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engines/ags/engine/ac/timer.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 "common/std/thread.h"
+#include "ags/engine/ac/timer.h"
+#include "ags/shared/core/platform.h"
+#include "ags/engine/ac/sys_events.h"
+#include "ags/engine/platform/base/ags_platform_driver.h"
+#include "ags/ags.h"
+#include "ags/globals.h"
+
+namespace AGS3 {
+
+namespace {
+const auto MAXIMUM_FALL_BEHIND = 3; // number of full frames
+}
+
+std::chrono::microseconds GetFrameDuration() {
+	if (_G(framerate_maxed)) {
+		return std::chrono::microseconds(0);
+	}
+	return _G(tick_duration);
+}
+
+int setTimerFps(int new_fps) {
+	assert(new_fps >= 0);
+	if (new_fps <= 0)
+		return _G(framerate);
+	int old_fps = _G(framerate);
+	_G(tick_duration) = std::chrono::microseconds(1000000LL / new_fps);
+	_G(framerate) = new_fps;
+	_G(framerate_maxed) = new_fps >= 1000;
+
+	// Update next frame time
+	_G(next_frame_timestamp) = _G(last_tick_time) + _G(tick_duration);
+	return old_fps;
+}
+
+bool isTimerFpsMaxed() {
+	return _G(framerate_maxed);
+}
+
+void WaitForNextFrame() {
+	const auto now = AGS_Clock::now();
+	const auto frameDuration = GetFrameDuration();
+
+	// early exit if we're trying to maximise framerate
+	if (frameDuration <= std::chrono::milliseconds::zero()) {
+		_G(last_tick_time) = _G(next_frame_timestamp);
+		_G(next_frame_timestamp) = now;
+		// suspend while the game is being switched out
+		while (_G(game_update_suspend) && !_G(want_exit) && !_G(abort_engine)) {
+			sys_evt_process_pending();
+			_G(platform)->YieldCPU();
+		}
+		return;
+	}
+
+	// jump ahead if we're lagging
+	if (_G(next_frame_timestamp) < (now - MAXIMUM_FALL_BEHIND * frameDuration)) {
+		_G(next_frame_timestamp) = now;
+	}
+
+	if (_G(next_frame_timestamp) > now) {
+		auto frame_time_remaining = _G(next_frame_timestamp) - now;
+		std::this_thread::sleep_for(frame_time_remaining);
+	}
+
+	_G(last_tick_time) = _G(next_frame_timestamp);
+	_G(next_frame_timestamp) += frameDuration;
+
+	// suspend while the game is being switched out
+	while (_G(game_update_suspend) && !_G(want_exit) && !_G(abort_engine)) {
+		sys_evt_process_pending();
+		_G(platform)->YieldCPU();
+	}
+}
+
+void skipMissedTicks() {
+	_G(last_tick_time) = AGS_Clock::now();
+	_G(next_frame_timestamp) = AGS_Clock::now();
+}
+
+} // namespace AGS3