WebKitGTK+ 2.48 highlights

The WebKitGTK team has been working hard during the past six months and has recently released version 2.48 of the GTK port of WebKit. As is now tradition, here is an overview of the most important changes in this new stable release series.

Graphics and Rendering

The work on the graphics pipeline of WebKit continues, and a lot of improvements, refactors, bug fixes, and optimizations have happened under the hood. These changes bring both performance and rendering improvements, and are too many to list individually. Nonetheless, there are a number of interesting changes.

GPU Worker Threads

When GPU rendering with Skia is in use—which is the default—tiles will be rendered in worker threads, which has a positive impact on performance. Threads were already used when using the CPU for rendering.

Rendering Suspension

Rendering is now paused when the top-level window that contains a WebKitWebView is in a suspended state, freeing CPU/GPU cycles for other processes and reducing energy consumption when applications that use WebKitGTK are running in the background.

Canvas Improvements

The CanvasRenderingContext2D putImageData() and getImageData() methods have been optimized by preventing unnecessary buffer copies, resulting in improved performance and reduced memory usage.

CSS 3D Transforms

There have been several improvements to handling elements that use preserve-3d CSS transforms. On top of a modest performance improvement, the changes fixed rendering issues, making the implementation compliant with the CSS specification.

Damage Tracking

This release gained experimental support for collecting “damage” information, which tracks which parts of Web content produce visual changes in the displayed output. This information is then taken into account to reuse existing graphics buffers and repaint only those parts that need to be modified. This results better performance and less resource usage.

Note that this feature is disabled by default and may be previewed toggling the PropagateDamagingInformation feature flag.

GPU Process Beginnings

A new “GPU process” is now always built, but its usage is disabled by default at runtime. This is an experimental feature that can be toggled via the UseGPUProcessForWebGL feature flag, and as the name implies, at the moment this new auxiliary process only supports handling WebGL content.

The GPU process is a new addition to WebKit’s multiprocess model, in which isolated processes are responsible for different tasks: the GPU process will eventually be in charge of most tasks that make use of the graphics processing unit, in order to improve security by separating graphics handling from Web content and data access. At the same time, graphics-intensive work does not interfere with Web content handling, which may bring potential performance improvements in the future.

Multimedia

The MediaRecorder backend gained support for the WebM format and audio bitrate configuration. WebM usage requires GStreamer 1.24.9 or newer.

Video handling using the WebCodecs API no longer ignores the prefer-hardware option. It is used as a hint to attempt using hardware-accelerated GStreamer components. If that fails, software based codecs will be used as fallback.

The Web Speech API gained a new synthesis backend, using libspiel. The existing FLite-based backend is still chosen by default because the dependency is readily available in most distributions, but setting USE_SPIEL=ON at build time is recommended where libspiel may be available.

The GStreamer-GL sink can now handle DMA-BUF memory buffers, replacing the DMA-BUF sink in this way.

API Changes

The JavaScriptCore GLib API has a new jsc_value_new_promise() function to create Promise objects from native code.

Web Platform

The list of Web Platform features that are newly available in 2.48 is fairly lengthy, and includes the following highlights:

• JavaScript regular expression modifier flags.
• The Compression Streams API.
• The URLPattern API.
• Cross-document view transitions, and many improvements overall to the View Transitions support.
• The Web Components API gained support for CustomElementRegistry.
• The shape() CSS function.
• Support CSS width and height properties on MathML elements.
• Support CSS writing-mode: sideways-lr.
• Support scroll-to-text-fragment.

Some new functionality may disabled by default, but testable after toggling the corresponding feature flag.

• FileSystemWritableFileStream is available behind the flag of the same name.
• Support for CSS progress(), media-progress() and container-progress() functions—all part of the CSS, behind runtime flags CSSMediaProgressFunction and CSSContainerProgressFunction, respectively.

Other Noteworthy Changes

• The minimum required ICU version is now 70.1.
• Printing to PDF now sets the title in the metadata of the resulting PDF file.
• Reading of Remote Web Inspector protocol messages was optimized, resulting in a considerable speed-up for large messages.

The WebKitGTK team is already working on the 2.50 release, which is planned for September. In the meantime, you can expect stable updates for the 2.48 series through the usual channels.