are resolved to begin at a time after the seeked-to time. Note that resolved begin times (e.g. a begin associated with an event) are not cleared or lost by seeking to an earlier time. Subject to the rules above for hyperlinks that target animation elements, hyperlinking to elements with resolved begin times will function normally, advancing the presentation time forward to the previously resolved time.

These hyperlinking semantics assume that a record is kept of the resolved begin time for all animation elements, and this record is available to be used for determining the correct presentation time to seek to. Once resolved, begin times are not cleared. However, they can be overwritten by subsequent resolutions driven by multiple occurrences of an event (i.e. by restarting). For example: 

<animate id="A" begin="10s" .../>
<animate id="B" begin="A.begin+5s" .../>
<animate id="C" begin="click" .../>
<animate id="D" begin="C.begin+5s" .../>
...
<a href="#D">Click here!</a>

The begin time of elements "A" and "B" can be immediately resolved to be at 10 and 15 seconds respectively. The begin of elements "C" and "D" are unresolved when the document starts. Therefore activating the hyperlink will have no effect upon the presentation time or upon elements "C" and "D". Now, assume that "C" is clicked at 25 seconds into the presentation. The click on "C" in turn resolves "D" to begin at 30 seconds. From this point on, traversing the hyperlink will cause the presentation time to be seeked to 30 seconds.

If at 60 seconds into the presentation, the user again clicks on "C", "D" will become re-resolved to a presentation time of 65 seconds. Subsequent activation of the hyperlink will result in the seeking the presentation to 65 seconds.

3.7.5. Propagating changes to times

There are several cases in which times may change as the document is presented. In particular, when an animation time is defined relative to an event, the time (i.e. the animation begin or active end) is resolved when the event occurs. Another case arises with restart behavior - both the begin and active end time of an animation can change when it restarts. Since the begin and active end times of one animation can be defined relative to the begin or active end of other animations, any changes to times must be propagated throughout the document.

When an animation "foo" has a begin or active end time that specifies a syncbase element (e.g. "bar" as below):

<rect ...>
   <animate id="bar" end="click" .../>
   <animate id="foo" begin="bar.end" .../>
</rect>

we say that "foo" is a time-dependent of "bar" - that is, the "foo" begin time depends upon the active end of "bar". 

An element A is a time dependent of another element B if A specifies B as a syncbase element. In addition, if element A is a time dependent of element B, and if element B is a time dependent of element C (i.e. element B defines element C as a syncbase element), then element A is an indirect time dependent of element C.

When an element begins or ends, the time dependents of the element are effectively notified of the action, and the schedule for the time dependents may be affected. Note than an element must actually begin before any of the time dependents (dependent on the begin) are affected, and that an element must actually end before any of the time dependents (dependent on the end) are affected. This impacts the definition of the priority ordering of animation elements, as discussed in The animation sandwich model.

In the example above, any changes to the active end time of "bar" must be propagated to the begin of "foo". The effect of the changes depends upon the state of "foo" when the change happens, as detailed below.

If the begin time of an element is dependent upon another element (as for "foo" in the example), the resulting behavior when the syncbase element ("bar") propagates changes is determined as follows:

Note that the semantic is directly analogous to event-base timing and the restart attribute.

If the end time of an element is dependent upon another element, the semantic is much simpler:

Another way to think of this is that the end time is always recalculated, but it will not affect the presentation unless the element is currently active, or unless the element begins (or restarts) after the change happens.

3.8. Animation function value details

Animation function values must be legal values for the specified attribute. Three classes of values are described:

  1. Unitless scalar values. These are simple scalar values that can be parsed and set without semantic constraints. This class includes integers (base 10) and floating point (format specified by the host language).
  2. String values. These are simple strings.
  3. Language abstract values. These are values like CSS-length and CSS-angle values that have more complex parsing, but that can yield numbers that may be interpolated.

The animate element can interpolate unitless scalar values, and both animate and set elements can handle String values without any semantic knowledge of the target element or attribute. The animate and set elements must support unitless scalar values and string values. The host language must define which language abstract values should handled by these elements. Note that the animateColor element implicitly handles the abstract values for color values, and that the animateMotion element implicitly handles position and path values. 

In order to support interpolation on attributes that define numeric values with some sort of units or qualifiers (e.g. "10px", "2.3feet", "$2.99"), some additional support is required to parse and interpolate these values. One possibility is to require that the animation framework have built-in knowledge of the unit-qualified value types. However, this violates the principal of encapsulation and does not scale beyond CSS to XML languages that define new attribute value types of this form.

The recommended approach is for the animation implementation for a given host environment to support two interfaces that abstract the handling of the language abstract values. These interfaces are not formally specified, but are simply described as follows:

  1. The first interface converts a string (the animation function value) to a unitless, canonical number (either an integer or a floating point value). This allows animation elements to interpolate between values without requiring specific knowledge of data types like CSS-length. The interface will likely require a reference to the target attribute, to determine the legal abstract values. If the passed string cannot be converted to a unitless scalar, the animation element will treat the animation function values as strings, and the calcMode will default to "discrete".
  2. The second interface converts a unitless canonical number to a legal string value for the target attribute. This may, for example, simply convert the number to a string and append a suffix for the canonical units. The animation element uses the result of this to actually set the presentation value.

Support for these two interfaces ensures that an animation engine need not replicate the parser and any additional semantic logic associated with language abstract values. 

This is not an attempt to specify how an implementation provides this support, but rather a requirement for how values are interpreted. Animation behaviors should not have to understand and be able to convert among all the CSS-length units, for example. In addition, this mechanism allows for application of animation to new XML languages, if the implementation for a language can provide parsing and conversion support for attribute values.

3.9. Common syntax DTD definitions

Timing attributes

<!ENTITY % timingAttrs
  begin          CDATA  #IMPLIED 
  dur            CDATA  #IMPLIED
  end            CDATA  #IMPLIED
  restart        (always | never | 
                   whenNotActive)  "always"
  repeatCount    CDATA  #IMPLIED 
  repeatDur      CDATA  #IMPLIED
  fill           (remove | freeze) "remove"
>

Animation attributes

<!ENTITY % animAttrs
  attributeName  CDATA  #REQUIRED
  attributeType  CDATA  #IMPLIED
  additive       (replace | sum) "replace"
  accumulate     (none | sum) "none"
>
<!ENTITY % animTargetAttr
  targetElement  IDREF  #IMPLIED
>
<!ENTITY % animLinkAttrs
  type     (simple | extended | locator | arc) #FIXED "simple"
  show     (new | embed | replace) #FIXED 'embed'
  actuate  (user | auto) #FIXED 'auto'
  href     CDATA  #IMPLIED
>

4. Animation elements

4.1. The animate element

The <animate> element introduces a generic attribute animation that requires little or no semantic understanding of the attribute being animated.  It can animate numeric scalars as well as numeric vectors. It can also animate discrete sets of non-numeric attributes. The <animate> element is an empty element - it cannot have child elements.

This element supports from/to/by and values descriptions for the animation function, as well as all of the calculation modes. It supports all the described timing attributes. These are all described in respective sections above.

<!ELEMENT animate EMPTY>
<!ATTLIST animate
  %timingAttrs
  %animAttrs
  id             ID     #IMPLIED 
  calcMode       (discrete | linear | paced | spline ) "linear"
  values         CDATA  #IMPLIED
  keyTimes       CDATA  #IMPLIED
  keySplines     CDATA  #IMPLIED
  from           CDATA  #IMPLIED
  to             CDATA  #IMPLIED
  by             CDATA  #IMPLIED
>

Numerous examples are provided above.

4.2. The set element

The <set> element provides a simple means of just setting the value of an attribute for a specified duration. As with all animation elements, this only manipulates the presentation value, and when the animation completes, the effect is no longer applied. That is, <set> does not permanently set the value of the attribute. 

The <set> element supports all attribute types, including those that cannot reasonably by interpolated and that more sensibly support semantics of simply setting a value (e.g. strings and Boolean values). The set element is non-additive. The additive and accumulate attributes are not allowed.

The <set> element supports all the timing attributes to specify the simple and active durations. However, the repeatCount and repeatDur attributes will just affect the active duration of the <set>, extending the effect of the <set> (since it is not really meaningful to "repeat" a static operation). Note that using fill="freeze" with <set> will have the same effect as defining the timing so that the active duration is "indefinite".

The <set> element supports a more restricted set of attributes than the  <animate> element (in particular, only one value is specified, and no interpolation control is supported):

<!ELEMENT set EMPTY>
<!ATTLIST set
  %timingAttrs
  id             ID     #IMPLIED 
  attributeName  CDATA  #REQUIRED
  attributeType  CDATA  #IMPLIED
  to             CDATA  #IMPLIED
>
to = "<value>"
Specifies the value for the attribute during the duration of the <set> element. The argument value must match the attribute type. 

Examples

The following changes the stroke-width of an SVG rectangle from the original value to 5 pixels wide. The effect begins at 5 seconds and lasts for 10 seconds, after which the original value is again used.

<rect ...>
   <set attributeName="stroke-width" to="5px" 
            begin="5s" dur="10s" fill="remove" />
</rect>

The following example sets class attribute of the text element to the string "highlight" when the mouse moves over the element, and removes the effect when the mouse moves off the element. 

<text>This will highlight if you mouse over it...
   <set attributeName="class" to="highlight" 
            begin="mouseover" end="mouseout" />
</text>

4.3. The animateMotion element

In order to abstract the notion of motion paths across a variety of layout mechanisms, we introduce the <animateMotion> element. This describes motion in the abstract - the host language defines the layout model and must specify the precise semantics of motion.  

All values must be x, y value pairs. Each x and y value may specify any units supported for element positioning by the host language. The host language defines the default units. In addition, the host language defines the reference point for positioning an element. This is the point within the element that is aligned to the position described by the motion animation. The reference point defaults in some languages to the upper left corner of the element bounding box; in other languages (such as SVG) the reference point may be specified for the element.

The attributeName and attributeType attributes are not used with animateMotion, as the manipulated position attribute(s) are defined by the host language. If the position is exposed as an attribute or attributes that can also be animated (e.g. as "top" and "left", or "posX" and "posY"), implementations must combine <animateMotion> animations into the respective stacks with other animations that manipulate individual position attributes. See also the section The animation sandwich model.

The <animateMotion> element adds an additional syntax alternative for specifying the animation, the "path" attribute. This allows the description of a path using a subset of the SVG path syntax. Note that if a path is specified, it will override any specified values for values or from/to/by attributes. 

The default calculation mode (calcMode) for animateMotion is "paced". This will produce constant velocity motion along the specified path. Note that while animateMotion elements can be additive, authors should note that the addition of two or more "paced" (constant velocity) animations may not result in a combined motion animation with constant velocity.

<!ELEMENT animateMotion EMPTY>
<!ATTLIST animateMotion
  %timingAttrs
  id             ID     #IMPLIED 
  additive       (replace | sum) "replace"
  accumulate     (none | sum) "none"
  calcMode       (discrete | linear | paced | spline) "paced"
  values         CDATA  #IMPLIED
  from           CDATA  #IMPLIED
  to             CDATA  #IMPLIED
  by             CDATA  #IMPLIED
  keyTimes       CDATA  #IMPLIED
  keySplines     CDATA  #IMPLIED
  path           CDATA  #IMPLIED
  origin         (default) "default"
/>
path = "<path-description>"
Specifies the curve that describes the attribute value as a function of time. The supported syntax is a subset of the SVG path syntax. Support includes commands to describes lines ("MmLlHhVvZz") and Bezier curves ("Cc"). For details refer to the path specification in SVG [SVG]. 
Note that SVG provides two forms of path commands - "absolute" and "relative". These terms may appear to be related to the definition of additive animation and the "origin" attribute, however they should not be confused. The terms "absolute" and "relative" apply only to the definition of the path itself, and not to the operation of the animation. The "relative" commands define a path point relative to the previously specified point. The terms "absolute" and "relative" are unrelated to the definitions of both "additive" animation or the specification of the "origin".
Move To commands - "M <x> <y>" or "m <dx> <dy>"
Start a new sub-path at the given (x,y) coordinate. If a moveto is followed by multiple pairs of coordinates, the subsequent pairs are treated as implicit lineto commands.
Line To commands - "L <x> <y>" or "l <dx> <dy>"
Draw a line from the current point to the given (x,y) coordinate which becomes the new current point. A number of coordinate pairs may be specified to draw a polyline.
Horizontal Line To commands - "H <x>" or "h <dx>"
Draws a horizontal line from the current point (cpx, cpy) to (x, cpy). Multiple x values can be provided (although this generally only makes sense for the relative form).
Vertical Line To commands - "V <y>" or "v <dy>"
Draws a vertical line from the current point (cpx, cpy) to (cpx, y). Multiple y values can be provided (although generally only makes sense for the relative form).
Closepath commands - "Z" or "z"
The "closepath" causes an automatic straight line to be drawn from the current point to the initial point of the current subpath.
Cubic bezier Curve To commands - 
  "C <x1> <y1> <x2> <y2> <x> <y>" or 
  "c <dx1> <dy1> <dx2> <dy2> <dx> <dy>"
Draws a cubic Bezier curve from the current point to (x,y) using (x1,y1) as the control point at the beginning of the curve and (x2,y2) as the control point at the end of the curve. Multiple sets of coordinates may be specified to draw a polybezier.

When a path is combined with "linear" or "spline" calcMode settings, the number of values is defined to be the number of points defined by the path, unless there are "move to" commands within the path.  A "move to" command does not count as an additional point for the purpose of keyTimes and spline, and should not define an additional "segment" for the purposes of timing or interpolation. When a path is combined with a "paced" calcMode setting, all "move to" commands are considered to have 0 length (i.e. they always happen instantaneously), and should not be considered in computing the pacing.

calcMode 
Defined as above in Animation function calculation modes, but note that the default calcMode for animateMotion is "paced". This will produce constant velocity motion across the path.
The use of "discrete" for the calcMode together with a "path" specification is allowed, but is generally not useful (it will simply jump the target element from point to point).
The use of "linear" for the calcMode with more than 2 points described in "values", "path" or "keyTimes" may result in motion with varying velocity. The "linear" calcMode specifies that time is evenly divided among the segments defined by the "values" or "path" (note: any "keyTimes" list defines the same number of segments). The use of "linear" does not specify that time is divided evenly according to the distance described by each segment. 
For motion with constant velocity, calcMode should be set to "paced".
For complete velocity control, calcMode can be set to "spline" and the author can specify a velocity control spline with "keyTimes" and "keySplines".
origin = "default"
Specifies the origin of motion for the animation. The values and semantics of this attribute are dependent upon the layout and positioning model of the host language. In some languages, there may be only one option (i.e. "default"). However, in CSS positioning for example, it is possible to specify a motion path relative to the container block, or to the layout position of the element. It is often useful to describe motion relative to the position of the element as it is laid out (e.g. from off screen left to the layout position, specified as from="(-100, 0)" and to="(0, 0)". Authors must be able to describe motion both in this manner, as well as relative to the container block. The origin attribute supports this distinction. Nevertheless, because the host language defines the layout model, the host language must also specify the "default" behavior, as well as any additional attribute values that are supported.
Note that the definition of the layout model in the host language specifies whether containers have bounds, and the behavior when an element is moved outside the bounds of the layout container. In CSS2 [CSS2], for example, this can be controlled with the "clip" property.
Note that for additive animation, the "origin" distinction is not meaningful.  This attribute only applies when additive is set to "replace".

@@Should add an examples, although some are included above.

4.4. The animateColor element

The <animateColor> element specifies an animation of a color attribute. The host language must specify those attributes that describe color values, and that can support color animation. 

All values must represent sRGB color values. Legal value syntax for attribute values is defined by the host language. 

Interpolation is defined on a per-color-channel basis.

<!ELEMENT animateColor EMPTY>
<!ATTLIST animateColor
  %animAttrs
  %timingAttrs
  id             ID     #IMPLIED 
  calcMode       (discrete | linear
                  | paced | spline ) "linear"
  values         CDATA  #IMPLIED
  from           CDATA  #IMPLIED
  to             CDATA  #IMPLIED
  by             CDATA  #IMPLIED
  keyTimes       CDATA  #IMPLIED
  keySplines     CDATA  #IMPLIED
>

The values in the from/to/by and values attributes may specify negative and out of gamut values for colors.  The function defined by an individual animateColor may yield negative or out of gamut values.  The implementation must correct the resulting presentation value, to be legal for the destination (display) colorspace. However, as described in The animation stack model, the implementation should only correct the final result of all animations for a given attribute, and should not correct the effect of individual animations.

Values are corrected by "clamping" the values to the correct range. Values less than the minimum allowed value are clamped to the minimum value (commonly 0, but not necessarily so for some color profiles). Values greater than the defined maximum are clamped to the maximum value (defined by the attributeType domain) .

Note that color values are corrected by clamping them to the gamut of the destination (display) colorspace. Some implementations may be unable to process values which are outside the source (sRGB) colorspace and must thus perform clamping to the source colorspace, then convert to the destination colorspace and clamp to its gamut. The point is to distinguish between the source and destination gamuts; to clamp as late as possible, and to realize that some devices, such as inkjet printers which appear to be RGB devices, have non-cubical gamuts.

Note to implementers: When animateColor is specified as a "to animation", the animation function should assume Euclidean RGB-cube distance where deltas must be computed. See also Specifying function values and How from, to and by attributes affect additive behavior. Similarly, when the calcMode attribute for animateColor is set to "paced", the animation function should assume Euclidean RGB-cube distance to compute the distance and pacing.

5. Integrating SMIL Animation into a host language

This section describes what a language designer must actually do to specify the integration of SMIL Animation into a host language. This includes basic definitions, constraints upon animation, and allowed/supported events.

5.1. Required host language definitions

The host language designer must define some basic concepts in the context of the particular host language.  These provide the basis for timing and presentation semantics.

The host language designer must define what "presenting a document" means. A typical example is that the document is displayed on a screen.

The host language designer must define the document begin. Possible definitions are that the document begins when the complete document has been received by a client over a network, or that the document begins when certain document parts have been received.

The host language designer must define the document end. This is typically when the associated application exits or switches context to another document.

5.2. Required definitions and constraints on animation targets

Specifying the target element

The host language designer must choose whether to support the targetElement attribute, or the XLink attributes for specifying the target element. Note that if the XLink syntax is used, the host language designer must decide how to denote the XLink namespace for the associated attributes. The namespace can be fixed in a DTD, or the language designer can require colonized attribute names to denote the XLink namespace for the attributes. The required XLink attributes have fixed values, and so may also be specified in a DTD, or can be required on the animation elements. Host language designers may require that the optional XLink attributes be specified. These decisions are left to the host language designer - the syntax details for XLink attributes do not affect the semantics of SMIL Animation.

In general, target elements may be any element in the document. Host language designers must specify any exceptions to this. Host language designers are discouraged from allowing animation elements to target elements outside of the document in which the animation element is defined (the XLink syntax for the target element could allow this, but the SMIL timing and animation semantics of this are not defined in this version of SMIL Animation). 

Target attribute issues

The definitions in this module can be used to animate any attribute of any element in a host document. However, it is expected that host language designers integrating SMIL Animation may choose to constrain which elements and attributes can support animation. For example, a host language may not support animation of the language attribute of a script element. A host language which included a specification for DOM functionality might limit animation to the attributes which may legally be modified through the DOM.

Any attribute of any element not specifically excluded from animation by the host language may be animated, as long as the underlying data type (as defined by the host language for the attribute) supports discrete values (for discrete animation) and/or addition (for interpolated and additive animation).

All constraints upon animation must be described in the host language specification, as the DTD cannot reasonably express this.

The host language must define which language abstract values should handled for animated attributes. For example, a host language that incorporates CSS may require that CSS length values be supported. This is further detailed in Animation function value details.

The host language must specify the interpretation of relative values. For example, if a value is specified as a percentage of the size of a container, the host language must specify whether this value will be dynamically interpreted as the container size is animated.

The host language must specify the semantics of clamping values for attributes. The language must specify any defined ranges for values, and how out of range values will be handled.

The host language must specify the formats supported for numeric attribute values. This includes integer values and especially floating point values for attributes such as keyTimes and keySplines. As a reasonable minimum, host language designers are encouraged to support the format described in [CSS2]. The specific reference within the CSS specification for these data types is 4.3.1 Integers and real numbers.

Integrating animateMotion functionality

The host language specification must define which elements can be the target of animateMotion. In addition, the host language specification must describe the positioning model for elements, and must describe the model for animateMotion in this context (i.e. the semantics of the "default" value for the origin attribute must be defined). If there are different ways to describe position, additional attribute values for the origin attribute should be defined to allow authors control over the positioning model.

Example: SVG

As an example, SVG [SVG] integrates SMIL Animation. It specifies which of the elements, attributes and CSS properties may be animated.  Some attributes (e.g. "viewbox" and "fill-rule") support only discrete animation, and others (e.g. "width", "opacity" and "stroke") support interpolated and additive animation. An example of an attribute that does not support any animation is the "xlink:actuate" attribute on the <use> element (the value of this attribute is fixed to "auto" in the DTD).

@@ XLink syntax may be out of date (actuate=auto is now actuate=onLoad?). Once SVG/XLink settles on values for actuate, this section must be updated.

SVG details the format of numeric values, describing the legal ranges and allowing "scientific" (exponential) notation for floating point values.

5.3. Constraints on manipulating animation elements

Language designers integrating SMIL Animation are encouraged to disallow manipulation of attributes of the animation elements, after the document has begun. This includes both the attributes specifying targets and values, as well as the timing attributes. In particular, the id attribute (of type ID) on all animation elements must not be mutable (i.e. should be read-only). Requiring animation runtimes to track changes to id values introduces considerable complexity, for what is at best a questionable feature.

It is recommended that language specifications disallow manipulation of animation element attributes through DOM interfaces after the document has begun.  It is also recommended that language specifications disallow the use of animation elements to target other animation elements. 

Dynamically changing the attribute values of animation elements introduces semantic complications to the model that are not yet sufficiently resolved. This constraint may be lifted in a future version of SMIL Animation.

5.4. Required definitions and constraints on element timing

This specification assumes that animation elements are the only elements in the host language that have timing semantics (this restriction may be removed in a future version of SMIL Animation). This specification cannot be used for host languages that contain elements with timing semantics. For example, the following integration of animation with SMIL 1.0 is illegal with this version of SMIL animation:

<par id="illegalExample">
  <img begin="2s" dur="1m" src="foo.gif" />
    <anchor id="anc" href="#bar" coords="0%,0%,50%,50%" dur="30s" />
    <set targetElement="anc" attributeName="coords" 
         begin="10s" dur="20s" fill="freeze"
         to="50%,50%,100%,100%" />
  </img>
</par>

The set of "animation elements" that may have timing includes both the elements defined in this specification, as well as extension animation elements defined in host languages. Extension animation elements must conform to the animation framework described in this document.  In particular, extension animation elements may not be defined to contain other animation elements in a way that would introduce hierarchic timing as supported by the par and seq elements in SMIL 1.0 [SMIL].

Supported events for event-base timing

The host language must specify which event names are legal in event base values. If the host language defines no allowed event names, event-based timing is effectively precluded for the host language. 

Host languages may specify that dynamically created events (as per the [DOM2Events] specification) are legal as event names, and not explicitly list the allowed names.

5.5. Error handling semantics

The host language designer may impose stricter constraints upon the error handling semantics. That is, in the case of syntax errors, the host language may specify additional or stricter mechanisms to be used to indicate an error. An example would be to stop all processing of the document, or to halt all animation.

Host language designers may not relax the error handling specifications, or the error handling response (as described in Handling syntax errors). For example, host language designers may not define error recovery semantics for missing or erroneous values in the values or keyTimes attribute values.

5.6. SMIL Animation namespace

Language designers can choose to integrate SMIL Animation as an independent namespace, or can integrate SMIL Animation names into a new namespace defined as part of the host language. Language designers that wish to put the SMIL Animation functionality in an isolated namespace should use the following namespace:

@@ URI to be confirmed by W3C webmaster

http://www.w3.org/2000/TR/smil-animation10

6. Document Object Model support

Any XML-based language that integrates SMIL Animation will inherit the basic interfaces defined in DOM [DOM-Level-2] (although not all languages may require a DOM implementation). SMIL Animation specifies the interaction of animation and DOM. SMIL Animation also defines constraints upon the basic DOM interfaces, and specific DOM interfaces to support SMIL Animation.

Note that the language designer integrating SMIL Animation must specify any constraints upon SMIL Animation with respect to the DOM. This includes the specification of language attributes that can or cannot be animated, as well as the definition of addition for any attributes that support additive animation.

6.1. Event model

The SMIL Animation timing assumes that the host language supports events, and that the events can be bound in a declarative manner.  DOM Level 2 Events [DOM2Events] describes functionality to support this.

The specific events supported are defined by the host language. 

6.2. Supported interfaces

SMIL Animation supports several methods for controlling the behavior of animation: beginElement() and endElement(), et al. These methods are used to begin and end an animation that has declared the timing to respond to the DOM, using the following syntax:

<animate begin="indefinite" end="indefinite" .../>

Note that only one of begin or end need be specified - either or both can be used.  The beginElement() and beginElementAt() methods must do nothing if the animation is not explicitly set with the begin="indefinite" syntax above. The endElement() and endElementAt() methods must do nothing if the animation is not explicitly set with the end="indefinite" syntax above.

Calling beginElement() causes the animation to begin in the much same way that an animation with event-based begin timing begins. The effective begin time is the current presentation time at the time of the DOM method call. Note that beginElement() is subject to the restart attribute in the same manner that event-based begin timing is. If an animation is specified to disallow restarting at a given point, beginElement() methods calls must fail. Refer also to the section Restarting animations.

Calling beginElementAt() has the same effect as beginElement(), except that the effective begin time is offset from the current presentation time by an amount specified as a parameter. Passing a negative value for the offset causes the element to begin as for beginElement(), but has the effect that the element begins at the specified offset into its active duration. The beginElementAt() method must also respect the restart attribute. The restart semantics for a beginElementAt() method call are evaluated at the time of the method call, and not at the effective begin time specified by the offset parameter.

Calling endElement() causes an animation to end the active duration, just as end does. Depending upon the value of the fill attribute, the animation effect may no longer be applied, or it may be frozen at the current effect. Refer also to the section Freezing animations. If an animation is not currently active (i.e. if it has not yet begun or if it is frozen), the endElement() method will fail.

Calling endElementAt() causes an animation to end the active duration, just as endElement() does, but allows the caller to specify a positive offset, to cause the element to end at a point in the future. Other than delaying when the end actually happens, the semantics are identical to those for endElement(). If endElementAt() is called more than once while an element is active, the end time specified by the last method call will determine the end behavior. 

The expectation of the following interface is that an instance of the ElementTimeControl interface can be obtained by using binding-specific casting methods on an instance of an animate element. A DOM application can use the hasFeature method of the DOMImplementation interface to determine whether the ElementTimeControl interface is supported or not. The feature string for this interface is "TimeControl".

Interface ElementTimeControl

IDL Definition
interface ElementTimeControl {
  boolean            beginElement()
                                        raises(DOMException);
  boolean            beginElementAt(in float offset)
                                        raises(DOMException);
  boolean            endElement()
                                        raises(DOMException);
  boolean            endElementAt(in float offset)
                                        raises(DOMException);
};


Methods
beginElement
Causes this element to begin the local timeline (subject to restart constraints).
Return Value
boolean true if the method call was successful and the element was begun. false if the method call failed. Possible reasons for failure include:
  • The element doesn't support the beginElement method. (the begin attribute is not set to "indefinite")
  • The element is already active and can't be restarted when it is active. (the restart attribute is set to "whenNotActive")
  • The element is active or has been active and can't be restarted. (the restart attribute is set to "never").
Exceptions
DOMException SYNTAX_ERR: The element was not defined with the appropriate syntax to allow beginElement calls.
No Parameters

 

beginElementAt
Causes this element to begin the local timeline (subject to restart constraints), at the passed offset from the current time when the method is called. If the offset is >= 0, the semantics are equivalent to an event-base begin with the specified offset. If the offset is < 0, the semantics are equivalent to beginElement(), but the element active duration is evaluated as though the element had begun at the passed (negative) offset from the current time when the method is called.
Parameters
float offset The offset in seconds at which to begin the element.
Return Value
boolean true if the method call was successful and the element was begun. false if the method call failed. Possible reasons for failure include:
  • The element doesn't support the beginElementAt method. (the begin attribute is not set to "indefinite")
  • The element is already active and can't be restarted when it is active. (the restart attribute is set to "whenNotActive")
  • The element is active or has been active and can't be restarted. (the restart attribute is set to "never").
Exceptions
DOMException SYNTAX_ERR: The element was not defined with the appropriate syntax to allow beginElementAt calls.

 

endElement
Causes this element to end the local timeline.
Return Value
boolean true if the method call was successful and the element was ended. false if method call failed. Possible reasons for failure include:
  • The element doesn't support the endElement method. (the end attribute is not set to "indefinite")
  • The element is not active.
Exceptions
DOMException SYNTAX_ERR: The element was not defined with the appropriate syntax to allow endElement calls.
No Parameters

 

endElementAt
Causes this element to end the local timeline at the specified offset from the current time when the method is called.
Parameters
float offset The offset in seconds at which to end the element. Must be >= 0.
Return Value
boolean true if the method call was successful and the element was ended. false if method call failed. Possible reasons for failure include:
  • The element doesn't support the endElementAt method. (the end attribute is not set to "indefinite")
  • The element is not active.
Exceptions
DOMException SYNTAX_ERR: The element was not defined with the appropriate syntax to allow endElementAt calls.

 

Interface TimeEvent
The TimeEvent interface provides specific contextual information associated with Time events.

IDL Definition
interface TimeEvent : events::Event {
  readonly attribute views::AbstractView  view;
  readonly attribute long             detail;
  void               initTimeEvent(in DOMString typeArg, 
                                   in views::AbstractView viewArg, 
                                   in long detailArg);
};


Attributes
view of type views::AbstractView, readonly
The view attribute identifies the AbstractView from which the event was generated.

 

detail of type long, readonly
Specifies some detail information about the Event, depending on the type of event.

 

Methods
initTimeEvent
The initTimeEvent method is used to initialize the value of a TimeEvent created through the DocumentEvent interface. This method may only be called before the TimeEvent has been dispatched via the dispatchEvent method, though it may be called multiple times during that phase if necessary. If called multiple times, the final invocation takes precedence.
Parameters
DOMString typeArg Specifies the event type.
views::AbstractView viewArg Specifies the Event's AbstractView.
long detailArg Specifies the Event's detail.
No Return Value
No Exceptions

 

The different types of events that can occur are:

begin
This event is raised when the element local timeline begins to play. It will be raised each time the element begins the active duration (i.e. when it restarts, but not when it repeats). It may be raised both in the course of normal (i.e. scheduled or interactive) timeline play, as well as in the case that the element was begun with the beginElement() or beginElementAt() methods. Note that if an element is restarted while it is currently playing, the element will raise an end event and another begin event, as the element restarts.
  • Bubbles: No
  • Cancelable: No
  • Context Info: None
end
This event is raised at the active end of the element. Note that this event is not raised at the simple end of each repeat. This event may be raised both in the course of normal (i.e. scheduled or interactive) timeline play, as well as in the case that the element was ended with the endElement() or endElementAt() methods. Note that if an element is restarted while it is currently playing, the element will raise an end event and another begin event, as the element restarts.
  • Bubbles: No
  • Cancelable: No
  • Context Info: None
repeat
This event is raised when the element local timeline repeats. It will be raised each time the element repeats, after the first iteration.
The event provides a numerical indication of which repeat iteration is beginning. The value is a 0-based integer, but the repeat event is not raised for the first iteration and so the observed values of the detail attribute will be >= 1.
  • Bubbles: No
  • Cancelable: No
  • Context Info: detail (current iteration)

6.3. IDL definition

smil.idl:

// File: smil.idl
#ifndef _SMIL_IDL_
#define _SMIL_IDL_

#include "dom.idl"

#pragma prefix "dom.w3c.org"
module smil
{
  typedef dom::DOMString DOMString;

  interface ElementTimeControl {
    boolean            beginElement()
                                        raises(dom::DOMException);
    boolean            beginElementAt(in float offset)
                                        raises(dom::DOMException);
    boolean            endElement()
                                        raises(dom::DOMException);
    boolean            endElementAt(in float offset)
                                        raises(dom::DOMException);
  };

  interface TimeEvent : events::Event {
    readonly attribute views::AbstractView  view;
    readonly attribute long             detail;
    void               initTimeEvent(in DOMString typeArg, 
                                     in views::AbstractView viewArg, 
                                     in long detailArg);
  };
};

#endif // _SMIL_IDL_

6.4. Java language binding

org/w3c/dom/smil/ElementTimeControl.java:

package org.w3c.dom.smil;

import org.w3c.dom.DOMException;

public interface ElementTimeControl {
    public boolean beginElement()
                                throws DOMException;

    public boolean beginElementAt(float offset)
                                  throws DOMException;

    public boolean endElement()
                              throws DOMException;

    public boolean endElementAt(float offset)
                                throws DOMException;

}

org/w3c/dom/smil/TimeEvent.java:

package org.w3c.dom.smil;

import org.w3c.dom.events.Event;
import org.w3c.dom.views.AbstractView;

public interface TimeEvent extends Event {
    public AbstractView getView();

    public int getDetail();

    public void initTimeEvent(String typeArg, 
                              AbstractView viewArg, 
                              int detailArg);

}

6.5. ECMAScript language binding

Object ElementTimeControl
The ElementTimeControl object has the following methods:
beginElement()
This method returns a boolean.
beginElementAt(offset)
This method returns a boolean. The offset parameter is of type float.
endElement()
This method returns a boolean.
endElementAt(offset)
This method returns a boolean. The offset parameter is of type float.
Object TimeEvent
TimeEvent has the all the properties and methods of Event as well as the properties and methods defined below.
The TimeEvent object has the following properties:
view
This property is of type AbstractView.
detail
This property is of type long.
The TimeEvent object has the following methods:
initTimeEvent(typeArg, viewArg, detailArg)
This method returns a void. The typeArg parameter is of type DOMString. The viewArg parameter is of type views::AbstractView. The detailArg parameter is of type long.


 

7. Appendix: Differences from SMIL 1.0 timing model

8. References

[CSS2]
"Cascading Style Sheets, level 2", B. Bos, H. W. Lie, C. Lilley, I. Jacobs, 12 May 1998.
Available at http://www.w3.org/TR/REC-CSS2.
[DOM-Level-2]
"Document Object Model (DOM) Level 2 Specification"
Available at http://www.w3.org/TR/DOM-Level-2/.
[DOM2Events]
"Document Object Model Events", T. Pixley
Available at http://www.w3.org/TR/WD-DOM-Level-2/events.html.
[HTML]
"HTML 4.0 Specification", D. Raggett, A. Le Hors, I. Jacobs, 24 April 1998.
Available at http://www.w3.org/TR/REC-html40.
[SMIL1.0]
"Synchronized Multimedia Integration Language (SMIL) 1.0 Specification W3C Recommendation 15-June-1998 ".
Available at: http://www.w3.org/TR/REC-smil.
[SMIL-MOD]
"Synchronized Multimedia Modules based upon SMIL 1.0", Patrick Schmitz, Ted Wugofski, Warner ten Kate.
Available at http://www.w3.org/TR/NOTE-SYMM-modules.
[SVG]
"Scalable Vector Graphics (SVG) 1.0 Specification", W3C Working Draft.
Available at http://www.w3.org/TR/SVG/.
[XLink]
"XML Linking Language (XLink)", S. DeRose, D. Orchard, B. Trafford, editors, 9 July 1999.
Available at http://www.w3.org/TR/WD-xlink
[XML]
"Extensible Markup Language (XML) 1.0", T. Bray, J. Paoli, C.M. Sperberg-McQueen, editors, 10 February 1998.
Available at http://www.w3.org/TR/REC-xml
[XML-NS]
"Namespaces in XML" T. Bray, D. Hollander, A. Layman, editors, 14 January 1999.
Available at http://www.w3.org//TR/REC-xml-names/.