Qt WebEngine and Qt Pdf Releases

Qt and Chromium combined

Qt WebEngine and Qt Pdf, also abbreviated as "QWE", consists of the API layer and adaptation layer for the Qt framework surrounding a specific version of Chromium.

Starting with Qt 6.8, Qt WebEngine was provided as a separate download outside of the main selection tree for Qt framework in the Qt Maintenance Tool. With Qt 6.12, the Qt WebEngine source code is decoupled as a sub-module from the Qt super-repository on Git, see Qt WebEngine Separate Release.

The goal for these separations is to gain more flexibility in releasing Qt WebEngine, and make releases more focused on security patches in Chromium and less driven by Qt Framework release cadence.

There is another Qt Extensions module which uses Chromium as a 3rd party dependency: Qt Pdf. Qt Pdf uses PDFium, which is an open-source C++ PDF rendering engine embedded directly into the Chromium project. The below sections cover the releasing of Qt Pdf as well, even if not explicitly mentioning it.

Note that a release of Qt WebEngine also contain the Qt WebView plugin for Qt WebEngine.

The main baseline and intake of security patches

Integrations of Chromium releases in Qt WebEngine follow two baselines. The Major version of Chromium used as the main baseline is listed as "Based on" in the first line of the file CHROMIUM_VERSION in the root folder of the Qt WebEngine repository, for example, like here:

Based on Chromium version: 140.0.7339.264
Patched with security patches up to Chromium version: 156.0.8078.74

This "Based on" version brings new features and other essential changes in Chromium that are important for Qt WebEngine.

According to the Chromium release scheme (see Chromium release schedule), the number "140" refers to the generation of Chromium releases as a main branch. It is used as a reference in Qt WebEngine for the main baseline of Chromium.

The "Patched with..." version on second line in the file CHROMIUM_VERSION lists the last version of Chromium used as a source of security patches. This line forms the security baseline of Chromium for Qt WebEngine, "74" in the above example. This number is important for users since it marks the integration point in Chromium with the most recent security patches.

Even though the goal is to integrate as many security patches as possible, not all patches are taken in along a security baseline. Some of them are not relevant for the Qt WebEngine API, while others have a low security ranking and are safe to be taken in later, during the next main baseline upgrade of Chromium.

Versioning

Like the Qt framework, Qt WebEngine uses semantic versioning, for instance, "6.140.0".

Major releases increment the major version number, resetting the minor version to zero. This number follows the major version of the Qt framework with which this Qt WebEngine is compatible. Here, it is Qt 6. Compared to the Qt framework, it does not reset the minor version number. See the next section for details about this.

Minor releases increment the minor version number, resetting the patch version number to zero. Minor versions contain the major version of Chromium as well as new functionality in Qt WebEngine. The "140" in the above example stands for the major version of Chromium used as the main baseline in the series of patch releases in this minor version.

Patch releases - also called maintenance releases - increment just the patch version number. Patch releases consist of bug fixes in Qt WebEngine, security fixes in Chromium, documentation fixes, and performance improvements.

Alignment with Qt framework regular and Long-Term Support releases

Qt WebEngine is a Qt Extension Module compatible and supported with a range of Qt framework releases.

Like with Qt framework releases prior to the separation in Qt 6.12.0, a release of Qt WebEngine could be used with Qt until the last supported Qt framework Long-Term Support release. For instance, the next Qt framework LTS release will be Qt 6.16. A release of Qt WebEngine provided after the Qt 6.16.0 release can also be used with Qt 6.12 LTS as well as with Qt 6.15.x, whereas this Qt WebEngine release will be the last for Qt 6.15.x, since Qt 6.15 is a regular release. A list of compatible Qt versions is provided in the release notes file release-note.md in the root folder of the Qt WebEngine repository

Release schedules

A released version of Qt WebEngine is supported and maintained for around 3 months, i.e., a maximum of six major versions of Chromium. After this, users should upgrade to the next maintained Qt WebEngine version. This migration is needed for Qt WebEngine to keep in-taking new security fixes and use new features in Chromium. The support and maintenance period for a given patch release of Qt WebEngine is also capped by the end of support of a Qt LTS release. After this point, users should upgrade to a newer Qt WebEngine and use a new Qt release.

Pre-built binaries

One path to use Qt WebEngine with different versions of the Qt framework is to use pre-built binaries. They are provided for the main desktop platforms via the Qt Maintenance Tool. They are linked in the selection tree to the nodes named after the Qt framework minor release they are built with.

Making your own builds

If pre-built binaries are not available for a version of the Qt framework, the user should create their own build, see Qt WebEngine.

Qt Pdf in the new versioning and releasing

All principles and rules in above sections apply to Qt Pdf as well. Certainly, Qt PDF is a Qt Extension on it own and brings its own API, see Qt Pdf

Commercial support

Terms and scope for commercial support for Qt WebEngine are the same as for the Qt framework, see [link].