112 lines
4.6 KiB
C++
112 lines
4.6 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#ifndef GFX_FRAMELIMITER_H
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#define GFX_FRAMELIMITER_H
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#include "common/system.h"
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namespace Graphics {
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/**
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* A framerate limiter
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*
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* Ensures the framerate does not exceed the specified value
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* by delaying until all of the timeslot allocated to the frame
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* is consumed.
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* Allows to curb CPU usage and have a stable framerate.
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* If deferToVsync is set true (default), framerate will only be limited to the set value when hardware vsync is inactive, otherwise it will track Vsync directly.
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* If deferToVsync is set false, framerate will always be limited to the set value, whether or not hardware vsync is active.
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* In order for hardware vsync status detection to work correctly, initialize() must be called AFTER initGraphics; see below.
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*/
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class FrameLimiter {
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public:
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FrameLimiter(OSystem *system, const uint framerate, const bool deferToVsync = true);
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/**
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* Always call this after instantiating Screen & calling initGraphics(), to ensure Vsync status is detected correctly!
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*/
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void initialize();
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void initialize(const uint framerate);
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/**
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* Call immediately before starting game logic cycle, and immediately after previous screen->update(), if any.
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* Returns last frame duration.
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*/
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uint startFrame();
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/**
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* Call immediately after game logic cycle is completed, and immediately before screen->update().
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* If Vsync is inactive, will wait and return at the appropriate moment to call screen->update() in order to maintain the specified FPS.
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* If Vsync is active, will return immediately as screen->update() should automatically wait for the right moment.
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* Returns true if next frame is expected to be late.
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*/
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bool delayBeforeSwap();
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void pause(bool pause);
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/**
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* Return duration of last whole frame, including game logic, frame limiter or Vsync delay (if any), and screen redraw time.
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* Specifically, this is the time between the last two successive startFrame() calls.
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*/
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uint getLastFrameDuration() const {
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return _frameDuration;
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}
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/**
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* Return duration of last screen update
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* If Vsync is inactive, this value will just be the duration of the redraw process itself;
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* If Vsync is active, this value will encompass both the redraw time AND the delay between presenting the frame to redraw and the screen redraw actually starting.
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*/
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uint getLastDrawDuration() const {
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return _drawDuration;
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}
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/**
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* Return duration of last game logic loop
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* Specifically, this is the time from when startFrame() was last called to when delayBeforeSwap() was last called
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*/
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uint getLastLoopDuration() const {
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return _loopDuration;
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}
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/**
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* If true, framelimiter is active and applying _system->delayMillis(delay) to maintain the specified FPS, if valid.
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* If false, framelimiter is inactive, either because supplied FPS was invalid or because Vsync is active.
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* delayBeforeSwap() should still be called even if inactive, in order to ensure timers are updated correctly.
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*/
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bool isEnabled() const {
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return _enabled;
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}
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private:
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OSystem *_system;
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bool _enabled;
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bool _deferToVsync;
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uint _frameStart = 0; // Time at which screen update completed and startFrame() was called; start of next cycle of game logic
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uint _frameLimit = 0; // Target frame duration to achieve specified FPS
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uint _frameDuration = 0; // Duration of previous frame between successive startFrame() calls; total game logic, delay (if any) and screen update time
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uint _drawStart = 0; // Time at which delayBeforeSwap() returns
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uint _drawDuration = 0; // Measured screen update time
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uint _loopDuration = 0; // Duration of last game logic cycle, from when startFrame() was called to when delayBeforeSwap() was called
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int _delay = 0; // Time to delay before returning from delayBeforeSwap()
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uint _now = 0; // Current time
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};
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} // End of namespace Graphics
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#endif // GFX_FRAMELIMITER_H
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