I've been thinking about this in respect to WEBGL_dynamic_texture. The best idea I've come up with so far is an event the app can listen for which tells it that the canvas has reached the screen. The event payload would be the actual timestamp of the start of scanning the composited frame out to the display.Yup -- it's not that we don't want to measure composite, we're making an end-run around the fact that there exists no API for measuring composite. That API could also be somewhat complicated to define, because each browser could have a very different idea of what it actually means to composite. So, instead, I'm more interested in treating it as "overhead" -- I want to measure how much overhead a browser adds to each frame. This could be compositing overhead, it could be function call/JS bridge overhead, etc. That's where the second attempt comes into play, and it sounds like what gregg's already tried to implement.
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