Highlights of WebKitGTK+ 2.50

The WebKitGTK team has released this fall the 2.50 series of the GTK port of the WebKit engine after six months of hard work. Let’s have a deeper look at some of the most interesting changes in this release series!

Improved rendering performance

For this series, the threaded rendering implementation has been switched to use the Skia API. What has changed is the way we record the painting commands for each layer. Previously we used WebCore’s built-in mechanism (DisplayList) which is not thread-safe, and led to obscure rendering issues in release builds and/or sporadic assertions in debug builds when replaying the display lists in threads other than the main one. The DisplayList usage was replaced with SkPictureRecorder, Skia’s built-in facility, that provides similar functionality but in a thread-safe manner. Using the Skia API, we can leverage multithreading in a reliable way to replay recorded drawing commands in different worker threads, improving rendering performance.

An experimental hybrid rendering mode has also been added. In this mode, WebKitGTK will attempt to use GPU worker threads for rendering but, if these are busy, CPU worker threads will be used whenever possible. This rendering mode is still under investigation, as it’s still unclear whether the improvements are substantial enough to justify the extra complexity.

Damage propagation to the system compositor, which was added during the 2.48 cycle but remained disabled by default, has now been enabled. The system compositor may now leverage the damage information for further optimization.

Vertical writing-mode rendering has also received improvements for this release series.

Changes in Multimedia support

When available in the system, WebKit can now leverage the XDG desktop portal for accessing capture devices (like cameras) so that no specific sandbox exception is required. This provides secure access to capture devices in browser applications that use WebKitGTK.

Managed Media Source support has been enabled. This potentially improves multimedia playback, for example in mobile devices, by allowing the user agent to react to changes in memory and CPU availability.

Transcoding is now using the GStreamer built-in uritranscodebin element instead of GstTranscoder, which improves stability of the media recording that needs transcoding.

SVT-AV1 encoder support has been added to the media backend.

Web Platform support

As usual, changes in this area are extensive as WebKit constantly adopts, improves, and supports new Web Platform features. However, some interesting changes in this release cycle include:

• The new CookieStore API is now supported.
• ManagedMediaSource is also supported now.
• CSS container-progress() support is now enabled by default.
• CSS text-wrap-style: pretty is enabled by default.
• CSS font-family: math is now supported.
• CSS border-shape also gained further support.
• CSS Animation: overallProgress support is now enabled by default.
• HTML auto-expanding <details> are now enabled by default.
• CSS hidden=”until-found” is also now enabled by default.

API changes

• The WebKitSettings:enable-hyperlink-auditing option has been deprecated. This feature is now always enabled.
• The webkit_web_view_get_theme_color() function has been added to allow querying the theme color declared by the content loaded in a web view. The corresponding WebKitWebView:theme-color property is available as well, which allows using the notify signal to watch for theme color changes.

What’s new for WebKit developers?

WebKit now suppors sending tracing marks and counters to Sysprof. Marks indicate when certain events occur, and their duration; while counters track variables over time. Together, these allow developers to find performance bottlenecks and monitor internal WebKit performance metrics like frame rates, memory usage, and more. This integration enables developers to analyze the performance of applications, including data for WebKit alongside system-level metrics, in a unified view. For more details see this article, which also details how Sysprof was improved to handle the massive amounts of data produced by WebKit.

Finally, GCC 12.2 is now the minimum required version to build WebKitGTK. Increasing the minimum compiler version allows us to remove obsolete code and focus on improving code quality, while taking advantage of new C++ and compiler features.

Looking forward to 2.52

The 2.52 release series will bring even more improvements, and we expect it to be released during the spring of 2026. Until then!