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graphics/framelimiter.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "graphics/framelimiter.h"
+
+#include "common/util.h"
+
+namespace Graphics {
+
+FrameLimiter::FrameLimiter(OSystem *system, const uint framerate, const bool deferToVsync) :
+	_system(system),
+	_deferToVsync(deferToVsync) {
+	initialize(framerate);
+}
+
+void FrameLimiter::initialize() {
+	_enabled = (_frameLimit != 0) && !(_deferToVsync && _system->getFeatureState(OSystem::kFeatureVSync));
+	_frameDuration = _frameLimit;
+}
+
+void FrameLimiter::initialize(const uint framerate) {
+	_frameLimit = (framerate > 0) ? 1000.0f / CLIP<uint>(framerate, 1, 120) : 0;
+	initialize();
+}
+
+uint FrameLimiter::startFrame() {
+	_now = _system->getMillis();
+	if (_frameStart != 0) {
+		_frameDuration = _now - _frameStart;
+		_drawDuration = _now - _drawStart;
+	}
+	_frameStart = _now;
+	return _frameDuration;
+}
+
+bool FrameLimiter::delayBeforeSwap() {
+	_now = _system->getMillis();
+	_loopDuration = _now - _frameStart;
+	if (_enabled) {
+		//_delay = _frameLimit - _loopDuration;  // Original functionality, will tend to undershoot target framerate slightly due to finite screen.update() time.
+		_delay = _frameLimit - (_now - _drawStart); // Ensure that EXACTLY the specified frame duration has elapsed since last screen.update() was called.
+		if (_delay > 0)
+			_system->delayMillis(_delay);
+	}
+	_drawStart = _system->getMillis();
+	return (_delay < 0); // Check if frame is late
+}
+
+void FrameLimiter::pause(bool pause) {
+	if (!pause)
+		_frameStart = 0; // Ensure that the frame duration value is consistent when resuming
+}
+
+} // End of namespace Graphics