Event loop best practices / eglSwapBuffers+ALooper sync / touch+frame lag while animating

[Loren Brichter]

I notice that my GL rendering seems to fall behind by a frame or two while I'm animating. There are two modes to my event loop:

Non-animating:

1. Block on ALooper for an event

2. Drain ALooper until empty

3. Update scene

4. Draw

5. Swap

Animating: (same as non-animating, with step (1) eliminated

1. Drain ALooper until empty

2. Update scene

3. Draw

4. Swap

I have a very simple test scene (a single polygon that you can drag around with your finger). In the non-animating case, it sticks to your finger well. In the animating case, it seems to fall behind by _at least_ an extra frame as I drag the polygon around.

Two hacks appear to mitigate this: (a) glFinish after the Swap, never lets things get too far behind, (b) short usleep before the Drain [in theory this would give the system more time to present the last frame or more time to let fresh touch events queue up before I start draining them... not exactly sure which is the issue].

Has anyone experienced a similar issue (is triple buffering kicking in? possible to disable?) or are there docs on how to coordinate between a vsync'd swapbuffer call and draining the event queue to minimize latency?

Thanks,

Loren