A path represents the outline of a shape which can be filled or stroked. A path can also be used as a clipping path, to describe animation, or position text. A path can be used for more than one of these functions at the same time. (See Filling, Stroking and Paint Servers, Clipping and Masking, Animation ('animateMotion'), and Text on a Path.)
A path is described using the concept of a current point. In an analogy with drawing on paper, the current point can be thought of as the location of the pen. The position of the pen can be changed, and the outline of a shape (open or closed) can be traced by dragging the pen in either straight lines or curves.
Paths represent the geometry of the outline of an object, defined in terms of moveto (set a new current point), bearing (set a new orientation), lineto (draw a straight line), curveto (draw a curve using a cubic Bézier), arc (elliptical or circular arc) and closepath (close the current shape by connecting to the last moveto) commands. Compound paths (i.e., a path with multiple subpaths) are possible to allow effects such as "donut holes" in objects.
This chapter describes the syntax, behavior and DOM interfaces for SVG paths. Various implementation notes for SVG paths can be found in ‘path’ element implementation Notes and Elliptical arc implementation notes.
A path is defined in SVG using the ‘path’ element.
The basic shapes are all described in terms of what their equivalent path is, which is what their shape is as a path. (The equivalent path of a ‘path’ element is simply the path itself.)
The outline of a shape for a ‘path’ element is specified using the d property. See Path data below.
| SVG 2 Requirement: | Support turtle-graphics-like current rotation in path syntax. |
|---|---|
| Resolution: | We will add a path rotation command. |
| Purpose: | Make path rotations easier to animate and pie charts easier to draw. |
| Owner: | Cameron (ACTION-3125) |
| Status: | Done |
A path is defined by including a ‘path’ element on which the d property specifies the path data. The path data contains the moveto, bearing, lineto, curveto (both cubic and quadratic Béziers), arc and closepath instructions.
Example triangle01 specifies a path in the shape of a triangle. (The M indicates a moveto, the Ls indicate linetos, and the z indicates a closepath).
<?xml version="1.0" standalone="no"?>
<svg width="4cm" height="4cm" viewBox="0 0 400 400"
xmlns="http://www.w3.org/2000/svg" version="1.1">
<title>Example triangle01- simple example of a 'path'</title>
<desc>A path that draws a triangle</desc>
<rect x="1" y="1" width="398" height="398"
fill="none" stroke="blue" />
<path d="M 100 100 L 300 100 L 200 300 z"
fill="red" stroke="blue" stroke-width="3" />
</svg>
Example triangle01
Path data can contain newline characters and thus can be broken up into multiple lines to improve readability. Newlines inside attributes in markup will be normalized to space characters while parsing.
The syntax of path data is concise in order to allow for minimal file size and efficient downloads, since many SVG files will be dominated by their path data. Some of the ways that SVG attempts to minimize the size of path data are as follows:
The path data syntax is a prefix notation (i.e., commands followed by parameters). The only allowable decimal point is a Unicode U+0046 FULL STOP (".") character (also referred to in Unicode as PERIOD, dot and decimal point) and no other delimiter characters are allowed [UNICODE]. (For example, the following is an invalid numeric value in a path data stream: "13,000.56". Instead, say: "13000.56".)
For the relative versions of the commands, all coordinate values are relative to the current point at the start of the command.
Relative path commands are also influenced by the current bearing, which is an angle set by the bearing commands. This allows for paths to be specified using a style of "turtle graphics", where straight line and curved path segments are placed with their starting point at a tangent (or at some other angle) to the current bearing.
In the tables below, the following notation is used to describe the syntax of a given path command:
In the description of the path commands, cpx and cpy represent the coordinates of the current point, and cb represents the current bearing.
| Name: | d |
|---|---|
| Value: | none | <string> |
| Initial: | none |
| Applies to: | ‘path’ |
| Inherited: | no |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | as specified |
| Animatable: | yes |
The d property is used to specify the shape of a ‘path’ element.
The value none indicates that there is no path data for the element. For ‘path’ elements, this means that the element does not render or contribute to the bounding box of ancestor container elements.
A path is made up of multiple segments, and every command, either explicit or implicit, other than moveto or closepath, defines one path segment.
All coordinates and lengths specified within path data must be treated as being in user units in the current user coordinate system.
The <string> value specifies a shape using a path data string. The contents of the <string> value must match the svg-path EBNF grammar defined below, and errors within the string are handled according to the rules in the Path Data Error Handling section. If the path data string contains no valid commands, then the behavior is the same as the none value.
For animation, two d property values can only be interpolated smoothly when the path data strings contain have the same structure, (i.e. exactly the same number and types of path data commands which are in the same order). If an animation is specified and the lists of path data commands do not have the same structure, then the values must be interpolated using the discrete animation type.
If the list of path data commands have the same structure, then each parameter to each path data command must be interpolated separately as real numbers. Flags and booleans must be interpolated as fractions between zero and one, with any non-zero value considered to be a value of one/true.
Resolved that "d will become a presentation attribute (no name change) with path data string as value" at London Editor's Meeting.
The following sections list the commands that canbe used in path data strings. Those that draw straight line segments include the lineto commands (L, l, H, h, V and v) and the close path commands (Z and z). These three groups of commands draw curves:
The "moveto" commands (M or m) must establish a new initial point and a new current point. The effect is as if the "pen" were lifted and moved to a new location. A path data segment (if there is one) must begin with a "moveto" command. Subsequent "moveto" commands (i.e., when the "moveto" is not the first command) represent the start of a new subpath:
| Command | Name | Parameters | Description |
|---|---|---|---|
| M (absolute) m (relative) |
moveto | (x y)+ | Start a new sub-path at the given (x,y) coordinates. M (uppercase) indicates that absolute coordinates will follow; m (lowercase) indicates that relative coordinates will follow. If a moveto is followed by multiple pairs of coordinates, the subsequent pairs are treated as implicit lineto commands. Hence, implicit lineto commands will be relative if the moveto is relative, and absolute if the moveto is absolute. If a relative moveto (m) appears as the first element of the path, then it is treated as a pair of absolute coordinates. In this case, subsequent pairs of coordinates are treated as relative even though the initial moveto is interpreted as an absolute moveto. |
When a relative m command is used, the position moved to is (cpx + x cos cb + y sin cb, cpy + x sin cb + y cos cb).
The "closepath" (Z or z) must end the current subpath by connecting it back to its initial point in either of two ways:
complete, that is that all the required coordinate data has been supplied, then an automatic straight line must be drawn from the current point to the initial point of the current subpath. This path segment may be of zero length.
| Command | Name | Parameters | Description |
|---|---|---|---|
| Z or z |
closepath | (none) | Close the current subpath by connecting it back to the current subpath's initial point (see prose above). Since the Z and z commands take no parameters, they have an identical effect. |
SVG 2 adds the ability to fill in missing coordinate data with the Z or z command to avoid the need to add a zero length (or very short in the case of relative paths with rounding errors) path segment to close a subpath. This can effect the number of markers drawn and their orientation at the beginning/end of a closed subpath.
The use of Z or z to replace missing coordinate data with the coordinate of the initial point in a subpath was resolved at the Sydney (2015) meeting.
A closed subpath must be closed with a "closepath" command, this "joins" the first and last path segments. Any other path is an open subpath.
A closed subpath differs in behavior from an open subpath whose final coordinate is the initial point of the subpath. The first and last path segments of an open subpath will not be joined, even when the final coordinate of the last path segment is the initial point of the subpath. This will result in the first and last path segments being capped using the current value of stroke-linecap rather than joined using the current value of stroke-linejoin.
If a "closepath" is followed immediately by a "moveto", then the "moveto" identifies the start point of the next subpath. If a "closepath" is followed immediately by any other command, then the next subpath must start at the same initial point as the current subpath.
The current bearing does not affect a z command.
Examples:
The various "lineto" commands draw straight lines from the current point to a new point:
| Command | Name | Parameters | Description |
|---|---|---|---|
| L (absolute) l (relative) |
lineto | (x y)+ | Draw a line from the current point to the given (x,y) coordinate which becomes the new current point. L (uppercase) indicates that absolute coordinates will follow; l (lowercase) indicates that relative coordinates will follow. A number of coordinates pairs may be specified to draw a polyline. At the end of the command, the new current point is set to the final set of coordinates provided. |
| H (absolute) h (relative) |
horizontal lineto | x+ | Draws a horizontal line from the current point. H (uppercase) indicates that absolute coordinates will follow; h (lowercase) indicates that relative coordinates will follow. Multiple x values can be provided (although usually this doesn't make sense). An H or h command is equivalent to an L or l command with 0 specified for the y coordinate. At the end of the command, the new current point is taken from the final coordinate value. |
| V (absolute) v (relative) |
vertical lineto | y+ | Draws a vertical line from the current point. V (uppercase) indicates that absolute coordinates will follow; v (lowercase) indicates that relative coordinates will follow. Multiple y values can be provided (although usually this doesn't make sense). A V or v command is equivalent to an L or l command with 0 specified for the x coordinate. At the end of the command, the new current point is taken from the final coordinate value. |
When a relative l command is used, the end point of the line is (cpx + x cos cb + y sin cb, cpy + x sin cb + y cos cb).
When a relative h command is used, the end point of the line is (cpx + x cos cb, cpy + x sin cb). This means that an h command with a positive x value draws a line in the direction of the current bearing. When the current bearing is 0, this is a horizontal line in the direction of the positive x-axis.
When there is a non-zero bearing, a mnemonic for the h command could be "head this distance at the current bearing", rather than "draw a horizontal line".
When a relative v command is used, the end point of the line is (cpx + y sin cb, cpy + y cos cb).
The cubic Bézier commands are as follows:
| Command | Name | Parameters | Description |
|---|---|---|---|
| C (absolute) c (relative) |
curveto | (x1 y1 x2 y2 x y)+ | Draws a cubic Bézier 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. C (uppercase) indicates that absolute coordinates will follow; c (lowercase) indicates that relative coordinates will follow. Multiple sets of coordinates may be specified to draw a polybézier. At the end of the command, the new current point becomes the final (x,y) coordinate pair used in the polybézier. |
| S (absolute) s (relative) |
shorthand/smooth curveto | (x2 y2 x y)+ | Draws a cubic Bézier curve from the current point to (x,y). The first control point is assumed to be the reflection of the second control point on the previous command relative to the current point. (If there is no previous command or if the previous command was not an C, c, S or s, assume the first control point is coincident with the current point.) (x2,y2) is the second control point (i.e., the control point at the end of the curve). S (uppercase) indicates that absolute coordinates will follow; s (lowercase) indicates that relative coordinates will follow. Multiple sets of coordinates may be specified to draw a polybézier. At the end of the command, the new current point becomes the final (x,y) coordinate pair used in the polybézier. |
When a relative c or s command is used, each of the relative coordinate pairs is computed as for those in an m command. For example, the final control point of the curve of both commands is (cpx + x cos cb + y sin cb, cpy + x sin cb + y cos cb).
Example cubic01 shows some simple uses of cubic Bézier commands within a path. The example uses an internal CSS style sheet to assign styling properties. Note that the control point for the "S" command is computed automatically as the reflection of the control point for the previous "C" command relative to the start point of the "S" command.
<?xml version="1.0" standalone="no"?>
<svg width="5cm" height="4cm" viewBox="0 0 500 400"
xmlns="http://www.w3.org/2000/svg" version="1.1">
<title>Example cubic01- cubic Bézier commands in path data</title>
<desc>Picture showing a simple example of path data
using both a "C" and an "S" command,
along with annotations showing the control points
and end points</desc>
<style type="text/css"><![CDATA[
.Border { fill:none; stroke:blue; stroke-width:1 }
.Connect { fill:none; stroke:#888888; stroke-width:2 }
.SamplePath { fill:none; stroke:red; stroke-width:5 }
.EndPoint { fill:none; stroke:#888888; stroke-width:2 }
.CtlPoint { fill:#888888; stroke:none }
.AutoCtlPoint { fill:none; stroke:blue; stroke-width:4 }
.Label { font-size:22; font-family:Verdana }
]]></style>
<rect class="Border" x="1" y="1" width="498" height="398" />
<polyline class="Connect" points="100,200 100,100" />
<polyline class="Connect" points="250,100 250,200" />
<polyline class="Connect" points="250,200 250,300" />
<polyline class="Connect" points="400,300 400,200" />
<path class="SamplePath" d="M100,200 C100,100 250,100 250,200
S400,300 400,200" />
<circle class="EndPoint" cx="100" cy="200" r="10" />
<circle class="EndPoint" cx="250" cy="200" r="10" />
<circle class="EndPoint" cx="400" cy="200" r="10" />
<circle class="CtlPoint" cx="100" cy="100" r="10" />
<circle class="CtlPoint" cx="250" cy="100" r="10" />
<circle class="CtlPoint" cx="400" cy="300" r="10" />
<circle class="AutoCtlPoint" cx="250" cy="300" r="9" />
<text class="Label" x="25" y="70">M100,200 C100,100 250,100 250,200</text>
<text class="Label" x="325" y="350"
style="text-anchor:middle">S400,300 400,200</text>
</svg>
Example cubic01
The following picture shows some how cubic Bézier curves change their shape depending on the position of the control points. The first five examples illustrate a single cubic Bézier path segment. The example at the lower right shows a "C" command followed by an "S" command.
View
this example as SVG (SVG-enabled browsers only)
The quadratic Bézier commands are as follows:
| Command | Name | Parameters | Description |
|---|---|---|---|
| Q (absolute) q (relative) |
quadratic Bézier curveto | (x1 y1 x y)+ | Draws a quadratic Bézier curve from the current point to (x,y) using (x1,y1) as the control point. Q (uppercase) indicates that absolute coordinates will follow; q (lowercase) indicates that relative coordinates will follow. Multiple sets of coordinates may be specified to draw a polybézier. At the end of the command, the new current point becomes the final (x,y) coordinate pair used in the polybézier. |
| T (absolute) t (relative) |
Shorthand/smooth quadratic Bézier curveto | (x y)+ | Draws a quadratic Bézier curve from the current point to (x,y). The control point is assumed to be the reflection of the control point on the previous command relative to the current point. (If there is no previous command or if the previous command was not a Q, q, T or t, assume the control point is coincident with the current point.) T (uppercase) indicates that absolute coordinates will follow; t (lowercase) indicates that relative coordinates will follow. At the end of the command, the new current point becomes the final (x,y) coordinate pair used in the polybézier. |
When a relative q or t command is used, each of the relative coordinate pairs is computed as for those in an m command. For example, the final control point of the curve of both commands is (cpx + x cos cb + y sin cb, cpy + x sin cb + y cos cb).
Example quad01 shows some simple uses of quadratic Bézier commands within a path. Note that the control point for the "T" command is computed automatically as the reflection of the control point for the previous "Q" command relative to the start point of the "T" command.
<?xml version="1.0" standalone="no"?>
<svg width="12cm" height="6cm" viewBox="0 0 1200 600"
xmlns="http://www.w3.org/2000/svg" version="1.1">
<title>Example quad01 - quadratic Bézier commands in path data</title>
<desc>Picture showing a "Q" a "T" command,
along with annotations showing the control points
and end points</desc>
<rect x="1" y="1" width="1198" height="598"
fill="none" stroke="blue" stroke-width="1" />
<path d="M200,300 Q400,50 600,300 T1000,300"
fill="none" stroke="red" stroke-width="5" />
<!-- End points -->
<g fill="black" >
<circle cx="200" cy="300" r="10"/>
<circle cx="600" cy="300" r="10"/>
<circle cx="1000" cy="300" r="10"/>
</g>
<!-- Control points and lines from end points to control points -->
<g fill="#888888" >
<circle cx="400" cy="50" r="10"/>
<circle cx="800" cy="550" r="10"/>
</g>
<path d="M200,300 L400,50 L600,300
L800,550 L1000,300"
fill="none" stroke="#888888" stroke-width="2" />
</svg>
Example quad01
| SVG 2 Requirement: | Make it simpler to draw arcs in SVG path syntax. |
|---|---|
| Resolution: | Make arcs in paths easier. |
| Purpose: | To make it easier for authors to write path data with arcs by hand. |
| Owner: | Cameron (ACTION-3151) |
The elliptical arc commands are as follows:
| Command | Name | Parameters | Description |
|---|---|---|---|
| A (absolute) a (relative) |
elliptical arc | (rx ry x-axis-rotation large-arc-flag sweep-flag x y)+ | Draws an elliptical arc from the current point to (x, y). The size and orientation of the ellipse are defined by two radii (rx, ry) and an x-axis-rotation, which indicates how the ellipse as a whole is rotated, in degrees, relative to the current coordinate system. The center (cx, cy) of the ellipse is calculated automatically to satisfy the constraints imposed by the other parameters. large-arc-flag and sweep-flag contribute to the automatic calculations and help determine how the arc is drawn. |
When a relative a command is used, the end point of the arc is (cpx + x cos cb + y sin cb, cpy + x sin cb + y cos cb). The effective value of the x-axis-rotation parameter is also affected by the current bearing: it is computed as x-axis-rotation + cb.
Example arcs01 shows some simple uses of arc commands within a path.
<?xml version="1.0" standalone="no"?>
<svg width="12cm" height="5.25cm" viewBox="0 0 1200 400"
xmlns="http://www.w3.org/2000/svg" version="1.1">
<title>Example arcs01 - arc commands in path data</title>
<desc>Picture of a pie chart with two pie wedges and
a picture of a line with arc blips</desc>
<rect x="1" y="1" width="1198" height="398"
fill="none" stroke="blue" stroke-width="1" />
<path d="M300,200 h-150 a150,150 0 1,0 150,-150 z"
fill="red" stroke="blue" stroke-width="5" />
<path d="M275,175 v-150 a150,150 0 0,0 -150,150 z"
fill="yellow" stroke="blue" stroke-width="5" />
<path d="M600,350 l 50,-25
a25,25 -30 0,1 50,-25 l 50,-25
a25,50 -30 0,1 50,-25 l 50,-25
a25,75 -30 0,1 50,-25 l 50,-25
a25,100 -30 0,1 50,-25 l 50,-25"
fill="none" stroke="red" stroke-width="5" />
</svg>
Example arcs01
The elliptical arc command draws a section of an ellipse which must meet the following constraints:
For most situations, there are actually four different arcs (two different ellipses, each with two different arc sweeps) that satisfy these constraints. large-arc-flag and sweep-flag indicate which one of the four arcs are drawn, as follows:
The following illustrates the four combinations of large-arc-flag and sweep-flag and the four different arcs that will be drawn based on the values of these flags. For each case, the following path data command was used:
<path d="M 125,75 a100,50 0 ?,? 100,50"
style="fill:none; stroke:red; stroke-width:6"/>
where "?,?" is replaced by "0,0" "0,1" "1,0" and "1,1" to generate the four possible cases.
View this example as SVG (SVG-enabled browsers only)
Refer to Elliptical arc implementation notes for detailed implementation notes for the path data elliptical arc commands.
The bearing commands are at risk, with no known implementations.
The bearing commands (B or b) set the current bearing, which influences the orientation of subsequent relative path commands:
| Command | Name | Parameters | Description |
|---|---|---|---|
| B (absolute) b (relative) |
bearing | angle+ | Sets the current bearing. The parameter is an angle in degrees, where 0 indicates the direction of the positive x-axis. B (uppercase) sets the current bearing to the specified angle; b (lowercase) sets the current bearing to be the angle of the tangent at the end of the preceding path command plus the specified angle. The current point is unaffected. Although multiple parameters may be specified, this usually will not be useful, as they could be combined into a single angle value. |
At the beginning of a path, the current bearing is 0, which points in the direction of the positive x-axis. The current bearing remains unchanged until a B or b command is encountered. Since the relative b command sets the current bearing relative to the tangent at the end of the preceding path command, it is possible to set the bearing to that tangent by using "b 0".
The example below shows how bearing commands can be used to draw a regular pentagon.
<svg xmlns="http://www.w3.org/2000/svg"
width="300" height="100" viewBox="0 0 300 100">
<path fill="#eee"
stroke="deeppink" stroke-width="8px" stroke-linejoin="round"
d="M 150,10
B 36 h 47
b 72 h 47
b 72 h 47
b 72 h 47 z"/>
</svg>
Bearing commands can be used to position the end points of the sides of a regular polygon without having to use trigonometry to calculate them based on the polygon's interior angles.
SVG path data matches the following EBNF grammar.
svg_path::= wsp* moveto? (moveto drawto_command*)?
drawto_command::=
moveto
| closepath
| lineto
| horizontal_lineto
| vertical_lineto
| curveto
| smooth_curveto
| quadratic_bezier_curveto
| smooth_quadratic_bezier_curveto
| elliptical_arc
| bearing
moveto::=
( "M" | "m" ) wsp* coordinate_pair_sequence wsp* closepath?
closepath::=
("Z" | "z")
lineto::=
("L"|"l") wsp* (coordinate_pair_sequence | closepath)
horizontal_lineto::=
("H"|"h") wsp* coordinate_sequence
vertical_lineto::=
("V"|"v") wsp* coordinate_sequence
curveto::=
("C"|"c") wsp* (curveto_coordinate_sequence | (coordinate_pair_sequence? closepath))
curveto_coordinate_sequence::=
coordinate_pair_triplet
| (coordinate_pair_triplet comma_wsp? curveto_coordinate_sequence)
smooth_curveto::=
("S"|"s") wsp* (smooth_curveto_coordinate_sequence
| (coordinate_pair_sequence? closepath))
smooth_curveto_coordinate_sequence::=
coordinate_pair_double
| (coordinate_pair_double comma_wsp? smooth_curveto_coordinate_sequence)
quadratic_bezier_curveto::=
("Q"|"q") wsp*
(quadratic_bezier_curveto_coordinate_sequence | (coordinate_pair_sequence? closepath))
quadratic_bezier_curveto_coordinate_sequence::=
coordinate_pair_double
| (coordinate_pair_double comma_wsp? quadratic_bezier_curveto_coordinate_sequence)
smooth_quadratic_bezier_curveto::=
("T"|"t") wsp* (coordinate_pair_sequence | closepath)
elliptical_arc::=
( "A" | "a" ) wsp*
(elliptical_arc_argument_sequence
| (elliptical_arc_argument_sequence? elliptical_arc_closing_argument))
elliptical_arc_argument_sequence::=
elliptical_arc_argument
| (elliptical_arc_argument comma_wsp? elliptical_arc_argument_sequence)
elliptical_arc_argument::=
number comma_wsp? number comma_wsp? number comma_wsp
flag comma_wsp? flag comma_wsp? coordinate_pair
elliptical_arc_closing_argument::=
number comma_wsp? number comma_wsp? number comma_wsp
flag comma_wsp? flag comma_wsp? closepath
bearing::=
( "B" | "b" ) wsp* bearing_argument_sequence
bearing_argument_sequence::=
number | (number comma_wsp? bearing_argument_sequence)
coordinate_pair_double::=
coordinate_pair comma_wsp? coordinate_pair
coordinate_pair_triplet::=
coordinate_pair comma_wsp? coordinate_pair comma_wsp? coordinate_pair
coordinate_pair_sequence::=
coordinate_pair | (coordinate_pair comma_wsp? coordinate_pair_sequence)
coordinate_sequence::=
coordinate | (coordinate comma_wsp? coordinate_sequence)
coordinate_pair::= coordinate comma_wsp? coordinate
coordinate::= sign? number
sign::= "+"|"-"
number ::= ([0-9])+
flag::=("0"|"1")
comma_wsp::=(wsp+ ","? wsp*) | ("," wsp*)
wsp ::= (#x9 | #x20 | #xA | #xC | #xD)
The processing of the EBNF must consume as much of a given EBNF production as possible, stopping at the point when a character is encountered which no longer satisfies the production. Thus, in the string "M 100-200", the first coordinate for the "moveto" consumes the characters "100" and stops upon encountering the minus sign because the minus sign cannot follow a digit in the production of a "coordinate". The result is that the first coordinate will be "100" and the second coordinate will be "-200".
Similarly, for the string "M 0.6.5", the first coordinate of the "moveto" consumes the characters "0.6" and stops upon encountering the second decimal point because the production of a "coordinate" only allows one decimal point. The result is that the first coordinate will be "0.6" and the second coordinate will be ".5".
Note that the EBNF allows the path data string in the d property to be empty. This is not an error, instead it disables rendering of the path. Rendering is also disabled when the d property has the value none.
If path data not matching the grammar is encountered, then the path data is in error (see Error Handling).
Some features, such as the orientation of markers and the shapes of line caps, are defined in terms of the direction of the path at a given distance along the path or at the start or end of an individual segment.
The direction of a path at a specified distance along the path is defined as follows:
The direction at the start of a path segment is defined as follows:
The direction at the end of a path segment is defined as follows:
A conforming SVG user agent must implement path rendering as follows:
(newx1, newy1) = (curx - (oldx2 - curx), cury - (oldy2 - cury))
= (2*curx - oldx2, 2*cury - oldy2)
Various operations, including text on a path and motion animation and various stroke operations, require that the user agent compute the distance along the geometry of a graphics element, such as a ‘path’.
Exact mathematics exist for computing distance along a path, but the formulas are highly complex and require substantial computation. It is recommended that authoring products and user agents employ algorithms that produce as precise results as possible; however, to accommodate implementation differences and to help distance calculations produce results that approximate author intent, the ‘pathLength’ attribute can be used to provide the author's computation of the total length of the path so that the user agent can scale distance-along-a-path computations by the ratio of ‘pathLength’ to the user agent's own computed value for total path length.
A "moveto" or "bearing" operation within a ‘path’ element is defined to have zero length. Only the various "lineto", "curveto" and "arcto" commands contribute to path length calculations.
| Name | Value | Initial value | Animatable |
|---|---|---|---|
| pathLength | <number> | (none) | yes |
The author's computation of the total length of the path, in user units. This value is used to calibrate the user agent's own distance-along-a-path calculations with that of the author. The user agent will scale all distance-along-a-path computations by the ratio of ‘pathLength’ to the user agent's own computed value for total path length. ‘pathLength’ potentially affects calculations for text on a path, motion animation and various stroke operations.
A value of zero is valid and must be treated as a scaling factor of infinity. A value of zero scaled infinitely must remain zero, while any value greater than zero must become +Infinity.
A negative value is an error (see Error handling).
An SVGPathElement object represents a ‘path’ in the DOM.
interface SVGPathElement : SVGGeometryElement { };