clutter/frame-clock: Simplify next_presentation_time_us calculation
When more than one refresh interval has passed since last_presentation_time_us. I honestly can't tell if the previous calculation was correct or not, but I'm confident the new one is, and it's simpler. v2: * ASCII art diagram didn't make sense anymore, try to improve (Ivan Molodetskikh) Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3330>
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@ -511,48 +511,29 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock,
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if (next_presentation_time_us < now_us)
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if (next_presentation_time_us < now_us)
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{
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{
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int64_t presentation_phase_us;
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int64_t current_phase_us;
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int64_t current_phase_us;
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int64_t current_refresh_interval_start_us;
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/*
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/*
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* Let's say we're just past next_presentation_time_us.
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* Let's say we're just past next_presentation_time_us.
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*
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*
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* First, we compute presentation_phase_us. Real presentation times don't
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* First, we calculate current_phase_us, corresponding to the time since
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* have to be exact multiples of refresh_interval_us and
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* the last integer multiple of the refresh interval passed after the last
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* presentation_phase_us represents this difference. Next, we compute
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* presentation time. Subtracting this phase from now_us and adding a
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* current phase and the refresh interval start corresponding to now_us.
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* refresh interval gets us the next possible presentation time after
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* Finally, add presentation_phase_us and a refresh interval to get the
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* now_us.
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* next presentation after now_us.
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*
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*
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* last_presentation_time_us
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* last_presentation_time_us
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* / next_presentation_time_us
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* / next_presentation_time_us
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* / / now_us
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* / / now_us
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* / / / new next_presentation_time_us
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* / / / new next_presentation_time_us
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* |--|-------|---o---|-------|--> presentation times
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* |-------|---o---|-------|--> possible presentation times
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* | __|
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* \_/ \_____/
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* | |presentation_phase_us
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* / \
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* | |
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* current_phase_us refresh_interval_us
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* | | now_us - presentation_phase_us
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* | | /
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* |-------|---o---|-------|-----> integer multiples of refresh_interval_us
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* | \__/
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* | |current_phase_us
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* | \
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* | current_refresh_interval_start_us
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* 0
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*
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*/
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*/
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presentation_phase_us = last_presentation_time_us % refresh_interval_us;
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current_phase_us = (now_us - last_presentation_time_us) % refresh_interval_us;
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current_phase_us = (now_us - presentation_phase_us) % refresh_interval_us;
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next_presentation_time_us = now_us - current_phase_us + refresh_interval_us;
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current_refresh_interval_start_us =
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now_us - presentation_phase_us - current_phase_us;
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next_presentation_time_us =
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current_refresh_interval_start_us +
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presentation_phase_us +
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refresh_interval_us;
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}
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}
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if (frame_clock->is_next_presentation_time_valid)
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if (frame_clock->is_next_presentation_time_valid)
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