chromium

Chromium

This folder contains a patch for Chromium to compile with OpenXR support under Linux, loosely based on this PR.

How to compile

In order to apply and compile this patch, it's important that you are able to compile Chromium yourself. For this follow the steps over at: https://chromium.googlesource.com/chromium/src/+/main/docs/linux/build_instructions.md

Once you have the Chromium code base locally, apply the patch using the the following command (or use git apply):

git am /path/to/webxr-linux/chromium/webxr-linux-vulkan-2copy.patch

Note These patches were made on top of Chromium 117, commit d84f1a0ebf4e90528407c3e8a606a7b57f336a36, and hopefully apply cleanly to more recent commits as well.

Once applied, build using autoninja. In order for chromium to find your configured OpenXR runtime make sure to launch it with the --no-sandbox flag

./chrome --no-sandbox

Other relevant things to mention

• A copy of this patch is included to fix an issue preventing texture sharing.
• Two texture copies are involved in the frame transfer: an ANGLE->Vulkan copy in the GPU process and a Vulkan->OpenXR copy in the XR process.
  • A call to GLES2Interface::Finish() is used to synchronize these two copies. A GPU-side semaphore would offer significantly reduced frametimes, but Chromium doesn't seem to offer a working IPC interface for them under Linux (the provided gfx::GpuFence interface is only implemented under Windows and Android).
  • The second copy is needed due to OpenXR's swapchain textures not being suitable for inter-process sharing.
• There are different ways for the transport to take place, either SUBMIT_AS_TEXTURE_HANDLE, SUBMIT_AS_MAILBOX_HOLDER or DRAW_INTO_TEXTURE_MAILBOX.
  • This patch exclusively uses the SUBMIT_AS_MAILBOX_HOLDER mode. A future patch adding DRAW_INTO_TEXTURE_MAILBOX support could allow omitting a texture copy, improving performance.
• As of July 2023, SteamVR's OpenXR implementation has a bug which deadlocks the process on instance destroy or exit, preventing subsequent WebXR sessions from starting after the first one finishes. See this issue for more details.