diff options
| -rw-r--r-- | clutter/clutter/clutter-frame-clock.c | 59 |
1 files changed, 50 insertions, 9 deletions
diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c index 2f617d0a5..bcc6bae6a 100644 --- a/clutter/clutter/clutter-frame-clock.c +++ b/clutter/clutter/clutter-frame-clock.c @@ -266,18 +266,59 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock, last_presentation_time_us = frame_clock->last_presentation_time_us; next_presentation_time_us = last_presentation_time_us + refresh_interval_us; - /* Skip ahead to get close to the actual next presentation time. */ + /* + * However, the last presentation could have happened more than a frame ago. + * For example, due to idling (nothing on screen changed, so no need to + * redraw) or due to frames missing deadlines (GPU busy with heavy rendering). + * The following code adjusts next_presentation_time_us to be in the future, + * but still aligned to display presentation times. Instead of + * next presentation = last presentation + 1 * refresh interval, it will be + * next presentation = last presentation + N * refresh interval. + */ if (next_presentation_time_us < now_us) { - int64_t logical_clock_offset_us; - int64_t logical_clock_phase_us; - int64_t hw_clock_offset_us; + int64_t presentation_phase_us; + int64_t current_phase_us; + int64_t current_refresh_interval_start_us; + + /* + * Let's say we're just past next_presentation_time_us. + * + * First, we compute presentation_phase_us. Real presentation times don't + * have to be exact multiples of refresh_interval_us and + * presentation_phase_us represents this difference. Next, we compute + * current phase and the refresh interval start corresponding to now_us. + * Finally, add presentation_phase_us and a refresh interval to get the + * next presentation after now_us. + * + * last_presentation_time_us + * / next_presentation_time_us + * / / now_us + * / / / new next_presentation_time_us + * |--|-------|---o---|-------|--> presentation times + * | __| + * | |presentation_phase_us + * | | + * | | now_us - presentation_phase_us + * | | / + * |-------|---o---|-------|-----> integer multiples of refresh_interval_us + * | \__/ + * | |current_phase_us + * | \ + * | current_refresh_interval_start_us + * 0 + * + */ + + presentation_phase_us = last_presentation_time_us % refresh_interval_us; + current_phase_us = (now_us - presentation_phase_us) % refresh_interval_us; + current_refresh_interval_start_us = + now_us - presentation_phase_us - current_phase_us; - logical_clock_offset_us = now_us % refresh_interval_us; - logical_clock_phase_us = now_us - logical_clock_offset_us; - hw_clock_offset_us = last_presentation_time_us % refresh_interval_us; - - next_presentation_time_us = logical_clock_phase_us + hw_clock_offset_us; + next_presentation_time_us = + current_refresh_interval_start_us + + presentation_phase_us + + refresh_interval_us; } /* |