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<!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN' 'http://www.w3.org/TR/html4/strict.dtd'>
<html lang="en">
<head profile="http://www.w3.org/2006/03/hcard">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>CSS Transforms</title>
<link rel="stylesheet" type="text/css" href="../default.css" />
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" />
<style type="text/css">
.term {
font-style: italic;
}
.todo {
font-weight: bold;
border-left: 0.5em solid #f44;
padding-left: 1em;
margin-top: 0.5em;
color: #a0a0a0;
}
.todo:before {
content: "TO DO : ";
color: #f44;
}
</style>
</head>
<body>
<div id="div-head" class="head">
<!--logo-->
<h1>CSS Transforms</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:
<dd>
<a href="[VERSION]">http://dev.w3.org/csswg/css3-transforms/</a>
<!--http://www.w3.org/TR/[YEAR]/WD-[SHORTNAME]-[CDATE]-->
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-transforms">[LATEST]</a>
<dt>Editor's draft:
<dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
<dt>Previous version:
<dd>None
<dt id="editors-list">Editors:
<dd>Simon Fraser (<a href="http://www.apple.com/">Apple Inc</a>) <simon.fraser @apple.com>
<dd>Dean Jackson (<a href="http://www.apple.com/">Apple Inc</a>) <dino @apple.com>
<dd>David Hyatt (<a href="http://www.apple.com/">Apple Inc</a>) <hyatt @apple.com>
<dd>Chris Marrin (<a href="http://www.apple.com/">Apple Inc</a>) <cmarrin @apple.com>
<dd>Edward O'Connor (<a href="http://www.apple.com/">Apple Inc</a>) <eoconnor @apple.com>
<dd>Dirk Schulze (<a href="http://www.adobe.com/">Adobe Systems, Inc</a>) <dschulze @adobe.com>
<dd>Aryeh Gregor (<a href="http://www.mozilla.org/">Mozilla</a>) <ayg @aryeh.name>
<dt>Issues list:
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transforms&resolution=---&cmdtype=doit">in Bugzilla</a>
<dt>Test suite:
<dd>none yet
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>CSS transforms allows elements styled with CSS to be transformed
in two-dimensional or three-dimensional space. This specification is the convergence of the
<a href="http://www.w3.org/TR/css3-2d-transforms/">CSS 2D transforms</a>,
<a href="http://www.w3.org/TR/css3-3d-transforms/">CSS 3D transforms</a>
and <a href="http://www.w3.org/TR/2009/WD-SVG-Transforms-20090320/">SVG transforms</a>
specifications.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<p class="note">
This specification merges the former CSS 2D Transforms and CSS 3D Transforms specifications and
will also merge CSS Transforms and SVG Transforms. The merge is in progress and the specification
is not yet ready for review.
</p>
<!--status-->
<p>
The <a href="ChangeLog">list of changes made to this specification</a> is
available.
</p>
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<h2>Introduction</h2>
<p><em>This section is not normative.</em></p>
<p>
The CSS <a href="http://www.w3.org/TR/REC-CSS2/visuren.html">visual
formatting model</a> describes a coordinate system within each
element is positioned. Positions and sizes in this coordinate space can
be thought of as being expressed in pixels, starting in the origin of point
with positive values proceeding to the right and down.
</p>
<p>
This coordinate space can be modified with the '<code
class="property">transform</code>' property. Using transform, elements
can be translated, rotated and scaled in two or three dimensional space.
</p>
<p>
Additional properties make working with transforms easier, and allow the
author to control how nested three-dimensional transforms interact.
</p>
<ul>
<li>
The '<code class="property">transform-origin</code>' property
provides a convenient way to control the origin about which transforms on
an element are applied.
</li>
<li>
The '<code class="property">perspective</code>' property allows the author
to make child elements with three-dimensional transforms appear as if they live in a common
three-dimensional space.
The '<code class="property">perspective-origin</code>' property provides control
over the origin at which perspective is applied, effectively changing the location of
the "vanishing point".
</li>
<li>
The '<code class="property">transform-style</code>' property allows 3D-transformed
elements and their 3D-transformed descendants to share a common three-dimensional
space, allowing the construction of hierarchies of three-dimensional objects.
</li>
<li>
The '<code class="property">backface-visibility</code>' property comes into play
when an element is flipped around via three-dimensional transforms such that its
reverse side is visible to the viewer. In some situations it is desirable to
hide the element in this situation, which is possible using the value of 'hidden'
for this property.
</li>
</ul>
<p>
Note that while some values of the '<code class="property">transform</code>' property
allow an element to be transformed in a three-dimensional coordinate system, the elements
themselves are not three-dimensional objects. Instead, they exist on a two-dimensional
plane (a flat surface) and have no depth.
</p>
<div class="issue">
There are two roles for transformations in layout: (1) transformations
that adjust the position of the affected content without changing the
normal layout of that content (much like relative positioning) and (2)
transformation of the content prior to layout that affects the layout
of that content. See <a
href="http://lists.w3.org/Archives/Public/www-style/2007Oct/0209">http://lists.w3.org/Archives/Public/www-style/2007Oct/0209</a>
for examples of both cases. The "transform" property (as defined in
this document) is equally useful for both roles. This document is
focused on satisfying the first role. There is, however, an
architectural question that arises because there needs to be a way to
distinguish which role an author of a stylesheet wants. The key
question is which is the default behavior/role for the "transform"
property and how is the other behavior/role indicated by a stylesheet
author. If you have an opinion on this topic, please send feedback.
</div>
<!-- ======================================================================================================= -->
<h2 id="module-interactions">Module Interactions</h2>
<p>Write me</p>
<h2 id="css-values">CSS Values</h2>
<p>Write me</p>
<h2 id="definitions">Definitions</h2>
<p> When used in this specification, terms have the meanings assigned in
this section.
</p>
<dl>
<dt id="TermBoundingBox"><dfn>bounding box</dfn></dt>
<dd>
<p>
A bounding box is the object bounding box for all SVG elements
without an associated CSS layout box and the border box for all
other elements. The bounding box of a table is the border box
of its
<a href="http://www.w3.org/TR/CSS21/tables.html#model">table wrapper box</a>,
not its table box.
</p>
</dd>
<dt id="TermTransformableElement"><dfn>transformable element</dfn></dt>
<dd>
<p>
A transformable element is an element in the HTML namespace
which is either a
<a href="http://www.w3.org/TR/CSS2/visuren.html#block-level">block-level</a>
or
<a href="http://www.w3.org/TR/CSS2/visuren.html#x13">atomic inline-level element</a>,
or whose '<code class="property">display</code>' property
computes to '<code class="css">table-row</code>',
'<code class="css">table-row-group</code>',
'<code class="css">table-header-group</code>',
'<code class="css">table-footer-group</code>',
'<code class="css">table-cell</code>', or
'<code class="css">table-caption</code>'; or an element in the
SVG namespace (see [[SVG11]]) which has the attributes
'<code class="property">transform</code>', 'patternTransform'
or 'gradientTransform'.
</p>
</dd>
<dt id="TermPerspectiveMatrix"><dfn>perspective matrix</dfn></dt>
<dd>
<p>
A matrix computed from the values of the '<code class="property">perspective</code>' and '<code class="property">perspective-origin</code>' properties as described <a href="#perspective-matrix-computation">below</a>.
</p>
</dd>
<dt id="TermTransformationMatrix"><dfn>transformation matrix</dfn></dt>
<dd>
<p>
A matrix computed from the values of the '<code class="property">transform</code>' and '<code class="property">transform-origin</code>' properties as described <a href="#transformation-matrix-computation">below</a>.
</p>
</dd>
<dt id="TermAccumulated3DTransformationMatrix">
<dfn>accumulated 3D transformation matrix</dfn>
</dt>
<dd>
<p>
A matrix computed for elements in a
<a href="#d-rendering-context">3D rendering context</a>, as
described
<a href="#accumulated-3d-transformation-matrix-computation">below</a>.
</p>
</dd>
<dt id="Term3DRenderingContext"><dfn>3D rendering context</dfn></dt>
<dd>
<p>
A containing block hierarchy of one or more levels, instantiated by elements with a computed value for
the '<code class="property">transform-style</code>' property of '<code class="css">preserve-3d</code>',
whose elements share a common three-dimensional coordinate system.
</p>
</dd>
<!-- Define "three-dimensional transform" ? -->
</dl>
<!-- ======================================================================================================= -->
<h2 id="transform-rendering">The Transform Rendering Model</h2>
<!-- This section is normative -->
<p>
Specifying a value other than '<code class="css">none</code>' for the '<code class="property">transform</code>'
property establishes a new <em>local coordinate system</em> at the element that it is
applied to. The mapping from where the element would have rendered into that local coordinate system
is given by the element's <a href="#TermTransformationMatrix"><i>transformation matrix</i></a>.
Transformations are cumulative. That is, elements establish their local
coordinate system within the coordinate system of their parent. From the perspective of the
user, an element effectively accumulates all the '<code class="property">transform</code>'
properties of its ancestors as well as any local transform applied to it. The accumulation
of these transforms defines a <em>current transformation matrix (CTM)</em> for the element.
</p>
<p>
The coordinate space behaves as described in the <a
href="http://www.w3.org/TR/SVG/coords.html#EstablishingANewUserSpace">coordinate
system transformations</a> section of the SVG 1.1 specification. This is
a coordinate system with two axes: the X axis increases horizontally to
the right; the Y axis increases vertically downwards. Three-dimensional
transform functions extent this coordinate space into three dimensions,
adding a Z axis perpendicular to the plane of the screen, that increases towards the viewer.
</p>
<p id="transformation-matrix-computation">
The <a href="#TermTransformationMatrix"><i>transformation matrix</i></a> is computed
from the '<code class="property">transform</code>' and '<code class="property">transform-origin</code>' properties
as follows:
<ol>
<li>Start with the identity matrix.</li>
<li>Translate by the computed X, Y and Z values of '<code class="property">transform-origin</code>'</li>
<li>Multiply by each of the transform functions in '<code class="property">transform</code>' property in turn</li>
<li>Translate by the negated computed X, Y and Z values of '<code class="property">transform-origin</code>'</li>
</ol>
</p>
<p>
Transforms apply to <span class="term">transformable elements</span>.
</p>
<div class="example">
<pre>
div {
transform: translate(100px, 100px);
}
</pre>
<p>This transform moves the element by 100 pixels in both the X and Y directions.</p>
<div class="figure">
<img src="transform1.png" alt="The 100px translation in X and Y">
</div>
</div>
<div class="example">
<pre>
div {
height: 100px; width: 100px;
transform: translate(80px, 80px) scale(1.5, 1.5) rotate(45deg);
}
</pre>
<p>This transform moves the element by 80 pixels in both the X and Y directions, then scales the element by 150%, then rotates it 45° clockwise about the Z axis. Note that the scale and rotation operate about the center of the element, since the element has the default transform-origin of '<code class="css">50% 50%</code>'.</p>
<div class="figure">
<img src="compound_transform.png" alt="The transform specified above">
</div>
<p>Note that an identical rendering can be obtained by nesting elements with the equivalent transforms:
<pre>
<div style="transform: translate(80px, 80px)">
<div style="transform: scale(1.5, 1.5)">
<div style="transform: rotate(45deg)"></div>
</div>
</div>
</pre>
</div>
<!-- This "in the HTML namespace" is awkward. Is there a better way? -->
<p>
In the HTML namespace, the transform property does not affect the flow of the content
surrounding the transformed element. However, the extent of the overflow
area takes into account transformed elements. This behavior is similar
to what happens when elements are offset via relative positioning.
Therefore, if the value of the '<code class="property">overflow</code>'
property is '<code class="css">scroll</code>' or '<code class="css">auto</code>',
scrollbars will appear as needed to see content that is transformed outside the visible area.
</p>
<p>
In the HTML namespace, any value other than '<code class="css">none</code>' for the transform results in the creation of
both a stacking context and a containing block. The object acts as a
containing block for fixed positioned descendants.
</p>
<p class="issue">
Is this effect on position:fixed necessary? If so, need to go into more detail here
about why fixed positioned objects should do this, i.e., that it's much harder to implement otherwise.
</p>
<p>
<a href="http://dev.w3.org/csswg/css3-background/#fixed0">Fixed backgrounds</a>
are affected by any transform specified for the root element,
and not by any other transforms.
</p>
<p class="note">
Thus an element with a fixed background still acts like a
"porthole" into an image that's fixed to the viewport, and
transforms on the element affect the porthole, not the
background behind it. On the other hand, transforming the root
element will still transform everything on the page, rather
than everything except for fixed backgrounds.
</p>
<p>
If the root element is transformed, the transformation applies
to the entire canvas, including any background specified for
the root element. Since
<a href="http://dev.w3.org/csswg/css3-background/#special-backgrounds">the
background painting area for the root element</a> is the entire
canvas, which is infinite, the transformation might cause parts
of the background that were originally off-screen to appear.
For example, if the root element's background were repeating
dots, and a transformation of
'<code class="css">scale(0.5)</code>' were specified on the
root element, the dots would shrink to half their size, but
there will be twice as many, so they still cover the whole
viewport.
</p>
<h3 id="transform-3d-rendering">3D Transform Rendering</h3>
<!-- Maybe define "tranform container" in the definitions, and use it everywhere
in place of "containing block"? I'm not sure if "containing block" is exactly right. -->
<p>
Normally, elements render as flat planes, and are rendered into the same plane
as their containing block. Often this is the plane shared by the rest of the page.
Two-dimensional transform functions can alter the appearance of an element, but
that element is still rendered into the same plane as its containing block.
</p>
<p>
Three-dimensional transforms can result in transformation matrices with a non-zero
Z component<!-- clarify -->, potentially lifting them off the plane of their
containing block. Because of this, elements with three-dimensional transformations
could potentially render in an front-to-back order that different from the normal CSS rendering order,
and intersect with each other. Whether they do so depends on whether the element is a member
of a <span class="term">3D rendering context</span>, as described below.
</p>
<div class="issue">
<p class="desc">This description does not exactly match what WebKit implements. Perhaps
it should be changed to match current implementations?</p>
</div>
<div class="example">
<p>This example shows the effect of three-dimensional transform applied to an element.
</p>
<pre>
<style>
div {
height: 150px;
width: 150px;
}
.container {
border: 1px solid black;
}
.transformed {
transform: rotateY(50deg);
}
</style>
<div class="container">
<div class="transformed"></div>
</div>
</pre>
<div class="figure">
<img src="examples/simple-3d-example.png" width="210" height="190" alt="Div with a rotateY transform.">
</div>
<p>The transform is a 50° rotation about the vertical, Y axis. Note how this makes the blue box appear
narrower, but not three-dimensional.
</p>
</div>
<p>
The '<code class="property">perspective</code>' and '<code class="property">perspective-origin</code>'
properties can be used to add a feeling of depth to a scene by making elements higher on the Z axis
(closer to the viewer) appear larger, and those further away to appear smaller.
</p>
<p id="perspective-matrix-computation">
The <a href="#TermPerspectiveMatrix"><i>perspective matrix</i></a> is computed as follows:
<!-- Make this more mathy, with matrices? -->
<ol>
<li>Start with the identity matrix.</li>
<li>Translate by the computed X and Y values of '<code class="property">perspective-origin</code>'</li>
<li>Multiply by the matrix that would be obtained from the '<a href="#perspective-function"><code class="css">perspective(<length>)</code></a>' transform function, where the length is provided by the value of the '<code class="property">perspective</code>' property</li>
<li>Translate by the negated computed X and Y values of '<code class="property">perspective-origin</code>'</li>
</ol>
</p>
<div class="example">
<p>This example shows how perspective can be used to cause three-dimensional transforms to appear more realistic.
</p>
<pre>
<style>
div {
height: 150px;
width: 150px;
}
.container {
perspective: 500px;
border: 1px solid black;
}
.transformed {
transform: rotateY(50deg);
}
</style>
<div class="container">
<div class="transformed"></div>
</div>
</pre>
<div class="figure">
<img src="examples/simple-perspective-example.png" width="210" height="190" alt="Div with a rotateY transform,
and perspective on its container">
</div>
<p>The inner element has the same transform as in the previous example, but its rendering is now influenced by the perspective
property on its parent element. Perspective causes vertices that have positive Z coordinates (closer to the viewer)
to be scaled up in X and Y, and those further away (negative Z coordinates) to be scaled down, giving an appearance of depth.
</p>
</div>
<p>
An element with a three-dimensional transform that is not contained in a
<span class="term">3D rendering context</span> renders with the appropriate
transform applied, but does not intersect with any other elements. The three-dimensional
transform in this case can be considered just as a painting effect, like two-dimensional
transforms. Similarly, the transform does not affect painting order. For example, a transform with a
positive Z translation may make an element look larger, but does not cause that element
to render in front of elements with no translation in Z.
</p>
<p>
An element with a three-dimensional transform that is contained in a
<span class="term">3D rendering context</span> can visibly interact with other elements
in that same 3D rendering context; the set of elements participating in the same
<span class="term">3D rendering context</span> may obscure each other or intersect,
based on their computed transforms. They are rendered as if they are all siblings,
positioned in a common 3D coordinate space. The position of each element in that three-dimensional
space is determined by accumulating the transformation matrices
up from the element that establishes the <span class="term">3D rendering context</span>
through each element that is a containing block for the given element, as described below.
<!-- More detail required, probably with matrices -->
</p>
<div class="example">
<pre>
<style>
div {
height: 150px;
width: 150px;
}
.container {
perspective: 500px;
border: 1px solid black;
}
.transformed {
transform: rotateY(50deg);
background-color: blue;
}
.child {
transform-origin: top left;
transform: rotateX(40deg);
background-color: lime;
}
</style>
<div class="container">
<div class="transformed">
<div class="child"></div>
</div>
</div>
</pre>
<p>This example shows how nested 3D transforms are rendered in the absence of '<code class="css">transform-style: preserve-3d</code>'. The blue div is transformed as in the previous example, with its rendering influenced by the perspective on its parent element. The lime element also has a 3D transform, which is a rotation about the X axis (anchored at the top, by virtue of the transform-origin). However, the lime element is being rendered into the plane of its parent because it is not a member of a 3D rendering context; the parent is "flattening".
</p>
<div class="figure">
<img src="examples/3d-rendering-context-flat.png" width="240" height="200" alt="Nested 3D transforms, with flattening">
</div>
</div>
<p>Elements establish and participate in 3D rendering contexts as follows:</p>
<ul>
<li>
A <span class="term">3D rendering context</span> is established by a
a <span class="term">transformable element</span> whose computed value for '<code class="property">transform-style</code>' is
'<code class="css">preserve-3d</code>', and which itself is not part of a 3D rendering context.
Note that such an element is always a containing block. An element that establishes a 3D rendering context
also participates in that context.
</li>
<li>
An element whose computed value for '<code class="property">transform-style</code>' is
'<code class="css">preserve-3d</code>', and which itself participates in a
<span class="term">3D rendering context</span>, extends that 3D rendering context rather than establishing
a new one.
</li>
<li>
An element participates in a <span class="term">3D rendering context</span> if its containing block
establishes or extends a <span class="term">3D rendering context</span>.
</li>
</ul>
<p id="accumulated-3d-transformation-matrix-computation">
The final value of the transform used to render an element in a <span class="term">3D rendering context</span>
is computed by accumulating an
<a href="#TermAccumulated3DTransformationMatrix">
accumulated 3D transformation matrix</a> as follows:
</p>
<ol>
<li>Start with the identity matrix.</li>
<li>For each containing block between the root of the <span class="term">3D rendering context</span>
and the element in question:
<ol>
<li>multiply the accumulated matrix with the <a href="#TermPerspectiveMatrix"><i>perspective matrix</i></a>
on the element's containing block (if any). That containing block is not necessarily a member
of the 3D rendering context.</li>
<li>apply to the accumulated matrix a translation equivalent to the horizontal and vertical offset of the element relative to
its containing block as specified by the CSS visual formatting model. <!-- (tighten this!) --></li>
<li>multiply the accumulated matrix with the <a href="#TermTransformationMatrix"><i>transformation matrix</i></a>.</li>
</ol>
</li>
</ol>
<div class="example">
<pre>
<style>
div {
height: 150px;
width: 150px;
}
.container {
perspective: 500px;
border: 1px solid black;
}
.transformed {
<b>transform-style: preserve-3d</b>;
transform: rotateY(50deg);
background-color: blue;
}
.child {
transform-origin: top left;
transform: rotateX(40deg);
background-color: lime;
}
</style>
</pre>
<p>This example is identical to the previous example, with the addition of '<code class="css">transform-style: preserve-3d</code>' on the blue element. The blue element now establishes a 3D rendering context, of which the lime element is a member. Now both blue and lime elements share a common three-dimensional space, so the lime element renders as tilting out from its parent, influenced by the perspective on the container.
</p>
<div class="figure">
<img src="examples/3d-rendering-context-3d.png" width="240" height="200" alt="Nested 3D transforms, with preserve-3d.">
</div>
</div>
<p>
Elements in the same <span class="term">3D rendering context</span> may intersect with each other. User agents must
render intersection by subdividing the planes of intersecting elements as described by
<a href="http://en.wikipedia.org/wiki/Newell's_algorithm">Newell's algorithm</a>.
</p>
<p>
Untransformed elements in a <span class="term">3D rendering context</span> render on the Z=0 plane, yet may still
intersect with transformed elements.
</p>
<p>
Within a <span class="term">3D rendering context</span>, the rendering order of non-intersecting elements is
based on their position on the Z axis after the application of the accumulated transform. Elements at the same
Z position render in <a href="http://www.w3.org/TR/CSS2/zindex.html#painting-order">stacking context order</a>.
</p>
<div class="example">
<pre>
<style>
.container {
background-color: rgba(0, 0, 0, 0.3);
transform-style: preserve-3d;
perspective: 500px;
}
.container > div {
position: absolute;
left: 0;
}
.container > :first-child {
transform: rotateY(45deg);
background-color: orange;
top: 10px;
height: 135px;
}
.container > :last-child {
transform: translateZ(40px);
background-color: rgba(0, 0, 255, 0.75);
top: 50px;
height: 100px;
}
</style>
<div class="container">
<div></div>
<div></div>
</div>
</pre>
<p>
This example shows show elements in a 3D rendering context can intersect. The container element establishes
a 3D rendering context for itself and its two children. The children intersect with eachother, and
the orange element also intersects with the container.
</p>
<div class="figure">
<img src="examples/3d-intersection.png" width="200" height="200" alt="Intersecting sibling elements.">
</div>
</div>
<p>
Using three-dimensional transforms, it's possible to transform an element such that its reverse side
is towards the viewer. 3D-tranformed elements show the same content on both sides, so the reverse side
looks like a mirror-image of the front side (as if the element were projected onto a sheet of glass).
Normally, elements whose reverse side is towards the viewer remain visible. However, the
'<code class="property">backface-visibility</code>' property allows the author to make an element invisible
when its reverse side is towards the viewer. This behavior is "live"; if an element with
'<code class="css">backface-visibility: hidden</code>' were animating,
such that its front and reverse sides were alternately visible, then it would only be visible when the
front side were towards the viewer.
</p>
<!-- ======================================================================================================= -->
<h2 id="transform-property">
The '<code class="property">transform</code>' Property
</h2>
<p>
A transformation is applied to the coordinate system an element
renders in through the '<code class="property">transform</code>' property. This property contains a
list of <a href="#transform-functions">transform functions</a>. The
final transformation value for a coordinate system is obtained by converting
each function in the list to its corresponding matrix like defined in <a href="#mathematical-description">Mathematical
Description of Transform Functions</a>, then multiplying the matrices.
</p>
<table class="propdef">
<tbody>
<tr>
<td>
<em>Name:</em>
</td>
<td>
<dfn id="effects">transform</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>
none | <transform-function> [ <transform-function> ]*
</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>
none
</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>
<a href="#TermTransformableElement">transformable elements</a>
</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>
no
</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>
refer to the size of the element's
<a href="#TermBoundingBox">bounding box</a>
</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>
visual
</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>
As specified, but with relative lengths converted into
absolute lengths.
</td>
</tr>
</tbody>
</table>
<p>Any value other than '<code class="css">none</code>' for the transform results in the creation of both a stacking context and a containing block. The object acts as a containing block for fixed positioned descendants.</p>
<!-- ======================================================================================================= -->
<h2 id="svg-transform">
The SVG '<code class="property">transform</code>' Attribute
</h2>
<p>
The <a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/">SVG 1.1 specification</a> did not
specify the attributes '<code class="property">transform</code>', 'gradientTransform' or 'patternTransform' as
<a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/styling.html#UsingPresentationAttributes"><em>presentation attributes</em></a>.
In order to improve the integration of SVG and HTML, this specification makes these SVG attributes
'presentation attributes' and makes the '<code class="property">transform</code>' property one that applies to <span class="term">transformable elements</span> in the SVG namespace.
</p>
<p>
This specification will also introduce the new presentation attributes '<code class="property">transform-origin</code>',
'<code class="property">perspective</code>', '<code class="property">perspective-origin</code>',
'<code class="property">transform-style</code>' and '<code class="property">backface-visibility</code>'.
All new introduced presentation attributes are animatable.
</p>
<h3 id="transform-attribute-specificity">SVG '<code class="property">transform</code>' attribute specificity</h3>
<p>Since the previously named SVG attributes become presentation attributes, their participation in the CSS
cascade is determined by the specificity of presentation attributes, as
<a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/styling.html#UsingPresentationAttributes">explained</a>
in the SVG specification.
</p>
<div class="example">
<p>
This example shows the combination of the '<code class="property">transform</code>' style property and the '<code class="property">transform</code>' presentation attribute.
</p>
<pre><svg xmlns="http://www.w3.org/2000/svg">
<style>
.container {
transform: translate(100px, 100px);
}
</style>
<g class="container" transform="translate(200 200)">
<rect width="100" height="100" fill="blue" />
</g>
</svg></pre>
<div class="figure">
<img src="examples/svg-translate.png" width="200" height="200" alt="Translated SVG container element.">
</div>
<p>
Because of the participation to the CSS cascade, the '<code class="property">transform</code>' style property overrides the
'<code class="property">transform</code>' presentation attribute. Therefore the container gets translated by '<code class="css">100px</code>' in both the horizontal and
the vertical directions, instead of '<code class="css">200px</code>'.
</p>
</div>
<h3 id="svg-syntax">Syntax of the SVG 'transform' attribute</h3>
<p>
To provide backwards compatibility, the syntax of the '<code class="property">transform</code>' presentation attribute differs from
the syntax of the '<code class="property">transform</code>' style property as shown in the example above. However, the syntax
used for the '<code class="property">transform</code>' style property can be used for a '<code class="property">transform</code>' presentation attribute value.
Authors are advised to follow the rules of <a href="http://www.w3.org/TR/css3-values/#functional-notation">CSS Values and Units Module</a>.
Therefore an author should write '<code class="css">transform="translate(200px, 200px)"</code>' instead of
'<code class="css">transform="translate (200 200)"</code>' because the second example with the spaces before the '<code class="css">(</code>',
the missing comma between the arguments and the values without the explicit unit notation would be valid for
the attribute only.
</p>
<h4 id="svg-transform-list">Transform List</h4>
<p>
The value for the 'transform' attribute consists of a transform list with zero or more transform functions
using <a href="#svg-functional-notation">functional notation</a>. If the transform list consists of more than one transform function,
these functions are separated by optional whitespace, an optional comma (‘<code class="css">,</code>’) and optional whitespace.
The transform list can have optional whitespace characters before and after the list.
</p>
<h4 id="svg-functional-notation">Functional Notation</h4>
<p>
The syntax starts with the name of the function followed by optional whitespace characters followed by a left
parenthesis followed by optional whitespace followed by the argument(s) to the notation followed by
optional whitespace followed by a right parenthesis. If a function takes more than one argument, the
arguments are either separated by a comma (‘<code class="css">,</code>’) with optional whitespace characters before and after the comma,
or by one or more whitespace characters.
</p>
<h4 id="svg-data-types">SVG Data Types</h4>
<p>
Arguments of transform functions consist of data types in the sense of
<a href="http://www.w3.org/TR/css3-values/#functional-notation">CSS Values and Units Module</a>. The definitions of
data types in CSS Values and Units Module are enhanced as follows:
</p>
<h5 id="svg-transform-value">The <var><translation-value></var> and <var><length></var> type</h5>
<p>
A translation-value or length can be a <var><number></var> without an unit identifier. In this case
the <a href="#svg-number"><var>number</var></a> gets interpreted as "user unit". A user unit in the the
<a href="http://www.w3.org/TR/2003/REC-SVG11-20030114/coords.html#InitialCoordinateSystem">initial
coordinate system</a> is equivalent to the parent environment's notion of a pixel unit.
</p>
<h5 id="svg-angle">The <var><angle></var> type</h5>
<p>
An angle can be a <var><number></var> without an unit identifier. In this case the <a href="#svg-number"><i>number</i></a>
gets interpreted as a value in degrees.
</p>
<h5 id="svg-number">The <var><number></var> type</h5>
<p>
SVG supports scientific notations for numbers. Therefore a <var>number</var> gets parsed like described in SVG
<a href="http://www.w3.org/TR/SVG/types.html#DataTypeNumber">Basic data types</a> for SVG attributes.
</p>
<h3 id="svg-gradient-transform-pattern-transform">The SVG 'gradientTransform' and 'patternTransform' attributes</h3>
<p>
SVG specifies the attributes 'gradientTransform' and 'patternTransform'. This specification
makes both attributes presentation attributes. Both attributes use the same <a href="#svg-syntax">syntax</a> as
the SVG '<code class="property">transform</code>' attribute. This specification does not introduce corresponding CSS style properties. Both, the 'gradientTransform' and the 'patternTransform' attribute, are presentation attributes for the 'transform' property.
</p>
<h3 id="svg-transform-functions">SVG transform functions</h3>
<p>
For backwards compatibility with existing SVG content, this specification supports all transform functions
defined by <a href="http://www.w3.org/TR/SVG/coords.html#TransformAttribute">The '<code class="property">transform</code>' attribute</a> in SVG 1.1.
Therefore the two-dimensional transform function '<code class="css">rotate(<angle>)</code>' is extended as follows:
</p>
<dl>
<dt>
<code class="css">rotate(<angle>[, <translation-value>, <translation-value>])</code>
</dt>
<dd>
specifies a <a href="#RotateDefined">2D rotation</a> by the angle specified in the parameter about the origin of the element, as defined
by the '<code class="property">transform-origin</code>' property. If the optional translation values are specified, the transform origin is translated by that amount
(using the current transformation matrix) for the duration of the rotate operation.
For example '<code class="css">rotate(90deg, 100px, 100px)</code>' would elements cause to appear rotated one-quarter of a turn in the clockwise direction after a translation
of 100 pixel in the vertical and horizontal direction.
</dd>
</dl>
<p>
User agents are just required to support the two optional arguments for translation on elements in the SVG namespace.
</p>
<h3 id="svg-three-dimensional-functions">SVG and 3D transform functions</h3>
<p>
This specification explicitly requires
three-dimensional transform functions to apply to the
<a href="http://www.w3.org/TR/SVG/intro.html#TermContainerElement"><em>container elements</em></a>:
'a', 'g', 'svg', all <a href="http://www.w3.org/TR/SVG/intro.html#TermGraphicsElement"><em>graphics elements</em></a>, all
<a href="http://www.w3.org/TR/SVG/intro.html#TermGraphicsReferencingElement"><em>graphics referencing elements</em></a>
and the SVG <a href="http://www.w3.org/TR/SVG/extend.html#ForeignObjectElement">'foreignObject'</a> element.
</p>
<p>
Three-dimensional transform functions and the properties '<code class="property">perspective</code>',
'<code class="property">perspective-origin</code>', '<code class="property">transform-style</code>'
and '<code class="property">backface-visibility</code>' can not be used for the elements: 'clipPath', 'mask', 'linearGradient',
'radialGradient' and 'pattern'. If a transform list includes a three-dimensional transform function, the complete
transform list must be ignored. The values of every previously named property must be ignored.
<span class="term">Transformable elements</span> that are contained by one of these elements can have three-dimensional transform functions.
Before a 'clipPath', 'mask' or 'pattern' element can get applied to a target element, user agents must take the drawn results as static
images in analogue of "flattening" the elements and taking the rendered content as a two-dimensional canvas.
</p>
<h3 id="svg-object-bounding-box">Object bounding box units</h3>
<p>
Percentage or fractional values in SVG are either relative to the elements viewport units or to the element's
<a href="http://www.w3.org/TR/SVG/coords.html#ObjectBoundingBoxUnits">object bounding box units</a> as
specified in SVG 1.1. To align with HTML, all percentage values for all properties defined in this specification
are relative to the object bounding box units.
</p>
<p>
If an SVG element does not provide a bounding box (like for the 'pattern', 'mask' or 'clipPath' elements), the bounding box
is treated as if the position x, y and the dimensions width and height are zero. Percentage values or keywords won't affect the
rendering and are treated as if zero was specified.
</p>
<div class="example">
<p>
The '<code class="property">transform-origin</code>' property on the pattern in the following example specifies a '<code class="css">50%</code>' translation of the origin in the horizontal and vertical dimension.
The '<code class="property">transform</code>' property specifies a translation as well, but in absolute lengths.
</p>
<pre><svg xmlns="http://www.w3.org/2000/svg">
<style>
pattern {
transform: translate(50px, 50px) rotate(45deg);
transform-origin: 50% 50%;
}
</style>
<defs>
<pattern id="pattern-1">
<rect id="rect1" width="100" height="100" fill="blue" />
</pattern>
</defs>
<rect width="100" height="100" fill="url(#pattern-1)" />
</svg></pre>
<p>
An SVG 'pattern' element doesn't have a bounding box. Therefore the relative values of the
'<code class="property">transform-origin</code>' property don't affect the rendering and are treated
as if zero was specified. The translation on the '<code class="property">transform</code>' property is in
absolute coordinates and translate the coordinate system by 50 pixels in each direction.
</p>
</div>
<h3 id="transform-attribute-dom">SVG DOM interface for the '<code class="property">transform</code>' attribute</h3>
<p>
The SVG specification defines the
'<a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/coords.html#InterfaceSVGAnimatedTransformList"><code class="property">SVGAnimatedTransformList</code></a>'
interface in the SVG DOM to provide access to the animated and the base value of the SVG 'transform', 'gradientTransform' and 'patternTransform' attributes. To ensure backwards compatibility,
this API must still be supported by user agents.
</p>
<p>
The '<code class="property">transform</code>' property contributes to the CSS cascade. According to SVG 1.1 user agents conceptually insert a
<a href="http://www.w3.org/TR/SVG/styling.html#UsingPresentationAttributes">new author
style sheet</a> for presentation attributes, which is the first in the author style sheet collection.
'<code class="property">baseVal</code>' gives the author the possibility to access and modify the values of the SVG '<code class="property">transform</code>' attribute.
To provide the necessary backwards compatibility to the SVG DOM, '<code class="property">baseVal</code>' must reflect the values of this author style sheet.
All modifications to SVG DOM objects of '<code class="property">baseVal</code>' must affect this author style sheet immediately.
</p>
<p>
'<code class="property">animVal</code>' represents the computed style of the '<code class="property">transform</code>' property. Therefore it includes all applied
<a href="http://www.w3.org/TR/css3-transitions/">CSS3 Transitions</a>, <a href="http://www.w3.org/TR/css3-animations/">CSS3
Animations</a> or <a href="#svg-animation">SVG Animations</a> if any of those are underway. The computed style and SVG DOM
objects of '<code class="property">animVal</code>' can not be modified.
</p>
<p>