11 Painting: Filling, Stroking and Marker Symbols

Contents

• 11.1 Introduction
• 11.2 Specifying paint
• 11.3 Fill Properties
• 11.4 Stroke Properties
• 11.5 Controlling visibility
• 11.6 Markers
  • 11.6.1 Introduction
  • 11.6.2 The 'marker' element
  • 11.6.3 Marker properties
  • 11.6.4 Details on how markers are rendered
• 11.7 Rendering properties
  • 11.7.1 Color interpolation properties: 'color-interpolation' and 'color-interpolation-filters'
  • 11.7.2 The 'color-rendering' property
  • 11.7.3 The 'shape-rendering' property
  • 11.7.4 The 'text-rendering' property
  • 11.7.5 The 'image-rendering' property
• 11.8 Inheritance of painting properties
• 11.9 Full Paint Attribute Module
• 11.10 Tiny Paint Attribute Module
• 11.11 Full Opacity Attribute Module
• 11.12 Full Graphics Attribute Module
• 11.13 Tiny Graphics Attribute Module
• 11.14 Full Marker Module
• 11.15 DOM interfaces

11.1 Introduction

'path' elements, 'text' elements and basic shapes can be filled (which means painting the interior of the object) and stroked (which means painting along the outline of the object). Filling and stroking both can be thought of in more general terms as painting operations.

Certain elements (i.e., 'path', 'polyline', 'polygon' and 'line' elements) can also have marker symbols drawn at their vertices.

With SVG, you can paint (i.e., fill or stroke) with:

• a single color
• a solid color with opacity
• a gradient (linear or radial)
• a pattern (vector or image, possibly tiled)
• custom paints available via extensibility

SVG uses the general notion of a paint server. Paint servers are specified using a URI reference on a 'fill' or 'stroke' property. Gradients, patterns and solid colors are just specific types of paint servers.

11.2 Specifying paint

Properties 'fill' and 'stroke' take on a value of type <paint>, which is specified as follows:

none

Indicates that no paint is applied.

currentColor

Indicates that painting is done using the color specified by the 'color' property. This mechanism is provided to facilitate sharing of color attributes between parent grammars such as other (non-SVG) XML. This mechanism allows you to define a style in your HTML which sets the 'color' property and then pass that style to the SVG user agent so that your SVG text will draw in the same color.

<color> [icc-color(<name>[,<icccolorvalue>]*)]

<color> is the explicit color (in the sRGB [SRGB] color space) to be used to paint the current object. SVG supports all of the syntax alternatives for <color> defined in [ CSS2-color-types], with the exception that SVG contains an expanded list of recognized color keywords names. If an optional ICC color specification is provided, then the user agent searches the color profile description database for a color profile description entry whose name descriptor matches <name> and uses the last matching entry that is found. (If no match is found, then the ICC color specification is ignored.) The comma-separated list (with optional white space) of <icccolorvalue>'s is a set of ICC-profile-specific color values, expressed as <number>s. (In most cases, the <icccolorvalue>'s will be in the range 0-to-1.) On platforms which support ICC-based color management, the icc-color gets precedence over the <color> (which is in the sRGB color space). Note that color interpolation occurs in an RGB color space even if an ICC-based color specification is provided (see 'color-interpolation' and 'color-interpolation-filters'). Percentages are not allowed on <icccolorvalue>'s. For more on ICC-based colors, refer to Color profile descriptions.

<uri>
   [ none |
      currentColor |
      <color> [icc-color(<name>[,<icccolorvalue>]*)]

The <uri> is how you identify a paint server such as a gradient, a pattern or a custom paint defined by an extension (see Extensibility). The <uri> provides the ID of the paint server (e.g., a gradient, pattern or solid color) to be used to paint the current object. If the URI reference is not valid (e.g., it points to an object that doesn't exist or the object is not a valid paint server), then the paint method following the <uri> (i.e., none | currentColor | <color> [icc-color(<name>[,<icccolorvalue>]*)]| inherit) is used if provided; otherwise, the document is in error (see Error processing).

11.3 Fill Properties

The 'fill' property paints the interior of the given graphical element. The area to be painted consists of any areas inside the outline of the shape. To determine the inside of the shape, all subpaths are considered, and the interior is determined according to the rules associated with the current value of the 'fill-rule' property. The zero-width geometric outline of a shape is included in the area to be painted.

The fill operation fills open subpaths by performing the fill operation as if an additional "closepath" command were added to the path to connect the last point of the subpath with the first point of the subpath. Thus, fill operations apply to both open subpaths within 'path' elements (i.e., subpaths without a closepath command) and 'polyline' elements.

The 'fill-rule' property indicates the algorithm which is to be used to determine what parts of the canvas are included inside the shape. For a simple, non-intersecting path, it is intuitively clear what region lies "inside"; however, for a more complex path, such as a path that intersects itself or where one subpath encloses another, the interpretation of "inside" is not so obvious.

The 'fill-rule' property provides two options for how the inside of a shape is determined:

nonzero

This rule determines the "insideness" of a point on the canvas by drawing a ray from that point to infinity in any direction and then examining the places where a segment of the shape crosses the ray. Starting with a count of zero, add one each time a path segment crosses the ray from left to right and subtract one each time a path segment crosses the ray from right to left. After counting the crossings, if the result is zero then the point is outside the path. Otherwise, it is inside. The following drawing illustrates the nonzero rule:

View this example as SVG (SVG-enabled browsers only)
 

evenodd

This rule determines the "insideness" of a point on the canvas by drawing a ray from that point to infinity in any direction and counting the number of path segments from the given shape that the ray crosses. If this number is odd, the point is inside; if even, the point is outside. The following drawing illustrates the evenodd rule:

View this example as SVG (SVG-enabled browsers only)
 

(Note: the above explanations do not specify what to do if a path segment coincides with or is tangent to the ray. Since any ray will do, one may simply choose a different ray that does not have such problem intersections.)

'fill-opacity' specifies the opacity of the painting operation used to paint the interior the current object. (See Painting shapes and text.)

<opacity-value>

The opacity of the painting operation used to fill the current object. Any values outside the range 0.0 (fully transparent) to 1.0 (fully opaque) will be clamped to this range. (See Clamping values which are restricted to a particular range.)

Related properties: 'stroke-opacity' and 'opacity'.

11.4 Stroke Properties

The following are the properties which affect how an element is stroked.

In all cases, all stroking properties which are affected by directionality, such as those having to do with dash patterns, must be rendered such that the stroke operation starts at the same point at which the graphics element starts. In particular, for 'path' elements, the start of the path is the first point of the initial "moveto" command.

For stroking properties such as dash patterns whose computations are dependent on progress along the outline of the graphics element, distance calculations are required to utilize the SVG user agent's standard Distance along a path algorithms.

When stroking is performed using a complex paint server, such as a gradient or a pattern, the stroke operation must be identical to the result that would have occurred if the geometric shape defined by the geometry of the current graphics element and its associated stroking properties were converted to an equivalent 'path' element and then filled using the given paint server.

The 'stroke' property paints along the outline of the given graphical element.

A subpath (see Paths) consisting of a single moveto is not stroked. A subpath consisting of a moveto and lineto to the same exact location or a subpath consisting of a moveto and a closepath will be stroked only if the 'stroke-linecap' property is set to "round", producing a circle centered at the given point.

<length>

The width of the stroke on the current object. If a percentage is used, the value represents a percentage of the current viewport. (See Units.)
A zero value causes no stroke to be painted. A negative value is an error (see Error processing).

'stroke-linecap' specifies the shape to be used at the end of open subpaths when they are stroked.

butt

See drawing below.

round

See drawing below.

square

See drawing below.

View this example as SVG (SVG- and CSS-enabled browsers only)
 

'stroke-linejoin' specifies the shape to be used at the corners of paths or basic shapes when they are stroked.

miter

See drawing below.

round

See drawing below.

bevel

See drawing below.

View this example as SVG (SVG- and CSS-enabled browsers only)
 

When two line segments meet at a sharp angle and miter joins have been specified for 'stroke-linejoin', it is possible for the miter to extend far beyond the thickness of the line stroking the path. The 'stroke-miterlimit' imposes a limit on the ratio of the miter length to the 'stroke-linewidth'.

<miterlimit>

The limit on the ratio of the miter length to the 'stroke-linewidth'. The value of <miterlimit> must be a number greater than or equal to 1. Any other value is an error (see Error processing).

'stroke-dasharray' controls the pattern of dashes and gaps used to stroke paths. <dasharray> contains a list of comma-separated (with optional white space) <length>s that specify the lengths of alternating dashes and gaps. If an odd number of values is provided, then the list of values is repeated to yield an even number of values. Thus, stroke-dasharray: 5,3,2 is equivalent to stroke-dasharray: 5,3,2,5,3,2.

none

Indicates that no dashing is used. If stroked, the line is drawn solid.

<dasharray>

A list of comma-separated <length>'s (with optional white space), each of which can have a unit identifier , including specification of a percentage. A percentage represents a distance as a percentage of the current viewport. (See Units.) A negative <length> value is an error (see Error processing). If the sum of the <length>'s is zero, then the stroke is rendered as if a value of none were specified.

'stroke-dashoffset' specifies the distance into the dash pattern to start the dash.

<length>

If a percentage is used, the value represents a percentage of the current viewport
(See Units.)
Values can be negative.

'stroke-opacity' specifies the opacity of the painting operation used to stroke the current object. (See Painting shapes and text.)

<opacity-value>

The opacity of the painting operation used to stroke the current object. Any values outside the range 0.0 (fully transparent) to 1.0 (fully opaque) will be clamped to this range. (See Clamping values which are restricted to a particular range.)

Related properties: 'fill-opacity' and 'opacity'.

11.5 Controlling visibility

SVG uses two properties, 'display' and 'visibility', to control the visibility of graphical elements or (in the case of the 'display' property) container elements.

The differences between the two properties are as follows:

• When applied to a container element, setting 'display' to none causes the container and all of its children to be invisible; thus, it acts on groups of elements as a group. 'visibility', however, only applies to individual graphics elements. Setting 'visibility' to hidden on a 'g' will make its children invisible as long as the children do not specify their own 'visibility' properties as visible. Note that 'visibility' is not an inheritable property.
• When the 'display' property is set to none, then the given element does not become part of the rendering tree. With 'visibility' set to hidden, however, processing occurs as if the element were part of the rendering tree and still taking up space, but not actually rendered onto the canvas. This distinction has implications for the 'tspan', 'tref' and 'altGlyph' elements, event processing, for bounding box calculations and for calculation of clipping paths. If 'display' is set to none on a 'tspan', 'tref' or 'altGlyph' element, then the text string is ignored for the purposes of text layout; however, if 'visibility' is set to hidden, the text string is used for text layout (i.e., it takes up space) even though it is not rendered on the canvas. Regarding events, if 'display' is set to none, the element receives no events; however, if 'visibility' is set to hidden, the element might still receive events, depending on the value of property 'pointer-events'. The geometry of a graphics element with 'display' set to none is not included in bounding box and clipping paths calculations; however, even if 'visibility' is to hidden, the geometry of the graphics element still contributes to bounding box and clipping path calculations.

A value of display: none indicates that the given element and its children shall not be rendered directly (i.e., those elements are not present in the rendering tree). Any value other than none or inherit indicates that the given element shall be rendered by the SVG user agent.

The 'display' property only affects the direct rendering of a given element, whereas it does not prevent elements from being referenced by other elements. For example, setting display: none on a 'path' element will prevent that element from getting rendered directly onto the canvas, but the 'path' element can still be referenced by a 'textPath' element; furthermore, its geometry will be used in text-on-a-path processing even if the 'path' has display: none.

The 'display' property affects direct rendering into offscreen canvases also, such as occurs with the implementation model for masks. Thus, setting display: none on a child of a 'mask' will prevent the given child element from being rendered as part of the mask. Similarly, setting display: none on a child of a 'clipPath' element will prevent the given child element from contributing to the clipping path.

Elements with display: none do not take up space in text layout operations, do not receive events, and do not contribute to bounding box and clipping paths calculations.

Except for any additional information provided in this specification, the normative definition is the CSS2 definition of the 'display' property.

visible

The current graphics element is visible.

hidden or collapse

The current graphics element is invisible (i.e., nothing is painted on the canvas).

Note that if the 'visibility' property is set to hidden on a 'tspan', 'tref' or 'altGlyph' element, then the text is invisible but still takes up space in text layout calculations.

Depending on the value of property 'pointer-events', graphics elements which have their 'visibility' property set to hidden still might receive events.

Except for any additional information provided in this specification, the normative definition is the CSS2 definition of the 'visibility' property.

11.6 Markers

11.6.1 Introduction

A marker is a symbol which is attached to one or more vertices of 'path', 'line', 'polyline' and 'polygon' elements. Typically, markers are used to make arrowheads or polymarkers. Arrowheads can be defined by attaching a marker to the start or end vertices of 'path', 'line' or 'polyline' elements. Polymarkers can be defined by attaching a marker to all vertices of a 'path', 'line', 'polyline' or 'polygon' element.

The graphics for a marker are defined by a 'marker' element. To indicate that a particular 'marker' element should be rendered at the vertices of a particular 'path', 'line', 'polyline' or 'polygon' element, set one or more marker properties ('marker', 'marker-start', 'marker-mid' or 'marker-end') to reference the given 'marker' element.

Example Marker draws a triangular marker symbol as an arrowhead at the end of a path.

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
  "http://www.w3.org/TR/2002/WD-SVG11-20020215/DTD/svg11.dtd">
<svg width="4in" height="2in" 
     viewBox="0 0 4000 2000" version="1.1"
     xmlns="http://www.w3.org/2000/svg">
  <defs>
    <marker id="Triangle"
      viewBox="0 0 10 10" refX="0" refY="5" 
      markerUnits="strokeWidth"
      markerWidth="4" markerHeight="3"
      orient="auto">
      <path d="M 0 0 L 10 5 L 0 10 z" />
    </marker>
  </defs>
  <rect x="10" y="10" width="3980" height="1980"
       fill="none" stroke="blue" stroke-width="10" />
  <desc>Placing an arrowhead at the end of a path.
  </desc>
  <path d="M 1000 750 L 2000 750 L 2500 1250"
        fill="none" stroke="black" stroke-width="100" 
        marker-end="url(#Triangle)"  />
</svg>

Example Marker

View this example as SVG (SVG-enabled browsers only)
 

Markers can be animated. The animated effects will show on all current uses of the markers within the document.

11.6.2 The 'marker' element

The 'marker' element defines the graphics that is to be used for drawing arrowheads or polymarkers on a given 'path', 'line', 'polyline' or 'polygon' element.
 

<!ENTITY % markerExt "" >
<!ELEMENT marker (desc|title|metadata|defs|
                   path|text|rect|circle|ellipse|line|polyline|polygon|
                   use|image|svg|g|view|switch|a|altGlyphDef|
                   script|style|symbol|marker|clipPath|mask|
                   linearGradient|radialGradient|pattern|filter|cursor|font|
                   animate|set|animateMotion|animateColor|animateTransform|
                   color-profile|font-face
                   %ceExt;%markerExt;)* >
<!ATTLIST marker
  %stdAttrs;
  %langSpaceAttrs;
  externalResourcesRequired %Boolean; #IMPLIED
  class %ClassList; #IMPLIED
  style %StyleSheet; #IMPLIED
  %PresentationAttributes-All;
  viewBox %ViewBoxSpec; #IMPLIED
  preserveAspectRatio %PreserveAspectRatioSpec; 'xMidYMid meet'
  refX %Coordinate; #IMPLIED
  refY %Coordinate; #IMPLIED
  markerUnits (strokeWidth | userSpaceOnUse) #IMPLIED
  markerWidth  %Length; #IMPLIED
  markerHeight %Length; #IMPLIED
  orient CDATA #IMPLIED >

Markers are drawn such that their reference point (i.e., attributes refX and refY) is positioned at the given vertex. In other words, a translation transformation is constructed by the user agent to achieve the effect of having point (refX and refY) within the marker content's coordinate system (after any transformations due to the viewBox and preserveAspectRatio attributes) align exactly with the given vertex.

SVG's user agent style sheet sets the 'overflow' property for 'marker' elements to hidden, which causes a rectangular clipping path to be created at the bounds of the marker tile. Unless the 'overflow' property is overridden, any graphics within the marker which goes outside of the marker rectangle will be clipped.

The contents of the 'marker' are relative to a new coordinate system. Attribute markerUnits determines an initial scale factor for transforming the graphics in the marker into the user coordinate system for the referencing element. An additional set of transformations might occur if there is a viewBox attribute, in which case the coordinate system for the contents of the 'marker' will be transformed due to the processing of attributes viewBox and preserveAspectRatio. If there is no viewBox attribute, then the assumed default value for the the viewBox attribute has the origin of the viewBox coincident with the origin of the viewport and the width/height of the viewBox the same as the width/height of the viewport.

Properties inherit into the 'marker' element from its ancestors; properties do not inherit from the element referencing the 'marker' element.

'marker' elements are never rendered directly; their only usage is as something that can be referenced using the 'marker', 'marker-start', 'marker-end' and 'marker-mid' properties. The 'display' property does not apply to the 'marker' element; thus, 'marker' elements are not directly rendered even if the 'display' property is set to a value other than none, and 'marker' elements are available for referencing even when the 'display' property on the 'marker' element or any of its ancestors is set to none.

Event attributes and event listeners attached to the contents of a 'marker' element are not processed; only the rendering aspects of 'marker' elements are processed.

11.6.3 Marker properties

'marker-start' defines the arrowhead or polymarker that shall be drawn at the first vertex of the given 'path' element or basic shape. 'marker-end' defines the arrowhead or polymarker that shall be drawn at the final vertex. 'marker-mid' defines the arrowhead or polymarker that shall be drawn at every other vertex (i.e., every vertex except the first and last). Note that for a 'path' element which ends with a closed sub-path, the last vertex is the same as the initial vertex on the given sub-path. In this case, if 'marker-end' does not equal none, then it is possible that two markers will be rendered on the given vertex. One way to prevent this is to set 'marker-end' to none. (Note that the same comment applies to 'polygon' elements.)

none

Indicates that no marker symbol shall be drawn at the given vertex (vertices).

<uri>

The <uri> is a URI reference to the 'marker' element which shall be used as the arrowhead symbol or polymarker at the given vertex or vertices. If the URI reference is not valid (e.g., it points to an object that is undefined or the object is not a 'marker' element), then the marker(s) shall not be drawn.

The 'marker' property specifies the marker symbol that shall be used for all points on the sets the value for all vertices on the given 'path' element or basic shape. It is a short-hand for the three individual marker properties:

11.6.4 Details on how markers are rendered

Markers are drawn after the given object is filled and stroked.

For each marker that is drawn, a temporary new user coordinate system is established so that the marker will be positioned and sized correctly, as follows:

• The axes of the temporary new user coordinate system are aligned according to the orient attribute on the 'marker' element and the slope of the curve at the given vertex. (Note: if there is a discontinuity at a vertex, the slope is the average of the slopes of the two segments of the curve that join at the given vertex. If a slope cannot be determined, the slope is assumed to be zero.)
• A temporary new coordinate system is established by attribute markerUnits. If markerUnits equals strokeWidth, then the temporary new user coordinate system is the result of scaling the current user coordinate system by the current value of property 'stroke-width'. If markerUnits equals userSpaceOnUse, then no extra scale transformation is applied.
• An additional set of transformations might occur if the 'marker' element includes a viewBox attribute, in which case additional transformations are set up to produce the necessary result due to attributes viewBox and preserveAspectRatio.
• If the 'overflow' property on the 'marker' element indicates that the marker needs to be clipped to its viewport, then an implicit clipping path is established at the bounds of the viewport.

The rendering effect of a marker is as if the contents of the referenced 'marker' element were deeply cloned into a separate non-exposed DOM tree for each instance of the marker. Because the cloned DOM tree is non-exposed, the SVG DOM does not show the cloned instance of the marker.

For user agents that support Styling with CSS, the conceptual deep cloning of the referenced 'marker' element into a non-exposed DOM tree also copies any property values resulting from the CSS cascade [CSS2-CASCADE] and property inheritance on the referenced element and its contents. CSS2 selectors can be applied to the original (i.e., referenced) elements because they are part of the formal document structure. CSS2 selectors cannot be applied to the (conceptually) cloned DOM tree because its contents are not part of the formal document structure.

For illustrative purposes, we'll repeat the marker example shown earlier:

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
  "http://www.w3.org/TR/2002/WD-SVG11-20020215/DTD/svg11.dtd">
<svg width="4in" height="2in" 
     viewBox="0 0 4000 2000" version="1.1"
     xmlns="http://www.w3.org/2000/svg">
  <defs>
    <marker id="Triangle"
      viewBox="0 0 10 10" refX="0" refY="5" 
      markerUnits="strokeWidth"
      markerWidth="4" markerHeight="3"
      orient="auto">
      <path d="M 0 0 L 10 5 L 0 10 z" />
    </marker>
  </defs>
  <rect x="10" y="10" width="3980" height="1980"
       fill="none" stroke="blue" stroke-width="10" />
  <desc>Placing an arrowhead at the end of a path.
  </desc>
  <path d="M 1000 750 L 2000 750 L 2500 1250"
        fill="none" stroke="black" stroke-width="100" 
        marker-end="url(#Triangle)"  />
</svg>

The rendering effect of the above file will be visually identical to the following:

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
  "http://www.w3.org/TR/2002/WD-SVG11-20020215/DTD/svg11.dtd">
<svg width="4in" height="2in" 
     viewBox="0 0 4000 2000" version="1.1"
     xmlns="http://www.w3.org/2000/svg">

  <desc>File which produces the same effect
      as the marker example file, but without
      using markers.
  </desc>
  <rect x="10" y="10" width="3980" height="1980"
       fill="none" stroke="blue" stroke-width="10" />
  <!-- The path draws as before, but without the marker properties -->
  <path d="M 1000 750 L 2000 750 L 2500 1250"
        fill="none" stroke="black" stroke-width="100"  />

  <!-- The following logic simulates drawing a marker 
       at final vertex of the path. -->

  <!-- First off, move the origin of the user coordinate system
       so that the origin is now aligned with the end point of the path. -->
  <g transform="translate(2500,1250)" >

    <!-- Rotate the coordinate system 45 degrees because
         the marker specified orient="auto" and the final segment
         of the path is going in the direction of 45 degrees. -->
    <g transform="rotate(45)" >

      <!-- Scale the coordinate system to match the coordinate system
           indicated by the 'markerUnits' attributes, which in this case has
           a value of 'strokeWidth'. Therefore, scale the coordinate system
           by the current value of the 'stroke-width' property, which is 100. -->
      <g transform="scale(100)" >

        <!-- Translate the coordinate system by 
             (-refX*viewBoxToMarkerUnitsScaleX, -refY*viewBoxToMarkerUnitsScaleY)
             in order that (refX,refY) within the marker will align with the vertex.
             In this case, we use the default value for preserveAspectRatio
             ('xMidYMid meet'), which means find a uniform scale factor
             (i.e., viewBoxToMarkerUnitsScaleX=viewBoxToMarkerUnitsScaleY)
             such that the viewBox fits entirely within the viewport ('meet') and 
             is center-aligned ('xMidYMid'). In this case, the uniform scale factor
             is markerHeight/viewBoxHeight=3/10=.3. Therefore, translate by
             (-refX*.3,-refY*.3)=(0*.3,-5*.3)=(0,-1.5). -->
        <g transform="translate(0,-1.5)" >

          <!-- There is an implicit clipping path because the user agent style
               sheet says that the 'overflow' property for markers has the value
               'hidden'. To achieve this, create a clipping path at the bounds
               of the viewport. Note that in this case the viewport extends
               0.5 units to the left and right of the viewBox due to 
               a uniform scale factor, different ratios for markerWidth/viewBoxWidth
               and markerHeight/viewBoxHeight, and 'xMidYMid' alignment -->
          <clipPath id="cp1" >
            <rect x="-0.5" y="0" width="4" height="3" />
          </clipPath>
          <g clip-path="url(#cp1)" >

            <!-- Scale the coordinate system by the uniform scale factor
                 markerHeight/viewBoxHeight=3/10=.3 to set the coordinate
                 system to viewBox units. -->
            <g transform="scale(.3)" >

              <!-- This 'g' element carries all property values that result from
                   cascading and inheritance of properties on the original 'marker' element.
                   In this example, neither fill nor stroke was specified on the 'marker'
                   element or any ancestors of the 'marker', so the initial values of
                   "black" and "none" are used, respectively. -->
             <g fill="black" stroke="none" >

                <!-- Expand out the contents of the 'marker' element. -->
                <path d="M 0 0 L 10 5 L 0 10 z" />
              </g>
            </g>
          </g>
        </g>
      </g>
    </g>
  </g>
</svg>

View this example as SVG (SVG-enabled browsers only)
 

11.7 Rendering properties

11.7.1 Color interpolation properties: 'color-interpolation' and 'color-interpolation-filters'

The SVG user agent performs color interpolations and compositing at various points as it processes SVG content. Two properties, 'color-interpolation' and 'color-interpolation-filters', control which color space is used for particular categories of graphics operations. The following table shows which property applies to which graphics operations:

Both properties choose between color operations occurring in the sRGB color space or in a (light energy linear) linearized RGB color space.

The conversion formulas between the sRGB color space (i.e., nonlinear with 2.2 gamma curve) and the linearized RGB color space (i.e., color values expressed as sRGB tristimulus values without a gamma curve) can be found in [SRGB]. For illustrative purposes, the following formula shows the conversion from sRGB to linearized RGB:

  R[sRGB] = R[sRGB-8bit] / 255
  G[sRGB] = G[sRGB-8bit] / 255
  B[sRGB] = B[sRGB-8bit] / 255

If R[sRGB], G[sRGB], B[sRGB] <= 0.04045

  R[linearRGB] = R[sRGB] / 12.92
  G[linearRGB] = G[sRGB] / 12.92
  B[linearRGB] = B[sRGB] / 12.92

else if R[sRGB], G[sRGB], B[sRGB] > 0.04045

  R[linearRGB] = ((R[sRGB] + 0.055) / 1.055) ^ 2.4
  G[linearRGB] = ((G[sRGB] + 0.055) / 1.055) ^ 2.4
  B[linearRGB] = ((B[sRGB] + 0.055) / 1.055) ^ 2.4

  R[linearRGB-8bit] = R[linearRGB] * 255
  G[linearRGB-8bit] = G[linearRGB] * 255
  B[linearRGB-8bit] = B[linearRGB] * 255

Out-of-range color values, if supported by the user agent, also are converted using the above formulas. (See Clamping values which are restricted to a particular range.)

auto

Indicates that the user agent can choose either the sRGB or linearRGB spaces for color interpolation. This option indicates that the author doesn't require that color interpolation occur in a particular color space.

sRGB

Indicates that color interpolation should occur in the sRGB color space.

linearRGB

Indicates that color interpolation should occur in the linearized RGB color space as described above.

The 'color-interpolation' property specifies the color space for gradient interpolations, color animations and alpha compositing.

When a child element is blended into a background, the value of the 'color-interpolation' property on the child determines the type of blending, not the value of the 'color-interpolation' on the parent. For gradients which make use of the xlink:href attribute to reference another gradient, the gradient uses the 'color-interpolation' property value from the gradient element which is directly referenced by the 'fill' or 'stroke' property. When animating colors, color interpolation is performed according to the value of the 'color-interpolation' property on the element being animated.