Force postshaders with the usePreviousFrame flag to the end of the order

GPU/Common/PostShader.cpp

@@ -324,3 +324,25 @@ const TextureShaderInfo *GetTextureShaderInfo(const std::string &name) {
 const std::vector<TextureShaderInfo> &GetAllTextureShaderInfo() {
 	return textureShaderInfo;
 }
+
+void FixPostShaderOrder(std::vector<std::string> *names) {
+	// There's one rule only that we enforce - only one shader can use UsePreviousFrame,
+	// and it has to be the last one. So we simply remove any we find from the list,
+	// and then append it to the end if there is one.
+	std::string prevFrameShader;
+	for (auto iter = names->begin(); iter != names->end(); ) {
+		const ShaderInfo *info = GetPostShaderInfo(*iter);
+		if (info) {
+			if (info->usePreviousFrame) {
+				prevFrameShader = *iter;
+				iter = names->erase(iter++);
+				continue;
+			}
+		}
+		++iter;
+	}
+
+	if (!prevFrameShader.empty()) {
+		names->push_back(prevFrameShader);
+	}
+}

GPU/Common/PostShader.h

@@ -115,3 +115,8 @@ const std::vector<ShaderInfo> &GetAllPostShaderInfo();
 const TextureShaderInfo *GetTextureShaderInfo(const std::string &name);
 const std::vector<TextureShaderInfo> &GetAllTextureShaderInfo();
 void RemoveUnknownPostShaders(std::vector<std::string> *names);
+
+// Call this any time you alter the postshader list. It makes sure
+// that "usePrevFrame" shaders are at the end, and that there's only one.
+// It'll also enforce any similar future rules.
+void FixPostShaderOrder(std::vector<std::string> *names);

GPU/Common/PresentationCommon.cpp

@@ -880,6 +880,7 @@ void PresentationCommon::CalculateRenderResolution(int *width, int *height, int
 	if (!g_Config.vPostShaderNames.empty()) {
 		ReloadAllPostShaderInfo(draw_);
 		RemoveUnknownPostShaders(&g_Config.vPostShaderNames);
+		FixPostShaderOrder(&g_Config.vPostShaderNames);
 		shaderInfo = GetFullPostShadersChain(g_Config.vPostShaderNames);
 	}
 

UI/DisplayLayoutScreen.cpp

@@ -152,6 +152,7 @@ void DisplayLayoutScreen::dialogFinished(const Screen *dialog, DialogResult resu
 UI::EventReturn DisplayLayoutScreen::OnPostProcShaderChange(UI::EventParams &e) {
 	// Remove the virtual "Off" entry. TODO: Get rid of it generally.
 	g_Config.vPostShaderNames.erase(std::remove(g_Config.vPostShaderNames.begin(), g_Config.vPostShaderNames.end(), "Off"), g_Config.vPostShaderNames.end());
+	FixPostShaderOrder(&g_Config.vPostShaderNames);
 
 	NativeMessageReceived("gpu_configChanged", "");
 	NativeMessageReceived("gpu_renderResized", "");  // To deal with shaders that can change render resolution like upscaling.
@@ -370,7 +371,9 @@ void DisplayLayoutScreen::CreateViews() {
 			moreButton->OnClick.Add([=](EventParams &e) -> UI::EventReturn {
 				PopupContextMenuScreen *contextMenu = new UI::PopupContextMenuScreen(postShaderContextMenu, ARRAY_SIZE(postShaderContextMenu), di.get(), moreButton);
 				screenManager()->push(contextMenu);
-				contextMenu->SetEnabled(0, i > 0);
+				const ShaderInfo *info = GetPostShaderInfo(g_Config.vPostShaderNames[i]);
+				bool usesLastFrame = info ? info->usePreviousFrame : false;
+				contextMenu->SetEnabled(0, i > 0 && !usesLastFrame);
 				contextMenu->SetEnabled(1, i < g_Config.vPostShaderNames.size() - 1);
 				contextMenu->OnChoice.Add([=](EventParams &e) -> UI::EventReturn {
 					switch (e.a) {
@@ -386,6 +389,7 @@ void DisplayLayoutScreen::CreateViews() {
 					default:
 						return UI::EVENT_DONE;
 					}
+					FixPostShaderOrder(&g_Config.vPostShaderNames);
 					NativeMessageReceived("gpu_configChanged", "");
 					RecreateViews();
 					return UI::EVENT_DONE;