Bug 240380 – Capturing a canvas that is not in the DOM can lead to erratic frame rates or no frame emission at all

• Status: RESOLVED
• Resolution: FIXED
• Component: Media

[youenn fablet]

Capturing a canvas that is not in the DOM can lead to erratic frame rates or no frame emission at all

[Radar WebKit Bug Importer]

<rdar://problem/93239022>

[Said Abou-Hallawa]

Test case is https://jsfiddle.net/0b3dqxeg/

[Claudio Destro]

Hi hope this helps:

in our solution, canvas with CSS fixed position works

[Claudio Destro]

Example missing (sorry):

modify the test case to:

<canvas id="canvas2" style="position: fixed; bottom: 0; right: 0; width: 100px"></canvas>

videos still not playing in 15.4 desktop (they show a red background and nothing else happens)

[youenn fablet]

I did some investigations:
- CanvasCaptureMediaStreamTrack::Source::canvasChanged is correctly called each time the not-in-dom canvas is changed but it returns early due to m_canvas->renderingContext()->needsPreparationForDisplay() returning true.
- Normally, the page will call updateRendering which will make the actual preparation happening, which in turn will tell CanvasCaptureMediaStreamTrack::Source to generate a frame. This is what happens when canvas is in the DOM. When canvas is not in the DOM, Page::updateRendering is not called as often and this impacts the canvas track frame rate.

[Dan Glastonbury]

Pull request: https://github.com/WebKit/WebKit/pull/901

[EWS]

Committed r294864 (250996@main): <https://commits.webkit.org/250996@main>

Reviewed commits have been landed. Closing PR #901 and removing active labels.