Bug 218186 – CanvasCaptureMediaStreamTrack enables WebGL drawing buffer preserving and changes clear semantics

• Status: NEW
• Component: WebGL

[Kimmo Kinnunen]

CanvasCaptureMediaStreamTrack enables WebGL drawing buffer preserving

This changes de-facto observable behavior, as websites expect rAF to prepare the drawing buffer for display.

Web sites in general sometimes depend on the buffer clearing semantics.

[Kimmo Kinnunen]

Marking as blocking WebGL GPU Process work, since this is buggy that would need to be implemented in remote WebGL.

This should be instead fixed by introducing a canvas monitoring callback for drawing buffer prepare and calling that before the buffer is being prepared for display.

[Radar WebKit Bug Importer]

<rdar://problem/70946812>

[Kimmo Kinnunen]

So the purpose of the feature is to take the webgl canvas contents and send it through webrtc, if I understand correctly.

What the implementation does is:
1) Turn on WebGL "preserve drawing buffer" flag of the webgl context.
2) Takes a snapshot of the webgl canvas contents at random point in time after each modification when the execution drops to main loop
3) send that picture over webrtc

Steps 1 and 2 are not good.