osr: cefclient: mac: OnAcceleratedPaint/OnPaint is not called with external-begin-frame

[csmoe]

Describe the bug

To Reproduce
Steps to reproduce the behavior:

1. Download the latest example app from https://cef-builds.spotifycdn.com/index.html#macosarm64
2. ./cefclient.app/Contents/MacOS/cefclient --off-screen-rendering-enabled --url=https://www.google.com --external-begin-frame-enabled --shared-texture-enabled
3. The window will remain blank

Versions (please complete the following information):

• OS: macOS 26.0.1 M1 pro
• CEF Version: 142.0.14+gceaf578+chromium-142.0.7444.163

cc @reitowo sorry for bothering you

[csmoe]

This bug is bisected to 77c1e82 , the previous commit's cefclient works fine.

[reitowo]

Yeah, that's when the new accelerated OSR is back. I think it might be that the bool flag didn't pass all the way down. Could you try to analyze that part of the code?

[csmoe]

Okay, I'll track down that.

[csmoe]

* thread #1, name = 'CrBrowserMain', queue = 'com.apple.main-thread', stop reason = breakpoint 3.2
    frame #0: 0x000000016065a58c libui_compositor.dylib`ui::Compositor::Compositor(this=0x00000007cc11a800, frame_sink_id=0x000000016fdf92a8, context_factory=0x00000007cc4252c0, task_runner=(ptr_ = 0x00000007ccdd71b0), enable_pixel_canvas=false, use_external_begin_frame_control=true, force_software_compositor=false, enable_compositing_based_throttling=false, memory_limit_when_visible_mb=0) at compositor.cc:107:34
   104 	      force_software_compositor_(force_software_compositor),
   105 	      layer_animator_collection_(this),
   106 	      is_pixel_canvas_(enable_pixel_canvas),
-> 107 	      lock_manager_(task_runner) {
   108 	  DCHECK(context_factory_);
   109 	  auto* host_frame_sink_manager = context_factory_->GetHostFrameSinkManager();
   110 	  host_frame_sink_manager->RegisterFrameSinkId(
[78380:480658:1119/154441.720410:INFO:child_thread_impl.cc(973)] ChildThreadImpl::EnsureConnected()
[78381:480677:1119/154442.010429:INFO:child_thread_impl.cc(973)] ChildThreadImpl::EnsureConnected()
[78382:480678:1119/154442.081556:INFO:child_thread_impl.cc(973)] ChildThreadImpl::EnsureConnected()
(lldb) frame var
(ui::Compositor *) this = 0x00000007cc11a800
(const viz::FrameSinkId &) frame_sink_id = 0x000000016fdf92a8 (client_id_ = 0, sink_id_ = 1)
(ui::ContextFactory *) context_factory = 0x00000007cc4252c0
(scoped_refptr<base::SingleThreadTaskRunner>) task_runner = (ptr_ = 0x00000007ccdd71b0)
(bool) enable_pixel_canvas = false
(bool) use_external_begin_frame_control = true
(bool) force_software_compositor = false
(bool) enable_compositing_based_throttling = false
(size_t) memory_limit_when_visible_mb = 0

I breakpointed at constructor of ui::Compositor

cef/libcef/browser/osr/render_widget_host_view_osr.cc

Line 251 in 6c5520c

compositor_ = std::make_unique<ui::Compositor>(

, the flag was true indeed.

[csmoe]

Turns out that cefclient doesn't implement SendExternalBeginFrame on mac from the beginning which hardcoded the external_begin_frame always as false, the new gpu osr commit makes the flag configurable

[reitowo]

Yeah, that's possible. I probably changed that accidentally, maybe you can try to implement one :) I remember the mac port of cefclient + offscreen rendering is kind of "just work", e.g. rendering IOSurface on that OpenGL thing very slow.