linux: osr: Default to use-angle=gl-egl and ozone-platform=x11 with shared textures

[agiyengar]

Summary:

When using off-screen rendering with shared texture support in CEF on Linux, rendering fails unless the command-line switch --use-angle=gl-egl is explicitly passed.

This happens because:

The GPU process imports shared textures using OzoneImageBacking::ProduceSkia().
https://source.chromium.org/chromium/chromium/src/+/main:gpu/command_buffer/service/shared_image/shared_image_manager.cc;l=394?q=SharedImageManager::ProduceSkia&ss=chromium

This path requires GetGLOzone() to return a valid object for the current Ozone platform (X11 or Wayland).
GetGLOzone() only works when ANGLE (via EGL) is enabled, i.e., when gl::GetGLImplementation() returns kGLImplementationEGLANGLE.

Without use-angle=gl-egl, GetGLOzone() returns nullptr, leading to SharedImageManager::ProduceSkia() failure and a broken rendering pipeline.

Wayland
https://source.chromium.org/chromium/chromium/src/+/main:ui/ozone/platform/wayland/gpu/wayland_surface_factory.cc;drc=a533a36dfe878045cd210166b8c3f1678fc987e7;bpv=1;bpt=1;l=218

X11
https://source.chromium.org/chromium/chromium/src/+/main:ui/ozone/platform/x11/x11_surface_factory.cc;l=181;drc=a533a36dfe878045cd210166b8c3f1678fc987e7

In addition we also see crashes caused by assertions on GTK macros like GDK_SCREEN_XDISPLAY, GDK_SCREEN_XNUMBER etc. The reason for the GTK assertions is the objects being returned are Wayland objects instead of X11. Example assertions
invalid cast from GdkWaylandScreen to GdkX11Screen etc.

Additional Context:
Even with --use-angle=gl-egl and --ozone-platform=x11, rendering on Linux with NVIDIA drivers fails in shared texture OSR mode due to limitations in the GBM backend:

Chromium uses gfx::BufferUsage::SCANOUT_CPU_READ_WRITE in the shared texture offscreen rendering path, which translates to the GBM flag combination GBM_BO_USE_LINEAR | GBM_BO_USE_SCANOUT | GBM_BO_USE_TEXTURING.
https://source.chromium.org/chromium/chromium/src/+/main:ui/gfx/linux/gbm_util.cc;l=24?q=GBM_BO_USE_LINEAR&ss=chromium

This combination does not work on Nvidia. We need to change this to GBM_BO_USE_RENDERING which works correctly on AMD as well.

Proposal:

Add logic in CEF to automatically append --use-angle=gl-egl and ozone-platform=X11 when:

off_screen_rendering_enabled is true, and

GPU compositing is enabled (shared texture mode), and

the switches --use-angle and ozone-backend are not already present.

This would ensure that both vulkan and EGL based applications can render images correctly.

[agiyengar]

PR here #3954

[1zun4]

Hi. Could you give me some insight or a code example on how to do OSR with shared texture on Linux? I'm currently working on the following pull request: chromiumembedded/java-cef#509. Even though the bindings work correctly and I can convert a D3D11 texture into an OpenGL texture on Windows, I'd also like to accomplish support for Linux.

If I understand Angle Renderer correctly, I might even be able to get a native OpenGL texture right away? Appreciate the help and glad I'm not the only one trying to get shared textures to work on different platforms.

[agiyengar]

PR here https://bitbucket.org/chromiumembedded/cef/pull-requests/917/diff

[agiyengar]

Hi @1zun4 happy to help!

For OSR with shared textures on Linux, you’ll want to:

1. Enable shared texture mode in CEF (via --use-angle and --ozone-platform).

2. Implement OnAcceleratedPaint. In shared texture mode, CEF hands you either:
   a dma-buf file descriptor or a shared image handle (depending on platform)

3. On Linux, you’ll typically work with a dma buf fd as below:

EGLint attribs[] = {
EGL_WIDTH, width,
EGL_HEIGHT, height,
EGL_LINUX_DRM_FOURCC_EXT, GBM_FORMAT_ARGB8888,
EGL_DMA_BUF_PLANE0_FD_EXT, dma_buf_fd,
EGL_DMA_BUF_PLANE0_OFFSET_EXT, 0,
EGL_DMA_BUF_PLANE0_PITCH_EXT, stride,
EGL_NONE
};

EGLImageKHR image = eglCreateImageKHR(
egl_display,
EGL_NO_CONTEXT,
EGL_LINUX_DMA_BUF_EXT,
nullptr,
attribs);

4. Bind the EGL image as a texture
   glBindTexture(GL_TEXTURE_2D, texture_id);
   glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, image);

5. Render as usual.
   The critical part is negotiating dmabuf modifiers for compatibility with the GPU driver.

[magreenblatt]

Fixed in cf5fddc