Bug 218186

Summary:	CanvasCaptureMediaStreamTrack enables WebGL drawing buffer preserving and changes clear semantics
Product:	WebKit	Reporter:	Kimmo Kinnunen <kkinnunen>
Component:	WebGL	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal	CC:	dino, jonlee, webkit-bug-importer
Priority:	P2	Keywords:	InRadar
Version:	WebKit Local Build
Hardware:	Unspecified
OS:	Unspecified
See Also:	https://bugs.webkit.org/show_bug.cgi?id=218187 https://bugs.webkit.org/show_bug.cgi?id=217211

Description Kimmo Kinnunen 2020-10-26 06:36:01 PDT

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.

Comment 1 Kimmo Kinnunen 2020-10-26 06:38:43 PDT

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.

Comment 2 Radar WebKit Bug Importer 2020-11-02 05:36:19 PST

<rdar://problem/70946812>

Comment 3 Kimmo Kinnunen 2021-03-06 04:43:59 PST

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.