resvg

resvg is an SVG rendering library.

Purpose

resvg can be used as:

• a Rust library
• a C library (see capi)
• a CLI application (see tools/rendersvg)

to render SVG files based on a static SVG Full 1.1 subset (see SVG support for details).

The core idea is to make a fast, small, portable, multiple-backend SVG library designed for edge-cases.

SVG can be rendered to a raster image or to a backend's canvas (e.g. to a QWidget via QPainter).

Why a new library?

resvg is competing with [librsvg], [QtSvg] and [Inkscape] (only as a CLI SVG-to-PNG converter).

One of the major differences from other rendering libraries is that resvg does a lot of preprocessing before rendering. It converts shapes to paths, resolves attributes, removes groups and invisible elements, fixes a lot of issues in malformed SVG files. Then it creates a simple render tree with all elements and attributes resolved. And only then it begins rendering. So it's very easy to implement a new rendering backend.

More details here.

resvg vs librsvg

librsvg is the main competitor to resvg. And even though librsvg itself is being rewritten in Rust, as resvg, the architecture of the library is completely different:

• librsvg is heavily tied to the [cairo] library
• librsvg is heavily tied to [GNOME], which makes it painful to distribute outside the Linux ecosystem
• librsvg doesn't produce an intermediate rendering tree
• librsvg has minimal support for edge cases, which leads to rendering errors

resvg vs Inkscape

Inkscape is often used to convert SVG to PNG, but it's not an actual competitor to resvg, since it's still a complete vector editor, not a tiny library. Also, it's very slow. But it has the best SVG support amongst others.

resvg vs QtSvg

Without a doubt, [QtSvg] is heavily used in [Qt] applications. But [QtSvg] itself is very limited. It officially supports only a tiny portion of the SVG Tiny 1.2 subset. In simple terms – it correctly renders only primitive SVG images. Also, it's deprecated.

SVG support

resvg is aiming to support only the static SVG subset; e.g. no a, script, view or cursor elements, no events and no animations.

A list of unsupported features can be found here.

SVG Tiny 1.2 and SVG 2.0 are not supported and not planned.

Results of the static subset of the SVG test suite:

Results of the resvg test suite:

You can find a complete table of supported features here. It also includes alternative libraries.

Performance

Note that all tested applications have a different SVG support, which impacts the performance.

Also, we do not test against Chrome, Firefox, Inkscape and Batik because they have a huge startup time.

• Elementary Icon Theme contains 3417 files.
• Qt backend is slow because QRasterPaintEngine is slow.

• The Oxygen icon theme contains 4947 files.
• All images were converted from .svgz to .svg beforehand.
• resvg is slower than librsvg because the Oxygen icon theme uses Gaussian blur heavily, which is expensive. And librsvg uses box blur optimization and multithreading, while resvg always uses a single-threaded IIR blur (at least for now).
• QtSvg doesn't support filter, clipPath, mask and pattern that are heavily used in the Oxygen icon theme. So it's actually very slow.

Project structure

• resvg – rendering backends implementation
  • usvg – an SVG simplification tool
  • svgdom – a DOM-like SVG tree
    • roxmltree – a DOM-like XML tree
    • xmlparser – an XML parser
    • svgtypes – SVG types parser and writer
  • rctree – a DOM-like tree
  • resvg-qt – minimal bindings to [Qt]

All other dependencies aren't written by me for this project.

Directory structure

• capi – C/FFI interface for resvg
• docs – basic documentation
• examples – usage examples for resvg as a library
• resvg-qt – minimal bindings to Qt used by resvg
• src – source code
• testing-tools – scripts used for testing
• tools – useful tools
• usvg – an SVG simplification library used by resvg

Safety

• The library must not panic. Any panic should be considered a critical bug and should be reported. There are only a few methods that can produce a panic.
• The core library structure (see above) does not use any unsafe, but since all backends are implemented via FFI, we are stuck with unsafe anyway. Also, usvg uses unsafe for fonts memory mapping.

License

resvg is licensed under the MPLv2.0.