Markus Stange [:mstange] Assignee
	Description • 6 years ago

At the moment, CompositorOGL always composites the entire window, no matter how much has actually changed.
LayerManagerCompositor already computes the changed region of the window, but we currently don't make use of that information on macOS, for two reasons:
 - We don't have an API to tell the window server which parts of the screen have changed.
 - We don't want to use the scissor rect to change only parts of the default framebuffer because our OpenGLContext is double buffered, and so the scissor rect computation would need to be aware of the number of buffers, which is brittle.

When using the CoreAnimation present path, we draw into an offscreen frame buffer. We have the full control over how to single buffer or double buffer, so we can be sure that we can compute a correct update rect for the frame buffer. Thus, the second point from above no longer applies.
So we should make use of the invalid region that LayerManagerComposite computes in order to save power when drawing into the default frame buffer.

Note that this still doesn't allow us to tell the system which parts of the screen need to be recomposited by the window server. But at least it saves some power in our side of the pipeline.

	Pulsebot
	Comment 3 • 5 years ago

Pushed by mstange@themasta.com:
https://hg.mozilla.org/integration/autoland/rev/cbbae09aa554
Limit CompositorOGL drawing to the invalid rect. r=mattwoodrow