SVG 1.1 Support

Here is the support status of the different elements of SVG 1.1. The different sections correspond to those from the specification. You’ll find more simple information and tips on the documentation page.

Introduction

About SVG

No animations are supported in CairoSVG, as the output formats are mainly static. More generally, no real DOM support is offered, highly limiting the possibility of implementing features such as JavaScript support.

SVG MIME type, file name extension and Macintosh file type

CairoSVG can directly read gzip-compressed SVG files, relying on the .svg or .svgz input file extension to know if the file should be uncompressed.

SVG Namespace, Public Identifier and System Identifier

CairoSVG does not rely on the namespace URL, public identifier and system identifier URL. No DTD validation is provided.

Compatibility with Other Standards Efforts

Based on ElementTree, CairoSVG needs a real XML path and is not fault tolerant when parsing the XML. However, basic XML features such as namespaces are internally used. XLink is partially supported and should work for the standard usage.

Inline and external CSS is basically supported.

External XSLT, DOM, XML-SS, SMIL and Web Accessibility are not supported at all.

The basic Unicode features are supported, and should work for latin left-to-right-written languages. Other configurations are not tested yet.

Terminology

This document is not an RFC.

Definitions

This document does not really follow the definitions coming from this part (see previous chapter).

Concepts

Explaining the name: SVG

CairoSVG respects the scalable and vector parts of the format, when possible. PDF and PostScript formats allow vector graphics, and Cairo exports to these formats without rastering when possible.

Based on ElementTree or lxml, CairoSVG needs SVG files that are XML tree, and is not fault-tolerent. Namespaces are well supported.

Inline CSS is supported. External stylesheets are also supported when the tinycss and lxml libraries are available.

Important SVG concepts

Raster effects are not supported, because they are not supported by Cairo.

Fonts are also managed by Cairo, known to be just a ‘toy’ about fonts. Pango would be a much better choice, but it is a heavy dependency. Nevertheless, fonts can be selected in PDF documents.

Animations are not supported.

Options for using SVG in Web pages

CairoSVG can generate standard Cairo surfaces that can be used in Cairo-based web clients such as WeasyPrint.

Rendering Model

Introduction

CairoSVG generally follows the rendering model described by the specification.

The painters model

The painter model of Cairo, used by CairoSVG, is the same as the one from the specification. This includes alpha blending.

Rendering Order

The elements are rendered in the order of the SVG document.

How groups are rendered

Opacity values of groups are applied to the rendered inner elements. Simple masks, clips and filters are supported.

How elements are rendered

Opacity values of elements are applied. Simple masks, clips and filters are supported.

Types of graphics elements

Painting shapes and text

Elements are filled and stroked. Filling and stroking support plain colors, simple gradients and simple patterns, with or without opacity.

Painting raster images

Included raster images are supported by the Pillow package.

Filtering painted regions

3 filter effects are supported:

Clipping, masking and object opacity

Path clipping and alpha masking are supported. Clip and overflow of new viewports is not supported. Masks based on luminance are not supported.

Transparency, with simple alpha blending, is supported for semi-transparent colors and opacity values.

Parent Compositing

Transparency for the parent document are supported as long as the output format supports it. Semi-transparent PNGs can be generated.

Basic Data Types and Interfaces

Syntax

Thank you EBNF.

Basic data types

Angles are only supported when given in degrees, without explicit unit.

Colors are supported with rgb(), rgba(), #RGB, and #RRGGBB forms. Color keyword names are supported.

Frequencies are not supported.

Standard URI and IRI forms are supported, including fragment identifiers.

Numbers are supported, including exponents, integers and floats with the negative values.

Lengths are supported, with mm, cm, in, pt, pc, em, ex and % units.

Lists of various values are supported.

Times are not supported.

Real number precision

The real number precision is the same as the one of Python.

Recognized color keyword names

Color keyword names are supported.

Basic DOM interfaces

CairoSVG uses ElementTree internally, and has no real DOM interface.

Document Structure

Defining an SVG document fragment: the svg element

The svg tag is supported.

Grouping: the g element

The g tag is supported.

Defining content for reuse, and the defs element

The defs tag is supported for markers, gradients, patterns and paths reused in the document.

The desc and title elements

The desc and title tag are not supported.

The symbol element

The symbol tag is not supported.

The use element

The use tag supports local and distant (i.e. available through HTTP) external SVG files.

The image element

The image tag is supported by Pillow.

Conditional processing

Conditional processing is not supported.

Specifying whether external resources are required for proper rendering

The externalResourcesRequired attribute is not supported.

Common attributes

The id attribute is supported.

The xml:base attribute is supported for images.

DOM interfaces

The DOM interfaces are not supported.

Styling

Styling cannot be done with XSL. Inline and external CSS are basically supported.

Here are some properties that can be used as XML attributes:

Font properties:

Text properties:

Other properties for visual media:

Clipping, Masking and Compositing properties:

Filter Effects properties:

Gradient properties:

Interactivity properties:

Color and Painting properties:

Text properties:

Coordinate Systems, Transformations and Units

Introduction

CairoSVG renders its output on finite rectangular regions called viewport in the W3 recommendation, and Cairo surfaces in the application.

The viewport size must be given in the tag, as no negotiation process can be realized with the parent surface.

The coordinates transformations are correctly handled by CairoSVG, including nested transformations. Most of the transformations applied to external elements, including the ones in the gradients and the patterns, are supported.

The initial viewport

As the pages are not embedded, no negotiation process is possible when trying to determine the pages sizes.

The initial coordinate system

CairoSVG follows the recommendation about the initial coordinate system.

Coordinate system transformations

The coordinate system transformation given by the viewBox is correctly managed by CairoSVG. Rotations, translations and skews are correctly managed.

Nested transformations

Transformations can be nested in CairoSVG.

The transform attribute

The transform attribute parses and applies the matrix, translate, scale, rotate, skewX and skewY operations.

The viewBox attribute

The viewBox attribute is supported.

The preserveAspectRatio attribute

The preserveAspectRatio attribute is supported for svg elements, and not supported the other elements.

Establishing a new viewport

Only the svg element establishes a new viewport in CairoSVG.

Units

mm, cm, in, pt, pc, em, ex and percentages units are supported.

Object bounding box units

The objectBoundingBox attribute is not supported.

Intrinsic sizing properties of the viewport of SVG content

When the viewBox attribute is set to none, and no width or height is given, the intrinsic sizing properties of the viewport is not set, and the behaviour of CairoSVG is undetermined.

Geographic coordinate systems

No geographic coordinate system is managed in CairoSVG.

The svg:transform attribute

The transform attribute is correctly handled by CairoSVG.

DOM interfaces

The DOM interfaces are not supported.

Paths

Introduction

Paths are supported, including subpaths.

The path element

The main path attributes are supported.

Path data

The moveto, closepath, lineto, curveto, quadratic Bézier curveto and arcto commands are supported.

Distance along a path

Distance is calculated for text on a path.

DOM interfaces

The DOM interfaces are not supported.

Basic Shapes

Introduction

Basic shapes (rectangles, circles, ellipses, lines, polylines and polygons) are supported.

The rect element

Rectangles, including rounded corners, are supported.

The circle element

Circles are supported.

The ellipse element

Ellipses are supported.

The line element

Lines are supported.

The polyline element

Polylines are supported.

The polygon element

Polygons are supported.

DOM interfaces

The DOM interfaces are not supported.

Text

Introduction

The main features of text rendering are supported. The text and tspan tags are supported.

Characters and their corresponding glyphs

Characters are rendered by Cairo, text rendering relies on its simple rendering engine. There should be no ligatures, composite characters or glyph supstitutions.

Fonts, font tables and baselines

There’s no real baseline management with Cairo. The really simple vertical management doesn’t rely on the baseline.

The text element

The text element is supported, including its rotate attribute.

The tspan element

The tspan element is supported, including its rotate attribute.

The tref element

The tref element is supported.

Text layout

Simple text layout is managed for latin scripts, but not for bidirectional and vertical scripts.

Text rendering order

The glyphs are not rendered independently.

Alignment properties

Horizontal text alignment is supported for latin scripts.

Vertical text alignment is basically supported, but does no rely on the baseline and is only capable of top, middle or bottom alignment.

Font selection properties

The font-family, font-size, font-style and font-weight are basically supported, and should work as expected for common cases. The other attributes, including the font shorthand, are not supported.

Spacing properties

The spacing properties are not supported.

Text decoration

Text decoration is not supported.

Text on a path

Text on a path is supported, including the startOffset attribute.

Alternate glyphs

Alternate glyphs are not supported.

White space handling

White space are correctly handled and follow the rules given by the xml:space attribute.

Text selection and clipboard operations

Text selection is possible for PDF documents generated by CairoSVG, when the text is rendered with no extra effects including stroke and transformations.

DOM interfaces

The DOM interfaces are not supported.

Painting: Filling, Stroking and Marker Symbols

Introduction

Filling and stroking operations are supported for paths, texts and basic shapes. Markers are supported for paths, polylines, polygons and lines.

Specifying paint

Painting values are supported, with no ICC support. Gradients ant patterns are supported.

Fill properties

Filling operations are supported, including the fill-rule property.

Stroke properties

Stroking operations are supported, including all the stroke-* properties.

Controlling visibility

The display and visibility properties are supported.

Markers

Simple markers are supported, including the marker-* and orient attributes. Clipping thanks to the overflow property is not supported.

Rendering properties

Color interpolation and rendering properties are not supported. Shape, text and image rendering options are supported.

Inheritance of painting properties

Painting properties are supported.

DOM interfaces

The DOM interfaces are not supported.

Color

Introduction

CairoSVG handles the RGB part of this module.

The color property

The property as defined by the CSS2 specification is correctly handled.

Color profile descriptions

Color profiles are not handled.

DOM interfaces

The DOM interfaces are not supported.

Gradients and Patterns

Introduction

Gradients are generally correctly handled whereas patterns are poorly handled.

Gradients

Gradients are correctly handled, as long as Cairo can handle them. Some little details may not be rendered correctly, but you can rely on most of the generally used features.

Patterns

Patterns are poorly handled. Naive pattens are rendered, but simple features such as the viewBox property are ignored.

DOM interfaces

The DOM interfaces are not supported.

Clipping, Masking and Compositing

Introduction

Some of the clipping and masking features are handled. Simple alpha compositing and opacity are partially supported,

Simple alpha compositing

Alpha compositing is supported in Cairo, but color-interpolation and color-rendering properties are ignored.

Clipping paths

Path clipping is handled, but new viewports are not clipped.

Masking

Masking is handled with alpha-based masks, but not with luminance-based ones.

Opacity

The different *-opacity parameters are correctly handled.

DOM interfaces

The DOM interfaces are not supported.

Filter Effects

3 filter effects are supported:

Interactivity

No interactivity features are handled in CairoSVG.

Linking

Linking is not handled.

Scripting

Scripting is not handled.

Animation

Animations are not handled.

Fonts

Introduction

Simple font features, as described by the CSS2 specification, are handled, but Cairo has a poor support of complex features about fonts.

SVG fonts are not handled at all.

Overview of SVG fonts

SVG fonts are not handled.

The font element

The font element is ignored.

The glyph element

The glyph element is ignored.

The missing-glyph element

The missing-glyph element is ignored.

Glyph selection rules

Glyphs are not handled.

The hkern and vkern elements

The hkern and vkern elements are ignored.

Describing a font

Fonts, as defined by CSS2, are naively handled. Nevertheless, there is no real strategy to choose a font from its name, CairoSVG relies on Cairo for this choice.

DOM interfaces

The DOM interfaces are not supported.

Metadata

Metadata are ignored.