features:

move left to right smoothly: are the negative-space diamonds evenly-spaced? this helps measure mouse jitter.
bottom is raw input. top is extrapolated input
they alternate each frame. in fact, the top looks gray when still, but it isn't.
if an input is skipped, the output will double, and you'll see a bright white persistent triangle
if a frame is skipped, the triangles will flash once
you can't take a screenshot in fullscreen, but that is an anti-feature. I don't know why that happens.

left button to drag the vsync timepoint offset. it'll swap at a different time
right button to output all mouse positions

ctrl+1 twice: displays the render time, rather than the swap time. for seeing the latency. compare the line at first press (representing present time accuracy) and at second press. the difference represents latency to the accurate display



platform suggestions:
want that wayland proposal's swap mechanism. (tear after, good before)
want some way to know the porch positions. or at least the start of the delay
some way to know the vblank positions.
possible APIs:
	tearline + porch information
	vblank wakeup + porch information
	display wakeup
Windows's tearline API is good - it's both instant and very accurate. also giving horizontal position may help improve error, but it's not important.
	at least on Windows, both the overhead and accuracy of the tearline API are better than the wakeup