Add option to improve frame pacing through duplicate frames if framerate is below 60hz.

Should help #9736, and fixes #12325.

Author: hrydgard

Core/Config.cpp

@@ -776,6 +776,7 @@ static ConfigSetting graphicsSettings[] = {
 	ConfigSetting("LogFrameDrops", &g_Config.bLogFrameDrops, false, true, false),
 
 	ConfigSetting("InflightFrames", &g_Config.iInflightFrames, 3, true, false),
+	ConfigSetting("RenderDuplicateFrames", &g_Config.bRenderDuplicateFrames, false, true, true),
 
 	ConfigSetting(false),
 };

Core/Config.h

@@ -207,6 +207,7 @@ struct Config {
 	bool bGfxDebugOutput;
 	bool bGfxDebugSplitSubmit;
 	int iInflightFrames;
+	bool bRenderDuplicateFrames;
 
 	// Sound
 	bool bEnableSound;

Core/HLE/sceDisplay.cpp

@@ -753,9 +753,11 @@ void __DisplayFlip(int cyclesLate) {
 	// Also let's always flip for animated shaders.
 	const ShaderInfo *shaderInfo = g_Config.sPostShaderName == "Off" ? nullptr : GetPostShaderInfo(g_Config.sPostShaderName);
 	bool postEffectRequiresFlip = false;
+	// postEffectRequiresFlip is not compatible with frameskip unthrottling, see #12325.
 	if (shaderInfo && g_Config.iRenderingMode != FB_NON_BUFFERED_MODE)
-		postEffectRequiresFlip = shaderInfo->requires60fps;
+		postEffectRequiresFlip = (shaderInfo->requires60fps || g_Config.bRenderDuplicateFrames) && !(g_Config.bFrameSkipUnthrottle && !FrameTimingThrottled());
 	const bool fbDirty = gpu->FramebufferDirty();
+
 	if (fbDirty || noRecentFlip || postEffectRequiresFlip) {
 		int frameSleepPos = frameTimeHistoryPos;
 		CalculateFPS();

UI/GameSettingsScreen.cpp

@@ -343,6 +343,11 @@ void GameSettingsScreen::CreateViews() {
 		return UI::EVENT_CONTINUE;
 	});
 #endif
+	CheckBox *frameDuplication = graphicsSettings->Add(new CheckBox(&g_Config.bRenderDuplicateFrames, gr->T("Render duplicate frames to 60hz")));
+	frameDuplication->OnClick.Add([=](EventParams &e) {
+		settingInfo_->Show(gr->T("RenderDuplicateFrames Tip", "Can make framerate smoother in games that run at lower framerates"), e.v);
+		return UI::EVENT_CONTINUE;
+	});
 
 	if (GetGPUBackend() == GPUBackend::VULKAN || GetGPUBackend() == GPUBackend::OPENGL) {
 		static const char *bufferOptions[] = { "No buffer", "Up to 1", "Up to 2" };