csswg-drafts/css-shapes-2/Overview.bs at 885ed4848166e6773b72f883486b95637f913376 · w3c/csswg-drafts · GitHub

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<pre class='metadata'>
Title: CSS Shapes Module Level 2
Status: ED
Work Status: Exploring
Shortname: css-shapes
Level: 2
Group: csswg
TR: https://www.w3.org/TR/css-shapes-2/
ED: https://drafts.csswg.org/css-shapes-2/
Editor: Rossen Atanassov, Microsoft Corporation, ratan@microsoft.com, w3cid 49885
Editor: Alan Stearns, Adobe Systems&#44; Inc., stearns@adobe.com, w3cid 46659
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: css2 (property) margin, css-display-3 (value) table
</pre>

<pre class='link-defaults'>
spec:css-masking-1; type: value
	text: nonzero
	text: evenodd
spec:css-shapes-1; type:property; text:shape-margin
</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>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>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>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.


<h2 id="basic-shape-functions">
Basic Shapes</h3>

	Add the final
	<a href="https://www.w3.org/TR/css-shapes/#basic-shape-functions">level 1</a>
	section.

<h3 id="supported-basic-shapes">
Supported Shapes</h3>

	Add the final
	<a href="https://www.w3.org/TR/css-shapes/#basic-shape-functions">level 1</a>
	section, with the following integrated.

	<dl>
		<dt>
			<pre class=prod>
				<dfn>path()</dfn> = path( [<<fill-rule>>,]? <<string>> )
			</pre>
		<dd dfn-type=value dfn-for="path()">
			<ul>
				<li>
					<dfn><<fill-rule>></dfn&g
6880
t; -
					The filling rule used
					to determine the interior
					of the path.
					See <a href="https://www.w3.org/TR/SVG/painting.html#FillRuleProperty">fill-rule</a> property
					in SVG for details.
					Possible values are <dfn>''nonzero''</dfn>
					or <dfn>''evenodd''</dfn>.
					Default value when omitted is ''nonzero''.
				<li>
					The <dfn><<string>></dfn>  represents an
					<a href="https://www.w3.org/TR/SVG11/paths.html#PathData">SVG Path data string</a>.
					The path data string must be conform
					to the grammar and parsing rules of SVG 1.1.
					The initial position is defined
					by the first “move to” argument
					in the path string.
					For the initial direction follow SVG 1.1.
			</ul>
	</dl>

	<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>

<h2 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="https://www.w3.org/TR/SVG/shapes.html">SVG basic shapes</a>
	or a <a href="https://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>

<h2 id="shapes-from-image">
Shapes from Image</h3>

	Add the final
	<a href="https://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).


<h2 id="shapes-from-box-values">
Shapes from Box Values</h2>

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

<h2 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>

<h3 id="shape-outside-property">
The 'shape-outside' Property</h4>

	Add the final
	<a href="https://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.

<h3 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>> | display
		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>
		Animation type: as defined for <<basic-shape>>, otherwise discrete
	</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 for=shape-inside>''outside-shape''</dfn></dt>
		<dd>
			The shape is computed based on
			the shape defined by the shape-outside
			and shape-margin properties.
		</dd>
	</dl>
	<dl>
		<dt><dfn>&lt;basic-shape&gt;</dfn></dt>
		<dd>
			The shape is computed based
			on the values of one of
			''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>
	<dl>
		<dt><dfn for=shape-inside>''display''</dfn></dt>
		<dd>
			The shape is computed based on the shape of the display
			as described in <a href="https://drafts.csswg.org/css-round-display">css-round-display</a>.
		</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).
	In other words,
	overflow continues outside
	the rectangular bounds of the element.</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>

	Issue: improve the illustration above,
	using text to show overflow instead of greeked boxes.

	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.


<h3 id="shape-image-threshold-property">
The shape-image-threshold Property</h4>

	Add the final
	<a href="https://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>.

<h3 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.

<h3 id="shape-margin-property">
The 'shape-margin' property</h4>

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

<h3 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
		Animation type: by computed value
	</pre>

	<div class="example">
		<p>A 'shape-padding' creating an offset
			from a circlular shape-inside.
			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.