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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">
.prop-name {
font-weight: bold;
}
.prop-value {
font-family: monospace;
}
.term {
font-style: italic;
}
div.issue-marker {
position: absolute;
width: 20ex;
margin-left: -26ex;
padding-right: 0.5em;
font-weight: normal;
font-size: 11px;
text-align: right;
background-color: white;
font-size: 90%;
padding-top: 0px;
padding-bottom: 0px;
}
div.issue-marker a {
color: red;
}
div.issue-marker .desc {
font-size: 80%;
line-height: 1.4em;
}
div.issue-marker .desc strong {
font-weight: bold;
font-size: 120%;
color: red;
}
.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>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>Vincent Hardy (<a href="http://www.adobe.com/">Adobe Systems, Inc</a>) <vhardy @adobe.com>
<dd>Dirk Schulze (<a href="http://www.adobe.com/">Adobe Systems, Inc</a>) <dschulze @adobe.com>
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<strong>THIS IS A WORK IN PROGRESS AND NOT READY FOR REVIEW.</strong>
<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>
<!--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 which each
element is positioned. Positions and sizes in this coordinate space can
be thought of as being expressed in pixels, starting in the upper left
corner of the parent with positive values proceeding to the right and
down.
</p>
<p>
This coordinate space can be modified with the <span
class="prop-name">'transform'</span> 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 <span class="prop-name">'transform-origin'</span> property
provides a convenient way to control the origin about which transforms on
an element are applied.
</li>
<li>
The <span class="prop-name">'perspective'</span> property allows the author
to make child elements with three-dimensional transforms appear as if they live in a common
three-dimensional space.
The <span class="prop-name">'perspective-origin'</span> property provides control
over the origin at which perspective is applied, effectively changing the location of
the "vanishing point".
</li>
<li>
The <span class="prop-name">'transform-style'</span> 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 <span class="prop-name">'backface-visibility'</span> 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 <span class="prop-name">'transform'</span> 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>
<div class="issue">
What do fixed backgrounds do in transforms? They should probably ignore
the transform completely, since - even transformed - the object should
be acting as "porthole" through which the fixed background can be viewed
in its original form.
</div>
<!-- ======================================================================================================= -->
<h2 id="module-interactions">Module Interactions</h2>
<p>Write me</p>
<h2 id="module-interactions">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="TermTransformableElement">
<span class="termDefine">transformable element</span>
</dt>
<dd>
<p>
A transformable element in the HTML namespace which is either be a block-level or atomic inline-level
element, or an element the SVG namespace (see [[SVG11]]) which has the attributes 'transform',
'patternTransform' or 'gradientTransform'.
</p>
</dd>
<dt id="Term3DRenderingContext">
<span class="termDefine">3D rendering context</span>
</dt>
<dd>
<p>
All elements in the same <span class="term">3D rendering context</span> share a common three-dimensional
coordinate system. Elements in the same 3D rendering context which intersect
may be rendered as intersecting by the user agent.
</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 'none' for the <span class="prop-name">'transform'</span>
property establishes a new <em>local coordinate system</em> at the element that it is
applied to. 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 <span class="prop-name">'transform'</span>
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>
Transforms apply to <a href="#TermTransformableElement">transformable elements</a>.
</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>Move the element by 80 pixels in both the X and Y directions, then scale the element by 150%, then rotate it 45 degrees clockwise about the Z axis. Note that the scale and rotate operate about the center of the element, since the element has the default transform-origin of 50% 50%.</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 value of the overflow
area takes into account transformed elements. This behavior is similar
to what happens when elements are translated via relative positioning.
Therefore, if the value of the <span class="prop-name">'overflow'</span>
property is <span class="prop-value">'scroll'</span> or <span
class="prop-value">'auto'</span>, 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 'none' 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 affect 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>
<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 the 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> or not, as described below.
</p>
<div class="issue issue-marker">
<p class="desc">This description does not exactly match what WebKit implements. Perhaps
it should be changed to match current implementations?</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>
<div class="example">
<p>This example shows the effect of three-dimensional transform applied to an element.
</p>
<pre>
div { height: 150px; width: 150px; }
.container { border: 1px solid black; }
.transformed { transform: rotateY(50deg); }
</pre>
<pre>
<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>
<div class="example">
<p>This example shows how perspective can be used to cause three-dimensional transforms to appear more realistic.
</p>
<pre>
div { height: 150px; width: 150px; }
.container { perspective: 500px; border: 1px solid black; }
.transformed { transform: rotateY(50deg); }
</pre>
<pre>
<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 Example 1, 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 futher 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 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>
<p>
A <span class="term">3D rendering context</span> is established via the following:
</p>
<ul>
<li>
A transformable element has a value for the <span type="prop-name">perspective</span> property
which is not 'none' and greater than 0, and which is not itself part of a 3D rendering context.
</li>
<!-- Part of is wooly. Need to clarify. -->
<li>
An transformable element whose computed value of <span type="prop-name">transform-style</span> is
<span class="prop-value">'perserve-3d'</span>, and which itself is not part of a 3D rendering context.
</li>
</ul>
<div class="issue issue-marker">
<p class="desc">Should intersection behavior be normative?</p>
</div>
<p>
An element whose computed value for <span type="prop-name">transform-style</span> is
<span style="prop-value">'preserve-3d'</span>, and which is itself a member of a
<span class="term">3D rendering context</span>, extends the 3D rendering context of which it is a member
to the elements for which it acts as a containing block.
</p>
<p>
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>.
</p>
<!-- Need more exposition here on establishes vs. participates -->
<p>
The final value of the transform used to render an element in a <span class="term">3D rendering context</span>
is computed as follows:
</p>
<ol>
<!-- Clarify pre- vs post-multiply? -->
<li>Start with the identity matrix</li>
<li>If the root of the <span class="term">3D rendering context</span> has perspective, multiply that into
the matrix, taking perspective-origin into account.</li>
<li>For each ancestor of the element in question, compute a transformation matrix by:
<ol>
<li>applying perpsective and perspective-origin, if any</li>
<li>applying a translation equivalent to the horizontal and vertical offset of the element relative to
its containing block as specified by CSS layout rules <!-- (tighten this!) --></li>
<li>applying transform and transform-origin, if any</li>
</ol>
The target matrix is then multiplied with the matrix for this ancestor.
</li>
</ol>
<!-- Discuss whether an element that establishes a 3D rendering context also participates in it; notably,
does the foreground/background of the element intersect with transformed members of the 3D rendering context? -->
<!-- Discuss whether non-transformed memebers of the <span class="term">3D rendering context</span> participate in intersection -->
<div class="issue issue-marker">
<p class="desc">Does transform-style follow containing block, or parent element ancestry?</p>
</div>
<div class="issue issue-marker">
<p class="desc">Does perspective establish a 3D rendering context?</p>
</div>
<div class="example">
<pre>
</pre>
<p>Example of simple 3D rendering context
</p>
<div class="figure">
</div>
</div>
<div class="example">
<pre>
</pre>
<p>Example of deeper 3D rendering context
</p>
<div class="figure">
</div>
</div>
<div class="example">
<pre>
</pre>
<p>Example of flattening inside 3D rendering context
</p>
<div class="figure">
</div>
</div>
<!--
<p>
The <span class="prop-name">'transform-style'</span> property defines
how nested elements are rendered in three-dimensional space. If the <span
class="prop-name">'transform-style'</span> is <span
class="prop-value">'flat'</span>, all children of this element are
rendered flattened into the 2D plane of the element. Therefore, rotating
the element about the X or Y axes will cause children positioned at
positive or negative Z positions to appear on the element's plane, rather
than in front of or behind it. If the <span
class="prop-name">'transform-style'</span> is <span
class="prop-value">'preserve-3d'</span>, this flattening is not performed,
so children maintain their position in three-dimensional space.
</p>
<p>
This flattening takes place at each element, so preserving a hierarchy
of elements in three-dimensional space requires that each element in the hierarchy
have the value <span class="prop-value">'preserve-3d'</span> for <span
class="prop-name">'transform-style'</span>. But since <span
class="prop-name">'transform-style'</span> affects only an element's
children, the leaf nodes in a hierarchy do not require the
<span class="prop-name">'transform-style: preserve-3d'</span> to be specified.
</p>
<p>
For some effects, the author will have to ensure that an ancestor
element to a subtree using <span class="prop-value">'preserve-3d'</span>
has a <span class="prop-name">'transform-style'</span> of <span
class="prop-value">'flat'</span> (or the default). Otherwise, the
elements in the 3D tree may be located behind ancestor elements and,
thus, invisible (hidden behind an ancestor's background).
</p>
<p>
Note that while 'preserve-3d' can be specified on an element, the effect may not
be possible. Elements that have <span class="prop-name">'overflow'</span> set to
<span class="prop-value">'hidden'</span> are unable to keep their children in 3D.
In this case the element will behave as if the property was set to
<span class="prop-value">'flat'</span>.
</p>
-->
<!-- ======================================================================================================= -->
<h2 id="transform-property">
The <span class="prop-name">'transform'</span> Property
</h2>
<p>
A transformation is applied to the coordinate system an element
renders in through the <span class="prop-name">'transform'</span> 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 (either defined in
this specification or by reference to the SVG specification), 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 border box
</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>
visual
</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>
See below.
</td>
</tr>
</tbody>
</table>
<div class="issue issue-marker">
<p class="desc">We need to resolve whether the computed value is the same as the specified value, or matrix().</p>
</div>
<p>The computed value of the transform property is a matrix() or matrix3d() value that describes the matrix that results from concatenating the individual transform functions. If the resulting matrix can be represented as a two-dimensional matrix with no loss of information, then a matrix() value is returned, otherwise a matrix3d() value. For elements with no transform applied, the computed value is 'none'.</p>
<!-- ======================================================================================================= -->
<h3 id="svg-transform">The SVG transform attribute</h3>
<p>The <a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/">SVG 1.1 specification</a> did not
specify the 'transform' attribute as a <a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/styling.html#UsingPresentationAttributes">presentation attribute</a>.
In order to improve the integration of
SVG and HTML, this specification makes the SVG 'transform' attribute a
'presentation attribute' and makes the 'transform' property one that applies to SVG elements.</p>
<h4 id="transform-attribute-specificity">SVG transform attribute specificity</h4>
<p>Since the SVG attribute becomes a presentation attribute, its participation to 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>
<h4 id="transform-attribute-dom">SVG transform attribute DOM</h4>
<p>The SVG specification <a href="http://www.w3.org/TR/2011/REC-SVG11-20110816/coords.html#InterfaceSVGAnimatedTransformList">defines</a> a DOM interface to access the animated and base value of
the SVG transform attribute. To ensure backwards compatibility, this API should still be
supported by user agents. The <code>baseVal</code> should be the value of the 'transform' attribute,
as set on the element, and the <code>animVal</code> should be the property's computed value which account
for CSS animation, if any is underway.</p>
<div class="issue">
<ul>
<li>Should we also make gradientTransform and patternTransform presentation attributes?
Proposal: they
are the 'presentation attributes' for <gradient> and >pattern< respectively,
for the 'transform' property (i.e., there is no 'gradientTransform' property. Instead, the
'gradientTransform' is a presentation attribute that provides a value for the
'transform' property that applies to the <gradient> element.)</li>
<li>Is this proposal working for SMIL animation of the transform property?</li>
</ul>
</div>
<!-- ======================================================================================================= -->
<h2 id="transform-origin-property">
The <span class="prop-name">'transform-origin'</span> Property
</h2>
<div class="issue issue-marker">
<p class="desc">Need to add 3D transform-origin variant in a way that is not ambiguous
with the background-origin syntax (<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15432">bug 15432</a>).</p>
</div>
<p>
The <span class="prop-name">'transform-origin'</span> property
establishes the origin of transformation for a coordinate system. This property
is applied by first translating the element's coordinate system by the negated value of the
property, then applying the local transform, then translating by the
property value. This effectively moves the desired transformation origin
of the element to (0,0) in the local coordinate system, then applies
the local transform, then moves the element back to its original
position.
</p>
<p>If only one value is specified, the second value is assumed to be
'center'. If two values are given and at least one value is not a keyword,
then the first value represents the horizontal position (or offset) and
the second represents the vertical position (or
offset). <var><percentage></var> and <var><length></var>
values here represent an offset of the transform origin from the top left corner
of the element's border box.
</p>
<p>If three or four values are given, then
each <var><percentage></var> or<var><length></var>
represents an offset and must be preceded by a keyword,
which specifies from which edge the offset is given. For example,
''transform-origin: bottom 10px right 20px'' represents a
''10px'' vertical offset up from the bottom edge and a
''20px'' horizontal offset leftward from the right edge. If
three values are given, the missing offset is assumed to be zero.
</p>
<p>Positive values represent an offset <em>inward</em> from the edge of
the border box. Negative values represent an offset
<em>outward</em> from the edge of the border box.
</p>
<table class="propdef">
<tbody>
<tr>
<td>
<em>Name:</em>
</td>
<td>
<dfn id="transform-origin">transform-origin</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>
[ top | bottom ] |<br>
[ <percentage> | <length> | left | center | right ] [ <percentage> | <length> | top | center | bottom ]? |<br>
[ center | [ left | right ] [ <percentage> | <length> ]? ] && [ center | [ top | bottom ] [ <percentage> | <length> ]? ]<br>
</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>
0 0 for SVG elements, 50% 50% for all other elements
</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>
<a href="#TermTransformableElement">transformable element</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 border box
</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>
visual
</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>
For <length> the absolute value, otherwise a percentage
</td>
</tr>
</tbody>
</table>
<h3 id="svg-transform-origin">The 'transform-origin' property for SVG elements</h3>
<div class="issue issue-marker">
<p class="desc">Should we use 'auto', or explicitly say that transform-origin is 0 0 for SVG elements, 50% 50% for all other elements (<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15504">bug 15504</a>)?</p>
</div>
<p>To keep the 'transform' property compatible with existing SVG content that assumed a top/left
coordinate system origin, the user agent stylesheet must contain the following:</p>
<pre class="css">
svg | * {
transform-origin: top left;
}
</pre>
<div class="issue">
<p class="desc">Need to determine how to extend transform-origin to allow it ot affect the z-origin
with three-dimensional transforms (<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=14647">Bug 14647</a>).
</div
<!-- ======================================================================================================= -->
<h2 id="transform-style-property">
The <span class="prop-name">'transform-style'</span> Property
</h2>
<p>
Property summary here.
</p>
<table class="propdef">
<tbody>
<tr>
<td>
<em>Name:</em>
</td>
<td>
<dfn id="transform-style">transform-style</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>
flat | preserve-3d
</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>
flat
</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>
N/A
</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>
visual
</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>
Same as specified value.
</td>
</tr>
</tbody>
</table>
<p>
A value of <span class="prop-value">preserve-3d</span> for <span class="prop-name">transform-style</span>
establishes a stacking context.
</p>
<div class="issue issue-marker">
<p class="desc">Should this affect the computed value of transform-style?</p>
</div>
<p>
The following CSS property values require the user agent to create a flattened representation of
the descendant elements before they can be applied, and therefore override the behavior of
<span class="prop-name">transform-style</span>: <span class="prop-value">preserve-3d</span>:
<ul>
<li><span class="prop-name">overflow</span>: any value other than 'visible'.</li>
<li><span class="prop-name">opacity</span>: any value other than 1.</li>
<li><span class="prop-name">filter</span>: any value other than 'none'.</li>
<!-- Others? -->
</ul>
</p>
<!-- ======================================================================================================= -->
<h2 id="perspective-property">
The <span class="prop-name">'perspective'</span> Property
</h2>
<p>
<p>
The <span class="prop-name">'perspective'</span> property applies the
same transform as the <span
class="prop-value">perspective(<length>)</span> transform
function, except that it applies only to the positioned or transformed
children of the element, not to the transform on the element itself.
</p>
<table class="propdef">
<tbody>
<tr>
<td>
<em>Name:</em>
</td>
<td>
<dfn id="perspective">perspective</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>
none | <length>
</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>
N/A
</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>
visual
</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>
Same as specified value.
</td>
</tr>
</tbody>
</table>
<p>
If the value is <span
class="prop-value">'none'</span>, less than or equal to 0 no perspective transform is applied.
</p>
<p>
The use of this property with any value other than 'none' establishes a
stacking context. It also establishes a containing block (somewhat
similar to position:relative), just like the 'transform' property does.
</p>
<!-- ======================================================================================================= -->
<h2 id="perspective-origin-property">
The <span class="prop-name">'perspective-origin'</span> Property
</h2>
<p>
The <span class="prop-name">'perspective-origin'</span> property
establishes the origin for the <em>perspective</em> property. It
effectively sets the X and Y position at which the viewer appears to be
looking at the children of the element.