1 Introduction to SVG
1.1 About SVG
This specification defines the features and syntax for
Scalable Vector Graphics (SVG).
SVG is a language for describing two-dimensional graphics in XML. SVG allows
for three types of graphic objects: vector graphic shapes (e.g., paths consisting
of straight lines and curves), images and text.
Graphical objects can be grouped, styled, transformed and composited
into previously rendered objects.
The feature set includes nested transformations, clipping paths, alpha masks,
filter effects and template objects.
SVG drawings can be interactive and dynamic. Animations
can be defined and triggered either declaratively (i.e., by embedding SVG animation
elements in the SVG document) or via scripting.
Sophisticated applications of SVG are possible by use of
supplemental scripting language with access to SVG's
Document Object Model (DOM), which provides complete access to all elements,
attributes and properties. A rich set of event handlers such
as onmouseover and onclick can be assigned to any SVG graphical object.
Because of its compatibility and leveraging of other Web standards,
features like scripting can be done on XHTML and SVG elements simultaneously
within the same Web page.
1.2 SVG MIME Type
The MIME type for SVG will be "image/svg". The W3C will register this
MIME type around the time which SVG is approved as a W3C Recommendation.
1.3 Compatibility with Other Standards Efforts
SVG leverages and integrates with other W3C specifications and standards efforts.
By leveraging and conforming to other standards, SVG becomes more powerful and
makes it easier for users to learn how to incorporate SVG into their Web sites.
The following describes some of the ways in which SVG maintains compatibility
with, leverages and integrates with other W3C efforts:
- SVG is an application of XML and is compatible with
the "Extensible Markup Language (XML) 1.0" Recommendation
[XML10]
- SVG is compatible with the "Namespaces in XML" Recommendation
[XML-NS]
- SVG is tracking and will conform with
"XML Linking Language (XLink)"
[XLINK] and
"XML Pointer Language (XPointer)"
[XPTR]
(once these
specifications become Recommendations)
- SVG supports many of the properties and approaches described
in the "Cascading Style Sheets (CSS) level 2" specification
[CSS2].
(See SVG's Use of Cascading Style Sheets.)
- External style sheets are referenced using the mechanism documented
in "Associating Style Sheets with XML documents Version 1.0"
[ESS].
- SVG includes a complete Document Object Model (DOM)
and conforms to the "Document Object Model
(DOM) level 1" Recommendation
[DOM1].
The SVG DOM has a high level of compatibility and consistency
with the HTML DOM that is defined in the DOM level 1 specification.
Additionally, the SVG DOM is tracking and incorporating many of the facilities
described in latest drafts of "Document Object Model
(DOM) level 2"
[DOM2],
including the approach to the CSS object model and event handling.
- SVG incorporates some features and approaches that are part of the
"Synchronized Multimedia Integration Language (SMIL) 1.0 Specification"
[SMIL1], including
the <switch> element,
the test attribute and
the timing attributes that are within SVG's animation elements
(see Animation). SVG's animation
facility was developed with an attempt toward compatibility
with work-in-progress efforts towards formulating
SMIL 2.0.
- SVG attempts to achieve maximum compatibility with both
the "HTML 4.0 Specification"
[HTML40] and
the most recent working drafts of
"XHTML(tm) 1.0: The Extensible HyperText Markup Language"
[XHTML10].
Many of SVG's facilities are modeled directly after
HTML, including its use of
CSS [CSS2],
its approach to event handling,
its approach to its Document Object Model [DOM1].
- SVG is compatibility with W3C work
on internationalization.
References (W3C and otherwise) include:
[UNICODE],
[UNICODE21] and
[CHARMOD].
Also, see Internationalization Support.
- SVG is compatibility with W3C work
on web accessibility
[ACCESS].
Also, see Accessibility Support.
Because SVG conforms to DOM, it will be scriptable just like HTML version 4
(sometimes called DHTML).
This will allow a single scripting approach to be used simultaneously for both
XML documents and SVG graphics.
Thus, interactive and dynamic effects will be possible on multiple XML namespaces
using the same set of scripts.
1.4 Terminology
- basic shape
- Standard shapes which are predefined in SVG as a convenience
for common graphical operations. Specifically:
<rect>,
<circle>,
<ellipse>,
<line>,
<polyline>,
<polygon>,
- canvas
- a surface onto which graphics elements are drawn, which
can be real physical media such as a display or paper or
an abstract surface such as a allocated region of computer memory.
See the discussion of the SVG document canvas
in the chapter on Coordinate Systems, Transformations and Units.
- clipping path
- a combination of
<path>,
<text> and
basic shapes
which serve as the outline of a (in the absense of antialiasing) 1-bit mask,
where everything on the "inside" of the outline is allowed to show through
but everything on the outside is masked out.
See Clipping paths.
- container element
- An element which can have graphics elements and other container
elements as child elements. Specifically:
<svg>,
<g>,
<defs>
<symbol>,
<clipPath>,
<mask>,
<pattern>,
<marker>,
<a> and
<switch>.
- current transformation matrix (CTM)
- Transformation matrices define the mathematical mapping
from one coordinate system into another using
a 3x3 matrix using the equation
[x' y' 1] = [x y 1] * matrix.
The current transformation matrix (CTM)
defines the mapping from the user coordinate system into
the viewport coordinate system.
See
Establishing A New User Coordinate System: Transformations
- fill
- The operation of painting
the interior of a shape or
the interior of the character glyphs in a text string.
- graphics element
- One of the element types that can cause graphics to be drawn
onto the target canvas. Specifically:
<path>,
<text>,
<rect>,
<circle>,
<ellipse>,
<line>,
<polyline>,
<polygon>,
<image> and
<use>.
- graphics referencing element
- A graphics element which uses a reference to a different document
or element as the source of its graphical content. Specifically:
<use> and
<image>.
- local URI reference
- A Uniform Resource Identifier [URI]
that does not include an <absoluteURI> or
<relativeURI> and thus represents
a reference to an element/fragment within the current document.
See References and the <defs> element.
- mask
- a
container element
which can contain
graphics elements or
other container elements which define a set of graphics that
is to be used as a semi-transparent
mask for compositing foreground objects into the current background.
See Masks.
- non-local URI reference
- A Uniform Resource Identifier [URI]
that includes an <absoluteURI> or
<relativeURI> and thus (usually) represents
a reference to a different document or an element/fragment
within a different document.
See References and the <defs> element.
- number
- A real number (??? provide exact BNF)
- paint
- A paint represents a way of putting color values onto the canvas. A paint might consists
of both color values and associated alpha values
which control the blending of colors against already existing color values on the canvas.
SVG supports three types of built-in paint: color,
gradients and patterns.
- shape
- A graphics element that is defined by some combination of straight lines
and curves. Specifically:
<path>,
<rect>,
<circle>,
<ellipse>,
<line>,
<polyline>,
<polygon>,
- stroke
- The operation of painting
the outline of a shape or
the outline of character glyphs in a text string.
- SVG document canvas
- the canvas onto which the SVG document is rendered.
See the discussion of the SVG document canvas
in the chapter on Coordinate Systems, Transformations and Units.
- SVG document viewport
- the viewport
within the SVG document canvas which
defines the rectangular region into which the SVG document is rendered.
See the discussion of the SVG document viewport
in the chapter on Coordinate Systems, Transformations and Units.
- transformation
- A modification of the
current transformation matrix (CTM)
by providing a supplemental transformation in the form of
a set of simple transformations specifications (such as
scaling, rotation or translation) and/or one or more
transformation matrices.
See
Establishing A New User Coordinate System: Transformations
- transformation matrix
- Transformation matrices define the mathematical mapping
from one coordinate system into another using
a 3x3 matrix using the equation
[x' y' 1] = [x y 1] * matrix.
See current transformation matrix (CTM)
and
Establishing A New User Coordinate System: Transformations
- URI Reference
- A Uniform Resource Identifier [URI]
which serves as a reference to a file or to an element/fragment within a file.
See References and the <defs> element.
- user coordinate system
- In general, a coordinate system defines locations and distances
on the current canvas.
The current user coordinate system
is the coordinate system that is currently active and which is used to
define how coordinates and lengths are located and computed, respectively,
on the current canvas.
See initial user coordinate system
and Establishing A New User Coordinate System: Transformations.
- user space
- A synonym for user coordinate system.
- user units
- A coordinate value or length expressed in user units represents a coordinate
value or length in the current
user coordinate system.
Thus, 10 user units represents a length of 10 units in the
current user coordinate system.
- viewport
- a rectangular region within the current canvas
onto which graphics elements are to be rendered.
See the discussion of the SVG document viewport
in the chapter on Coordinate Systems, Transformations and Units.
- viewport coordinate system
- In general, a coordinate system defines locations and distances
on the current canvas.
The viewport coordinate system
is the coordinate system that is active at the start of processing
of an
<svg> element, before
processing the optional
fitBoxToViewport attribute.
In the case of an SVG document that is embedded within a parent
document which uses CSS to manage its layout, then the viewport
coordinate system will have the same orientation and lengths
as in CSS, with the origin at the top-left
on the viewport.
See Establishing the initial viewport
and Establishing a New Viewport: the <svg> element within an SVG document.
- viewport space
- A synonym for viewport coordinate system.
- viewport units
- A coordinate value or length expressed in viewport units represents a coordinate
value or length in the
viewport coordinate system.
Thus, 10 viewport units represents a length of 10 units in the
viewport coordinate system.