Make emscripten work with draw limits

src/PowderToyFontEditor.cpp

@@ -82,7 +82,11 @@ int main(int argc, char * argv[])
 
 	while (engine.Running())
 	{
-		EngineProcess();
+		auto delay = EngineProcess();
+		if (delay.has_value())
+		{
+			SDL_Delay(std::max(*delay, UINT64_C(1)));
+		}
 	}
 	Platform::Exit(0);
 	return 0;

src/PowderToySDL.cpp

@@ -319,7 +319,7 @@ void SDLSetScreen()
 		SDL_SetWindowSize(sdl_window, size.X, size.Y);
 		LoadWindowPosition();
 	}
-	UpdateFpsLimit();
+	ApplyFpsLimit();
 	if (newFrameOpsNorm.fullscreen)
 	{
 		SDL_RaiseWindow(sdl_window);
@@ -450,7 +450,7 @@ static void EventProcess(const SDL_Event &event)
 	}
 }
 
-void EngineProcess()
+std::optional<uint64_t> EngineProcess()
 {
 	auto &engine = ui::Engine::Ref();
 	auto correctedFrameTime = tickSchedule.GetFrameTime();
@@ -509,8 +509,5 @@ void EngineProcess()
 			delay = tickSchedule.Arm(fpsLimitExplicit->value) / UINT64_C(1'000'000);
 		}
 	}
-	if (delay.has_value())
+	return delay;
-	{
-		SDL_Delay(std::max(*delay, UINT64_C(1)));
-	}
 }

src/PowderToySDL.h

@@ -6,6 +6,7 @@
 #include <cstdint>
 #include <SDL.h>
 #include <variant>
+#include <optional>
 
 extern int desktopWidth;
 extern int desktopHeight;
@@ -25,7 +26,7 @@ extern bool calculatedInitialMouse;
 extern bool hasMouseMoved;
 
 void MainLoop();
-void EngineProcess();
+std::optional<uint64_t> EngineProcess();
 void StartTextInput();
 void StopTextInput();
 void SetTextInputRect(int x, int y, int w, int h);
@@ -37,9 +38,8 @@ void blit(pixel *vid);
 void SDLOpen();
 void SDLClose();
 void SDLSetScreen();
-void SetFpsLimit(FpsLimit newFpsLimit);
 void LoadWindowPosition();
 void SaveWindowPosition();
 void LargeScreenDialog();
 void TickClient();
-void UpdateFpsLimit();
+void ApplyFpsLimit();

src/PowderToySDLCommon.cpp

@@ -5,14 +5,14 @@ void MainLoop()
 {
 	while (ui::Engine::Ref().Running())
 	{
-		EngineProcess();
+		auto delay = EngineProcess();
+		if (delay.has_value())
+		{
+			SDL_Delay(std::max(*delay, UINT64_C(1)));
+		}
 	}
 }
 
-void SetFpsLimit(FpsLimit newFpsLimit)
+void ApplyFpsLimit()
-{
-}
-
-void UpdateFpsLimit()
 {
 }

src/PowderToySDLEmscripten.cpp

@@ -14,7 +14,7 @@ static void MainLoopBody()
 	Platform::MaybeTriggerSyncFs();
 }
 
-void SetFpsLimit(FpsLimit newFpsLimit)
+void ApplyFpsLimit()
 {
 	static bool mainLoopSet = false;
 	if (!mainLoopSet)
@@ -22,31 +22,43 @@ void SetFpsLimit(FpsLimit newFpsLimit)
 		emscripten_set_main_loop(MainLoopBody, 0, 0);
 		mainLoopSet = true;
 	}
-	// if (std::get_if<FpsLimitVsync>(&newFpsLimit)) // TODO: DrawLimitVsync
+	// this generally attempts to replicate the behaviour of EngineProcess
+	std::optional<float> drawLimit;
+	auto &engine = ui::Engine::Ref();
+	auto fpsLimit = engine.GetFpsLimit();
+	if (auto *fpsLimitExplicit = std::get_if<FpsLimitExplicit>(&fpsLimit))
+	{
+		drawLimit = fpsLimitExplicit->value;
+	}
+	else if (std::holds_alternative<FpsLimitFollowDraw>(fpsLimit))
+	{
+		auto effectiveDrawLimit = engine.GetEffectiveDrawCap();
+		if (effectiveDrawLimit)
+		{
+			drawLimit = float(*effectiveDrawLimit);
+		}
+		// else // TODO: DrawLimitVsync
+		// {
+		// 	if (std::holds_alternative<DrawLimitVsync>(engine.GetDrawingFrequencyLimit()))
 		// 	{
 		// 		emscripten_set_main_loop_timing(EM_TIMING_RAF, 1);
 		// 		std::cerr << "implicit fps limit via vsync" << std::endl;
+		// 		return;
 		// 	}
-	// else
+		// }
-	// {
+	}
-		auto delay = 0;
+	int delay = 0; // no cap
-		if (auto *fpsLimitExplicit = std::get_if<FpsLimitExplicit>(&newFpsLimit))
+	if (drawLimit.has_value())
 	{
-			delay = int(1000.f / fpsLimitExplicit->value);
+		delay = int(1000.f / *drawLimit);
 	}
 	emscripten_set_main_loop_timing(EM_TIMING_SETTIMEOUT, delay);
 	std::cerr << "explicit fps limit: " << delay << "ms delays" << std::endl;
-	// }
-}
-
-void UpdateFpsLimit()
-{
-	SetFpsLimit(ui::Engine::Ref().GetFpsLimit());
 }
 
 // Is actually only called once at startup, the real main loop body is MainLoopBody.
 void MainLoop()
 {
-	UpdateFpsLimit();
+	ApplyFpsLimit();
 	MainLoopBody();
 }

src/gui/interface/Engine.cpp

@@ -39,7 +39,7 @@ Engine::~Engine()
 
 void Engine::ApplyFpsLimit()
 {
-	::SetFpsLimit(GetFpsLimit());
+	::ApplyFpsLimit();
 }
 
 void Engine::Begin()