Layout flushes cause spurious WebGL buffer swaps, causing flickering

[pcwalton]

This is the cause of the flickering on https://mdn.github.io/webgl-examples/tutorial/sample4/.

The problem is that the call to clientWidth after the gl.clear call flushes layout, which causes a recomposite of a blank canvas.

My intuition is that if the ReflowGoal is Query then we should somehow communicate that to script so that it won't cause a buffer swap inside WebGLRenderingContext::layout_handle.

@jdm What would you like to do here?

[pcwalton]

Actually I'm now leaning toward building up a list of dirty image keys during display list building, and flushing them all at once right before sending the DL off to WebRender. This would effectively do the same thing, but would maintain separation of concerns better because layout_handle wouldn't have to care about the layout goal.

[jdm]

That sounds like a reasonable solution to me. Is this the wrong repo for this issue, though?

[pcwalton]

Yes, transferring the issue. Oops!