CSS Shapes Module Level 2

Editor’s Draft,

More details about this document
This version:
https://drafts.csswg.org/css-shapes-2/
Latest published version:
https://www.w3.org/TR/css-shapes-2/
Feedback:
CSSWG Issues Repository
Inline In Spec
Editors:
(Microsoft Corporation)
(Adobe Systems, Inc.)
Noam Rosenthal (Google)
Suggest an Edit for this Spec:
GitHub Editor

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.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

Please send feedback by filing issues in GitHub (preferred), including the spec code “css-shapes” in the title, like this: “[css-shapes] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list [email protected].

This document is governed by the 03 November 2023 W3C Process Document.

1. Introduction

This section is not normative.

Level 1 of this specification defined properties to control the geometry of an element’s float area. 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. Finally, it defines new ways of specifying shapes for all of these applications.

1.1. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

2. Terminology

exclusion area

The area used for excluding inline flow content around an exclusion box. The exclusion area is equivalent to the border box for an exclusion box. This specification’s shape-outside property can be used to define arbitrary, non-rectangular exclusion areas. The shape-inside property also defines an exclusion area, but in this case it is the area outside the shape that inline content avoids.

float area

The area used for wrapping content around a float element. By default, the float area is the float element’s margin box. This specification’s shape-outside property can be used to define arbitrary, non-rectangular float areas.

content area

The content area is normally used for layout of the inline flow content of a box.

3. Shapes

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

4. Basic Shapes

Add the final level 1 section.

4.1. Supported Shapes

Add the final level 1 sections.

4.1.1. The shape() Function

Add the final level 1 section.

5. Referencing SVG shapes

An SVG shape can be referenced using the url() syntax. The shape can be any of the SVG basic shapes or a path element.

results of referencing SVG shapes
<style>
div {
  height: 400px;
  width: 400px;
}
.in-a-circle {
  shape-outside: url(#circle_shape);
}

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

<svg ...>
  <circle id="circle_shape" cx="50%" cy="50%" r="50%" />
  <path id="path-shape" d="M 100 100 L 300 100 L 200 300 z" />
svg>

<div class="around-a-circle">...div>
<div class="around-a-path">...div>

6. Shapes from Image

Add the final level 1 section.

One suggestion is to define a shape based on an element’s rendered content. This could have security implications.

Another suggestion is to add something to an image() function that determines the relevant pixels to use (both for defining a shape and for display).

7. Fetching external shapes

To fetch an external resource for a shape, either an SVG or an image, given a CSS style declaration declaration, fetch a style resource given a value, with ruleOrDeclaration being declaration, destination "image", CORS mode "cors", and processResponse being the following steps given response res and null, failure or a byte stream byteStream: If byteStream is a byte stream, apply the image or SVG to the appropriate shape-accepting property.

Note: shapes require CORS mode as their effect is detected by the document.

8. Shapes from Box Values

Add the final level 1 section.

9. Declaring Shapes

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 float area and an exclusion element’s exclusion area.

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 exclusion area that contributes to the element’s wrapping context. The shape-inside property applies to all block-level elements.

The red box illustrates an exclusion element’s content box, which is unmodified and subject to normal CSS positioning (here absolute positioning).
<style type="text/css">
.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;
}
style>

<div style=”position: relative;”>
  <div class=”exclusion”>div>
  Lorem ipsum dolor sit amet...
div>

Example rendering of circle shape and box model.

9.1. The shape-outside Property

Add the final level 1 section with the change that shape-outside applies to block-level elements and has an effect if the element is an exclusion.

9.2. The shape-inside Property

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.

Name: shape-inside
Value: auto | outside-shape | [ || shape-box ] | | display
Initial: auto
Applies to: block-level elements
Inherited: no
Percentages: n/a
Computed value: computed lengths for , the absolute URL for , otherwise as specified
Canonical order: per grammar
Animation type: as defined for , otherwise discrete

The values of this property have the following meanings:

auto
The shape is computed based on the content box of the element.
outside-shape
The shape is computed based on the shape defined by the shape-outside and shape-margin properties.
The shape is computed based on the values of one of the functions.
If the references an SVG shape element, that element defines the shape. Otherwise, if the references an image, the shape is extracted and computed based on the alpha channel of the specified image.

If the does not reference an SVG shape element or an image, the effect is as if the value auto had been specified.

display
The shape is computed based on the shape of the display as described in css-round-display.

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 table.

Content flowing with and without a shape-inside
Effect of shape-inside on inline content.

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.

Overflow interacting with rounded rect Overflow interacting with ellipse
Overflow interacting with exclusion areas defined by shape-inside and shape-padding.

improve the illustration above, using text to show overflow instead of grey 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.

9.3. The shape-image-threshold Property

Add the final level 1 section with the change that it applies to both shape-inside and shape-outside.

9.4. The shape-image-source-type Property

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.

9.5. The shape-margin property

Add the final level 1 section with the change that it applies to exclusions.

9.6. The shape-padding Property

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.

Name: shape-padding
Value:
Initial: 0
Applies to: block-level elements
Inherited: no
Percentages: refer to the inline size of the containing block
Computed value: computed value
Canonical order: per grammar
Animation type: by computed value
Sets the padding of the shape to the specified value.
Example of a shape-padding offset
A shape-padding creating an offset from a circular shape-inside. The light blue rectangles represent inline content affected by the shape created by the padding.

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.

Privacy Considerations

No new privacy considerations have been reported on this specification.

Security Considerations

No new security considerations have been reported on this specification.

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with , like this: UAs MUST provide an accessible alternative.

Tests

Tests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative.


Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the [email protected] mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-BOX-4]
Elika Etemad. CSS Box Model Module Level 4. URL: https://drafts.csswg.org/css-box-4/
[CSS-DISPLAY-3]
Elika Etemad; Tab Atkins Jr.. CSS Display Module Level 3. URL: https://drafts.csswg.org/css-display/
[CSS-DISPLAY-4]
Elika Etemad; Tab Atkins Jr.. CSS Display Module Level 4. URL: https://drafts.csswg.org/css-display/
[CSS-IMAGES-3]
Tab Atkins Jr.; Elika Etemad; Lea Verou. CSS Images Module Level 3. URL: https://drafts.csswg.org/css-images-3/
[CSS-SHAPES]
Rossen Atanassov; Alan Stearns. CSS Shapes Module Level 1. URL: https://drafts.csswg.org/css-shapes/
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. URL: https://drafts.csswg.org/css-values-3/
[CSS-VALUES-4]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4. URL: https://drafts.csswg.org/css-values-4/
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 4. URL: https://drafts.csswg.org/css-writing-modes-4/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. URL: https://drafts.csswg.org/css2/
[CSS3-EXCLUSIONS]
Rossen Atanassov; Vincent Hardy; Alan Stearns. CSS Exclusions Module Level 1. URL: https://drafts.csswg.org/css-exclusions/
[FETCH]
Anne van Kesteren. Fetch Standard. Living Standard. URL: https://fetch.spec.whatwg.org/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119

Property Index

Name Value Initial Applies to Inh. %ages Anim­ation type Canonical order Com­puted value
shape-inside auto | outside-shape | [ || shape-box ] | | display auto block-level elements no n/a as defined for , otherwise discrete per grammar computed lengths for , the absolute URL for , otherwise as specified
shape-padding 0 block-level elements no refer to the inline size of the containing block by computed value per grammar computed value

Issues Index

One suggestion is to define a shape based on an element’s rendered content. This could have security implications.
Another suggestion is to add something to an image() function that determines the relevant pixels to use (both for defining a shape and for display).
improve the illustration above, using text to show overflow instead of grey boxes.
MDN

clip-path

In all current engines.

Firefox3.5+Safari9.1+Chrome55+
Opera?Edge79+
Edge (Legacy)NoneIENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

shape-image-threshold

In all current engines.

Firefox62+Safari10.1+Chrome37+
Opera?Edge79+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

shape-margin

In all current engines.

Firefox62+Safari10.1+Chrome37+
Opera?Edge79+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari10.3+Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

shape-outside

In all current engines.

Firefox62+Safari10.1+Chrome37+
Opera?Edge79+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

basic-shape

In all current engines.

Firefox54+Safari10.1+Chrome37+
Opera?Edge79+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?