EGL_ANGLE_experimental_present_path was enabled for fast rendering to SwapChain by ANGLE. But current gecko does not request ANGLE to render to SwapChain for WebRender. Then we do not need to use EGL_ANGLE_experimental_present_path anymore.

But when EGL_ANGLE_experimental_present_path is removed, rendering result of frame buffer is y flipped with ANGLE compared to other OpenGL implementation.

The following is fist check-in of EGL_ANGLE_experimental_present_path implementation.
https://github.com/google/angle/commit/2a63b3f8600bb9f90ff2870a0e1a23d251d45239

(In reply to Sotaro Ikeda [:sotaro] from comment #0)

Instead, we could use EGL_ANGLE_surface_orientation for Y flip. It is already used by chromium.

• https://cs.chromium.org/chromium/src/ui/gl/gl_surface_egl.cc?l=1210

Hmm, it seems that we could not use EGL_ANGLE_surface_orientation for non SwapChain EGLSurface :(

On chromium, GLSurface has a function FlipsVertically().By default, it returns false.

• https://cs.chromium.org/chromium/src/ui/gl/gl_surface.cc?l=187

But DirectCompositionSurfaceWin::FlipsVertically() returns true;

• https://cs.chromium.org/chromium/src/ui/gl/direct_composition_surface_win.cc?l=575

It is stored in Capabilities

• https://cs.chromium.org/chromium/src/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc?l=1407
• https://cs.chromium.org/chromium/src/content/browser/compositor/gpu_browser_compositor_output_surface.cc?l=33

The info seems to be used in SkiaOutputSurfaceImplOnGpu::SwapBuffers()

• https://cs.chromium.org/chromium/src/components/viz/service/display_embedder/skia_output_surface_impl_on_gpu.cc?l=846

It seems that gecko could do similar thing like comment 4.

gecko already has similar function. NativeLayer::SurfaceIsFlipped()
https://searchfox.org/mozilla-central/source/gfx/layers/NativeLayer.h#81

https://treeherder.mozilla.org/#/jobs?repo=try&revision=01a0bf06058f538969449729f481da40d155e83b

https://hg.mozilla.org/mozilla-central/rev/9277be3613ca