Change: sleep till the next tick in the main loop

Sleep for 1ms (which is always (a lot) more than 1ms) is just
randomly guessing and hoping you hit your deadline, give or take.

But given we can calculate when our next frame is happening, we
can just sleep for that exact amount. As these values are often
a bit larger, it is also more likely the OS can schedule us back
in close to our requested target. This means it is more likely we
hit our deadlines, which makes the FPS a lot more stable.

src/video/allegro_v.cpp

@@ -521,8 +521,15 @@ void VideoDriver_Allegro::MainLoop()
 			DrawSurfaceToScreen();
 		}
 
+		/* If we are not in fast-forward, create some time between calls to ease up CPU usage. */
 		if (!_fast_forward || _pause_mode) {
-			CSleep(1);
+			/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+			auto next_tick = std::min(next_draw_tick, next_game_tick);
+			auto now = std::chrono::steady_clock::now();
+
+			if (next_tick > now) {
+				std::this_thread::sleep_for(next_tick - now);
+			}
 		}
 	}
 }

src/video/cocoa/cocoa_v.mm

@@ -704,8 +704,15 @@ void VideoDriver_Cocoa::GameLoop()
 				this->Draw();
 			}
 
+			/* If we are not in fast-forward, create some time between calls to ease up CPU usage. */
 			if (!_fast_forward || _pause_mode) {
-				CSleep(1);
+				/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+				auto next_tick = std::min(next_draw_tick, next_game_tick);
+				auto now = std::chrono::steady_clock::now();
+
+				if (next_tick > now) {
+					std::this_thread::sleep_for(next_tick - now);
+				}
 			}
 		}
 	}

src/video/dedicated_v.cpp

@@ -311,9 +311,14 @@ void VideoDriver_Dedicated::MainLoop()
 			/* Sleep longer on a dedicated server, if the game is paused and no clients connected.
 			 * That can allow the CPU to better use deep sleep states. */
 			if (_pause_mode != 0 && !HasClients()) {
-				CSleep(100);
+				std::this_thread::sleep_for(std::chrono::milliseconds(100));
 			} else {
-				CSleep(1);
+				/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+				auto now = std::chrono::steady_clock::now();
+
+				if (next_game_tick > now) {
+					std::this_thread::sleep_for(next_game_tick - now);
+				}
 			}
 		}
 	}

src/video/sdl2_v.cpp

@@ -824,11 +824,18 @@ void VideoDriver_SDL::LoopOnce()
 /* Emscripten is running an event-based mainloop; there is already some
  * downtime between each iteration, so no need to sleep. */
 #ifndef __EMSCRIPTEN__
+	/* If we are not in fast-forward, create some time between calls to ease up CPU usage. */
 	if (!_fast_forward || _pause_mode) {
+		/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+		auto next_tick = std::min(next_draw_tick, next_game_tick);
+		auto now = std::chrono::steady_clock::now();
+
+		if (next_tick > now) {
 			if (_draw_mutex != nullptr) draw_lock.unlock();
-		CSleep(1);
+			std::this_thread::sleep_for(next_tick - now);
 			if (_draw_mutex != nullptr) draw_lock.lock();
 		}
+	}
 #endif
 }
 

src/video/sdl_v.cpp

@@ -782,12 +782,19 @@ void VideoDriver_SDL::MainLoop()
 			}
 		}
 
+		/* If we are not in fast-forward, create some time between calls to ease up CPU usage. */
 		if (!_fast_forward || _pause_mode) {
+			/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+			auto next_tick = std::min(next_draw_tick, next_game_tick);
+			auto now = std::chrono::steady_clock::now();
+
+			if (next_tick > now) {
 				if (_draw_mutex != nullptr) draw_lock.unlock();
-			CSleep(1);
+				std::this_thread::sleep_for(next_tick - now);
 				if (_draw_mutex != nullptr) draw_lock.lock();
 			}
 		}
+	}
 
 	if (_draw_mutex != nullptr) {
 		_draw_continue = false;

src/video/win32_v.cpp

@@ -1258,15 +1258,22 @@ void VideoDriver_Win32::MainLoop()
 			CheckPaletteAnim();
 		}
 
+		/* If we are not in fast-forward, create some time between calls to ease up CPU usage. */
 		if (!_fast_forward || _pause_mode) {
+			/* See how much time there is till we have to process the next event, and try to hit that as close as possible. */
+			auto next_tick = std::min(next_draw_tick, next_game_tick);
+			auto now = std::chrono::steady_clock::now();
+
+			if (next_tick > now) {
 				/* Flush GDI buffer to ensure we don't conflict with the drawing thread. */
 				GdiFlush();
 
 				if (_draw_mutex != nullptr) draw_lock.unlock();
-			CSleep(1);
+				std::this_thread::sleep_for(next_tick - now);
 				if (_draw_mutex != nullptr) draw_lock.lock();
 			}
 		}
+	}
 
 	if (_draw_threaded) {
 		_draw_continue = false;