clutter/frame-clock: Add dispatch jitter to frame timing measurements
Dispatch jitter is how much the dispatch interval has changed between frames. It's a measure of sampling smoothness for events that are occurring at a higher rate than the screen is refreshing:
- Mouse movement
- Clients rendering at swap interval zero
- Keyframe animation position
Zero jitter is ideal but will practically never happen, and a jitter value of several thousand microseconds will be visible to the naked eye as stutter even if you're maintaining a perfect frame rate.
To make the numbers easier to interpret we also log the jitter as a percentage of the refresh interval.
Edited by Daniel van Vugt