I've read the source code of DispSync and so on, but it's too complicate.
What I've learnt is that "FrameCallback" is triggered by APP_VSYNC event, which may have time offset from HW_VSYNC. So, how could I know the precise time of HW_VSYNC?
If the time parameter of FrameCallback tells the APP_VSYNC time, where can I get the offset value between HW_VSYNC and APP_VSYNC so I can caculate the hardware vsync time?
IIRC, the timestamps reported by Choreographer are the APP_VSYNC times. As noted in the comments in Grafika's ScheduledSwapActivity:
* We coordinate with the display refresh using Choreographer. The SurfaceFlinger DispSync
* enhancements may cause the Choreographer-reported vsync time to be offset from the
* actual-reported vsync time (which may itself be slightly offset from the actual-actual
* vsync time). None of this is terribly important unless you care about A/V sync.
If A/V sync is your goal, you should probably be using the setPresentationTime() feature. See the comment above doFrame() for additional notes.
