angle/doc/BranchingAndRolling.md

How to Branch and Roll Chromium's ANGLE Dependency

ANGLE provides an implementation of OpenGL ES on top of other APIs (e.g. DirectX11, Vulkan). ANGLE uses (i.e. depends upon) other third-party software that comes from different repositories. ANGLE specifies its dependencies on a specific version of each of these other repositories in the ANGLE DEPS file.

Chromium relies upon ANGLE for hardware accelerated rendering and WebGL support. Chromium similarly specifies its dependency on a specific version of ANGLE in the Chromium repository's src/DEPS file.

This document describes how to update those dependencies, and, if necessary, create an ANGLE branch to correspond to a branched release of Chrome.

ANGLE's commit queue also runs browser-level tests which are hosted in the Chromium repository. To reduce the chance of a Chromium-side change breaking ANGLE's CQ, the version of Chromium against which ANGLE changes is also snapshotted, and rolled forward into ANGLE with appropriate testing.

Autorollers

At present, autorollers manage both the ANGLE roll into Chromium, and the Chromium roll into ANGLE. There is also an autoroller for ANGLE into Android AOSP. All of the ANGLE-related autorollers are documented in the ANGLE Wrangling documentation.

Manually rolling DEPS

As mentioned above, dependencies are encoded in DEPS files. The process to update a given dependency is as follows:

• Find the appropriate line in the relevant DEPS file that defines the dependency
• Change the git SHA-1 revision number to be that of the commit on which to depend upon (Note: use the full SHA-1, not a shortened version)
• You can find the SHA-1 for a particular commit with git log on the appropriate branch of the repository, or via a public repository viewer
• If using the ANGLE public repository viewer, you will need to select the branch whose log you wish to view from the list on the left-hand side, and then click on the "tree" link at the top of the resulting page. Alternatively, you can navigate to https://chromium.googlesource.com/angle/angle/+/<branch name>/ -- including the terminating forward slash. (e.g. https://chromium.googlesource.com/angle/angle/+/main/)

Rolling Vulkan Memory Allocator (VMA)

ANGLE and other Google projects (e.g. Skia, Chrome) use the open-source Vulkan Memory Allocator (VMA) library. As with with other external repositories, these projects do not directly use the upstream Vulkan Memory Allocator repository. Instead, a Google-local repository is used, which contains Google-local changes and fixes (e.g. changes to BUILD.gn). This Google-local repository repository contains the following key branches:

• upstream/master is automatically mirrored with the contents of the upstream VMA repository
• main is manually curated by Google, with a combination of upstream and Google-local changes

ANGLE's DEPS file points to a git SHA-1 revision of the main branch.

Manual rolls of the main branch currently involve rebasing all of the Google-local changes on top of newer upstream changes. The current process (done in 2022) is to:

• Revert all of the Google-local changes (i.e. with a single commit)
• Merge or cherry-pick all of the upstream changes
• Cherry-pick the Google-local changes on top
• Note: it may be possible to simply merge future upstream changes directly, without reverting the Google-local changes

Manual rolls of which SHA-1 revision the ANGLE's DEPS file points to is done via the process outlined above. Within an ANGLE build, you can navigate to the third_party/vulkan_memory_allocator directory, check out the main branch, and use git log to select the desired Git revision. Please note that cross-project coordination may be required when rolling VMA, as some projects (e.g. Chrome) builds itself with a single VMA version across Chrome, ANGLE, and Skia.

Note: When ANGLE is AutoRolled to the Android AOSP source tree, Google-local changes to the VMA BUILD.gn file will be converted to the ANGLE Android.bp file.

Branching ANGLE

Sometimes, individual changes to ANGLE are needed for a release of Chrome which has already been branched. If this is the case, a branch of ANGLE should be created to correspond to the Chrome release version, so that Chrome may incorporate only these changes, and not everything that has been committed since the version on which Chrome depended at branch time. Please note: Only ANGLE admins can create a new branch. To create a branch of ANGLE for a branched Chrome release:

• Determine what the ANGLE dependency is for the Chrome release by checking the DEPS file for that branch.
• Check out this commit as a new branch in your local repository.
  • e.g., for the Chrome 34 release at chrome/branches/1847, the ANGLE version is 4df02c1ed5. To check this commit out locally and create a new branch named 'mybranch' from this commit, use: git checkout -b mybranch 4df02c1ed5e97dd54576b06964b1da67ea30238e
• To create this new branch in the public repository, you'll need to push the branch to the special Gerrit reference location, 'refs/heads/'. You must be an ANGLE administrator to be able to push this new branch.
  • e.g., to use your local 'mybranch' to create a branch in the public repository called 'chrome_m34', use: git push origin mybranch:refs/heads/chrome_m34
  • The naming convention that ANGLE uses for its release-dedicated branches is 'chrome_m##'.