csswg-drafts/css-shapes-2/Overview.bs at d7e717662ca9ba1d54a41d62cd097fe3b96ad79d · w3c/csswg-drafts · GitHub

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<h1>CSS Shapes Module Level 2</h1>

<pre class='metadata'>
Status: ED
Shortname: css-shapes
Level: 2
Group: csswg
TR: http://www.w3.org/TR/css-shapes-2/
ED: http://dev.w3.org/csswg/css-shapes-2/
Editor: Alan Stearns, Adobe Systems&#44; Inc., stearns@adobe.com
!Issues list: <a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&amp;product=CSS&amp;component=Shapes&amp;resolution=---&amp;cmdtype=doit">In Bugzilla</a>
Abstract: This draft contains the features of CSS relating to wrapping content around and inside shapes. It (implicitly for now) includes and extends the functionality of CSS Shapes Level 1 [[CSS-SHAPES]]. The main points of extension compared to level 1 include additional ways of defining shapes, defining an exclusion area using a shape, and restricting an element's content area using a shape.
Link Defaults: css21 (property) margin, css-display-3 (value) table
</pre>

<style type="text/css">
	.singleImgExample {
		display: block;
		margin: auto;
	}

	.example-table {
		table-layout: fixed;
		width: 100%;
	}

	.example-table tr td img {
		width: 90%;
	}
</style>


<h2 id="intro">
Introduction</h2>

	<em>This section is not normative.</em>

	Level 1 of this specification
	defined properties to control
	the geometry of an element's
	<span>float area</span>.
	This level defines how shapes apply to exclusions.
	It also includes a 'shape-inside' property
	for applying a shape
	to an element's content area.
	And finally it defines new ways
	of specifying shapes for all
	of these applications.


<h2 id="terminology">
Terminology</h2>

	<dfn>Exclusion area</dfn>

	The area used for excluding
	inline flow content
	around an exclusion box.
	The <span>exclusion area</span>
	is equivalent to the
	<a href="http://www.w3.org/TR/CSS2/box.html#box-dimensions">border box</a>
	for an exclusion box.
	This specification's 'shape-outside' property
	can be used to define arbitrary,
	non-rectangular <span>exclusion areas</span>.
	The 'shape-inside' property also defines
	an <span>exclusion area</span>,
	but in this case it is the area outside the shape
	that inline content avoids.


	<dfn>Float area</dfn>

	The area used for wrapping content
	around a float element.
	By default,
	the float area is
	the float element's
	<a href="http://www.w3.org/TR/CSS2/box.html#box-dimensions">margin box</a>.
	This specification's 'shape-outside' property
	can be used to define arbitrary,
	non-rectangular float areas.

	<dfn>Content area</dfn>

	The <a href="http://www.w3.org/TR/CSS2/box.html#box-dimensions">content area</a>
	is normally used for layout of the inline flow content of a box.


	<div class="issue-marker" data-bug_id="15089" data-bug_status="NEW">
		<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15089">Issue-15089</a>
		<div class="issue-details">
			<p class="short-desc">shrink-to-fit circle / shape</p>
		</div>
	</div>

<h2 id="shapes">
Shapes</h2>

	Shapes define arbitrary geometric contours
	around which inline content flows.
	The shape-outside property defines
	the <span>float area</span> for a float,
	and the exclusion area for an exclusion.


<h3 id="basic-shapes-from-svg-syntax">
Basic Shapes</h3>

	Add the final
	<a href="http://www.w3.org/TR/css-shapes/#basic-shapes-from-svg-syntax">level 1</a>
	section with a possible addition of path() and a rejiggered rectangle().

	<div class="issue-marker wrapper">
		<div class="issue-marker" data-bug_id="16448" data-bug_status="ASSIGNED">
			<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16448">Issue-16448</a>
			<div class="issue-details">
					<p class="short-desc">Should we revisit the decision to not allow SVG path syntax in the shape-inside, shape-outside properties</p>
			</div>
		</div>
	</div>

<h3 id='referencing-svg-shapes'>
Referencing SVG shapes</h4>

	An SVG shape can be referenced using the <code>url()</code> syntax.
	The shape can be any
	of the <a href="http://www.w3.org/TR/SVG/shapes.html">SVG basic shapes</a>
	or a <a href="http://www.w3.org/TR/SVG/paths.html">path element</a>.


<div class="example">
	<div style="float:right">
		<img alt="results of referencing SVG shapes" src="images/svg-shape-reference.png">
	</div>
	<code class="html"><pre>
&lt;style&gt;
div {
	height: 400px;
	width: 400px;
}
.in-a-circle {
	shape-outside: url(#circle_shape);
}

.in-a-path {
	shape-outside: url(#path-shape);
}

&lt;/style&gt;

&lt;svg ...&gt;
&lt;circle id="circle_shape" cx="50%" cy="50%" r="50%" /&gt;
&lt;path id="path-shape" d="M 100 100 L 300 100 L 200 300 z" /&gt;
&lt;/svg&gt;

&lt;div class="around-a-circle"&gt;...&lt;/div&gt;
&lt;div class="around-a-path"&gt;...&lt;/div&gt;
</pre></code>
</div>

<h3 id="shapes-from-image">
Shapes from Image</h3>

	Add the final
	<a href="http://www.w3.org/TR/css-shapes/#shapes-from-image">level 1</a>
	section.

	Issue: One <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16716">suggestion</a>
	is to define a shape based on an element's rendered content.
	This could have security implications.

	Issue: Another <a href="http://lists.w3.org/Archives/Public/www-style/2014Mar/0120.html">suggestion</a>
	is to add something to an image() function
	that determines the relevant pixels to use
	(both for defining a shape and for display).

<h3 id="declaring-shapes">
Declaring Shapes</h3>

	A shape can be declared with
	the 'shape-outside' property,
	with possible modifications
	from the 'shape-margin' property.
	The shape defined by
	the 'shape-outside'
	and 'shape-margin' properties
	changes the geometry
	of a float element's
	<span>float area</span>
	and an exclusion element's
	<span>exclusion area</span>.

	A shape can be declared with
	the 'shape-inside' property,
	with possible modifications
	from the 'shape-padding' property.
	The shape defined by
	the 'shape-inside'
	and 'shape-padding' properties
	defines an <span>exclusion area</span>
	that contributes
	to the element's <span>wrapping context</span>.
	The 'shape-inside' property applies
	to all block-level elements.

	<div class="example">

		The red box illustrates
		an exclusion element's content box,
		which is unmodified and subject
		to normal CSS positioning
		(here absolute positioning).

		<pre><code class="html">
	&lt;style type="text/css"&gt;
	.exclusion	{
			wrap-flow: both;
			position: absolute;
			top: 25%;
			left: 25%;
			width: 50%;
			height: 50%;
			shape-outside: circle(50% at 50% 50%);
			border: 1px solid red;
	}
	&lt;/style&gt;

	&lt;div style=”position: relative;”&gt;
	&lt;div class=”exclusion”&gt;&lt;/div&gt;
	Lorem ipsum dolor sit amet...
	&lt;/div&gt;
	</code></pre>
		<img class="singleImgExample"
		src="images/shapes_CSS2.1_MBP.png"
		alt="Example rendering of circle shape and box model."
		style="max-width:40%"/>
	</div>

<h4 id="shape-outside-property">
The 'shape-outside' Property</h4>

	Add the final
	<a href="http://www.w3.org/TR/css-shapes/#shape-outside-property">level 1</a>
	section with the change that
	shape-outside applies
	to block-level elements
	and has an effect
	if the element
	is an exclusion.

<h4 id="shape-inside-property">
The 'shape-inside' Property</h4>

	The 'shape-inside' property adds
	one or more exclusion areas
	to the element's wrapping context.
	This modifies the normal rectangular shape
	of the content area
	to a possibly non-rectangular wrapping area.
	The exclusion areas
	are defined by subtracting the shape
	from the element's content area.
	Any part of the shape outside
	the element's content area
	has no effect.

	<pre class='propdef'>
		Name: shape-inside
		Value: auto | outside-shape | [ <<basic-shape>> || shape-box ] | <<image>>
		Initial: auto
		Applies To: block-level elements
		Inherited: no
		Computed Value: computed lengths for <<basic-shape>>, the absolute URI for <<uri>>, otherwise as specified</td>
		Media: visual
		Animatable: as specified for <<basic-shape>>, otherwise no
	</pre>

	The values of this property have the following meanings:

	<dl>
		<dt><dfn for=shape-inside>''auto''</dfn></dt>
		<dd>
			The shape is computed based on the content box of the element.
		</dd>
	</dl>
	<dl>
		<dt><dfn>&lt;basic-shape&gt;</dfn></dt>
		<dd>
			The shape is computed based
			''inset()'', ''circle()'', ''ellipse()'' or ''polygon()''.
		</dd>
	</dl>
	<dl>
		<dt><dfn>&lt;uri&gt;</dfn></dt>
		<dd>
			If the &lt;uri&gt; references an SVG shape element,
			that element defines the shape.
			Otherwise, if the &lt;uri&gt; references an image,
			the shape is extracted and computed
			based on the alpha channel
			of the specified image.

			If the &lt;uri&gt; does not reference
			an SVG shape element or an image,
			the effect is as if the value ''auto'' had been specified.
		</dd>
	</dl>

	The 'shape-inside' property applies to floats.

	The 'shape-inside' property may not apply on some elements
	such as elements with a computed 'display' value of ''display/table''.

	<div class='figure'>
		<img alt="Content flowing with and without a shape-inside"
		     src="images/shape-inside-content.png"/>
		<p class="caption">Effect of shape-inside on inline content.</p>
	</div>

	Overflow content avoids
	the exclusion area(s) added
	by 'shape-inside' and 'shape-padding'
	(as well as any other exclusion areas
	in the element's wrapping context).</p>

	<div class='figure'>
		<img alt="Overflow interacting with rounded rect"
		     style="display:inline-block;vertical-align:top"
		     src="images/rounded-rect-overflow.png"/>
		<img alt="Overflow interacting with ellipse"
		     style="display:inline-block;vertical-align:top"
		     src="images/ellipse-overflow.png"/>
		<p class="caption">
			Overflow interacting with exclusion areas defined
			by 'shape-inside' and 'shape-padding'.
		</p>
	</div>

	When a shape-inside has a definite size
	(no percentages used in the shape's definition)
	an auto-sized element should use the shape
	as a constraint in determining its maximum size.


<h4 id="shape-image-threshold-property">
The shape-image-threshold Property</h4>

	Add the final
	<a href="http://www.w3.org/TR/css-shapes/#shape-image-threshold-property">level 1</a>
	section with the change that
	it applies to both <span>shape-inside</span>
	and <span>shape-outside</span>.

<h4 id="shape-image-source-type-property">
The shape-image-source-type Property</h4>

	Should we add an alpha/luminance switch
	to determine which values we use
	from the shape-image source?
	This could just be a keyword
	on the shape-image-threshold property.
	Whatever we go with should be compatible
	with the alpha/luminance switch from mask sources.

<h4 id="shape-margin-property">
The 'shape-margin' property</h4>

	Add the final
	<a href="http://www.w3.org/TR/css-shapes/#shape-margin-property">level 1</a>
	section with the change that it applies to exclusions.

<h4 id="shape-padding-property">
The 'shape-padding' Property</h4>

	The 'shape-padding' property adds padding to a shape-inside.
	This defines a new shape where every point
	is the specified distance from the shape-inside.
	This property takes on positive values only.

	<pre class='propdef'>
		Name: shape-padding
		Value: <<length>>
		Initial: none
		Applies To: block-level elements
		Inherited: no
		Computed Value: the absolute length
		Media: visual
		Animatable: as <a href="http://www.w3.org/TR/css3-transitions/#animtype-lpcalc">length, percentage, or calc</a>
	</pre>

	<div class="example">
		<p>A 'shape-padding' creating an offset
			from a circlular shape-inside.
			The light blue rectangles represent
			inline content affected
			by the shape created
			by the padding.</p>
		<img src="images/shape-padding.png"
			alt="Example of a shape-padding offset"/>
	</div>

	Note: The 'shape-padding' property
	only affects layout of content
	inside the element it applies to
	while the 'shape-margin' property
	only affects layout of content
	outside the element.