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68 lines
1.6 KiB
C++
68 lines
1.6 KiB
C++
//
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// VSyncPredictor.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 14/06/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#ifndef VSyncPredictor_hpp
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#define VSyncPredictor_hpp
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#include "TimeTypes.hpp"
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namespace Time {
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/*!
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For platforms that provide no avenue into vsync tracking other than block-until-sync,
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this class tracks: (i) how long frame draw takes; and (ii) the apparent frame period; in order
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to suggest when you should next start drawing.
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*/
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class VSyncPredictor {
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public:
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void begin_redraw() {
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redraw_begin_time_ = nanos_now();
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}
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void end_redraw() {
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const auto redraw_length = nanos_now() - redraw_begin_time_;
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redraw_period_ =
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((redraw_period_ * 9) +
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((redraw_length) * 1)) / 10;
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}
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void announce_vsync() {
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const auto vsync_time = nanos_now();
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if(last_vsync_) {
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// Use an IIR to try to converge on frame times.
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vsync_period_ =
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((vsync_period_ * 9) +
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((vsync_time - last_vsync_) * 1)) / 10;
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}
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last_vsync_ = vsync_time;
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}
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void pause() {
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last_vsync_ = 0;
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}
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Nanos suggested_draw_time() {
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// TODO: this is a very simple version of how this calculation
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// should be made. It's tracking the average amount of time these
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// things take, therefore will often be wrong. Deviations need to
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// be accounted for.
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return last_vsync_ + vsync_period_ - redraw_period_;
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}
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private:
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Nanos redraw_begin_time_ = 0;
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Nanos last_vsync_ = 0;
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Nanos vsync_period_ = 1'000'000'000 / 60; // Seems like a good first guess.
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Nanos redraw_period_ = 0;
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};
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}
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#endif /* VSyncPredictor_hpp */
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