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.

6 files changed, 55 insertions, 15 deletions

diff --git a/src/video/allegro_v.cpp b/src/video/allegro_v.cpp
index de329db9e..800cce40c 100644
--- a/src/video/allegro_v.cpp
+++ b/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);
+			}
 		}
 	}
 }
diff --git a/src/video/cocoa/cocoa_v.mm b/src/video/cocoa/cocoa_v.mm
index 20f3904ae..7c8981f61 100644
--- a/src/video/cocoa/cocoa_v.mm
+++ b/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);
+				}
 			}
 		}
 	}
diff --git a/src/video/dedicated_v.cpp b/src/video/dedicated_v.cpp
index 7b1abbadd..845b0bf8c 100644
--- a/src/video/dedicated_v.cpp
+++ b/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);
+				}
 			}
 		}
 	}
diff --git a/src/video/sdl2_v.cpp b/src/video/sdl2_v.cpp
index a8d8fc3e1..7c04b8743 100644
--- a/src/video/sdl2_v.cpp
+++ b/src/video/sdl2_v.cpp
@@ -824,10 +824,17 @@ 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) {
-		if (_draw_mutex != nullptr) draw_lock.unlock();
-		CSleep(1);
-		if (_draw_mutex != nullptr) draw_lock.lock();
+		/* 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();
+			std::this_thread::sleep_for(next_tick - now);
+			if (_draw_mutex != nullptr) draw_lock.lock();
+		}
 	}
 #endif
 }
diff --git a/src/video/sdl_v.cpp b/src/video/sdl_v.cpp
index 11da9c5a3..9f28b641c 100644
--- a/src/video/sdl_v.cpp
+++ b/src/video/sdl_v.cpp
@@ -782,10 +782,17 @@ 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) {
-			if (_draw_mutex != nullptr) draw_lock.unlock();
-			CSleep(1);
-			if (_draw_mutex != nullptr) draw_lock.lock();
+			/* 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();
+				std::this_thread::sleep_for(next_tick - now);
+				if (_draw_mutex != nullptr) draw_lock.lock();
+			}
 		}
 	}
 
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
index 2fe5f67f0..42fcf3f4b 100644
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -1258,13 +1258,20 @@ 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) {
-			/* Flush GDI buffer to ensure we don't conflict with the drawing thread. */
-			GdiFlush();
+			/* 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 (_draw_mutex != nullptr) draw_lock.unlock();
-			CSleep(1);
-			if (_draw_mutex != nullptr) draw_lock.lock();
+			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();
+				std::this_thread::sleep_for(next_tick - now);
+				if (_draw_mutex != nullptr) draw_lock.lock();
+			}
 		}
 	}