Change approach somewhat to avoid adding drawing code in the screen manager.

UI/DevScreens.cpp

@@ -815,7 +815,7 @@ void ShaderListScreen::CreateViews() {
 	layout->Add(tabs_);
 	layout->Add(new Button(di->T("Back")))->OnClick.Handle<UIScreen>(this, &UIScreen::OnBack);
 
-	for (int i = 0; i < ARRAY_SIZE(shaderTypes); i++) {
+	for (size_t i = 0; i < ARRAY_SIZE(shaderTypes); i++) {
 		ScrollView *scroll = new ScrollView(ORIENT_VERTICAL, new LinearLayoutParams(1.0));
 		LinearLayout *shaderList = new LinearLayout(ORIENT_VERTICAL, new LayoutParams(FILL_PARENT, WRAP_CONTENT));
 		ListShaders(shaderTypes[i].type, shaderList);

UI/EmuScreen.cpp

@@ -861,6 +861,24 @@ void EmuScreen::render() {
 		}
 	}
 
+	bool useBufferedRendering = g_Config.iRenderingMode != FB_NON_BUFFERED_MODE;
+
+	if (!useBufferedRendering) {
+		Thin3DContext *thin3d = screenManager()->getThin3DContext();
+		thin3d->Clear(T3DClear::COLOR | T3DClear::DEPTH | T3DClear::STENCIL, 0xFF000000, 0.0f, 0);
+
+		T3DViewport viewport;
+		viewport.TopLeftX = 0;
+		viewport.TopLeftY = 0;
+		viewport.Width = pixel_xres;
+		viewport.Height = pixel_yres;
+		viewport.MaxDepth = 1.0;
+		viewport.MinDepth = 0.0;
+		thin3d->SetViewports(1, &viewport);
+		thin3d->SetTargetSize(pixel_xres, pixel_yres);
+	}
+
+
 	// Reapply the graphics state of the PSP
 	ReapplyGfxState();
 
@@ -882,7 +900,6 @@ void EmuScreen::render() {
 	if (invalid_)
 		return;
 
-	bool useBufferedRendering = g_Config.iRenderingMode != FB_NON_BUFFERED_MODE;
 	if (useBufferedRendering && g_Config.iGPUBackend == GPU_BACKEND_OPENGL)
 		fbo_unbind();
 
@@ -970,9 +987,3 @@ void EmuScreen::releaseButtons() {
 	input.id = 0;
 	touch(input);
 }
-
-int EmuScreen::expects() const {
-	// We only want the framework to clear for us when we are running non-buffered. Otherwise, it's a complete waste of time
-	// to clear the backbuffer only to then go off rendering to another buffer. Better to clear when we are actually copying the final image instead.
-	return (g_Config.iRenderingMode == FB_NON_BUFFERED_MODE) ? (SCREEN_EXPECTS_CLEAR | SCREEN_EXPECTS_VIEWPORT) : 0;
-}

UI/EmuScreen.h

@@ -45,8 +45,6 @@ public:
 	bool key(const KeyInput &key) override;
 	bool axis(const AxisInput &axis) override;
 
-	int expects() const override;
-
 protected:
 	void CreateViews() override;
 	UI::EventReturn OnDevTools(UI::EventParams &params);

ext/native/ui/screen.cpp

@@ -99,24 +99,6 @@ void ScreenManager::resized() {
 
 void ScreenManager::render() {
 	if (!stack_.empty()) {
-		int expects = stack_.back().screen->expects();
-
-		if (expects & SCREEN_EXPECTS_CLEAR) {
-			thin3DContext_->Clear(T3DClear::COLOR | T3DClear::DEPTH | T3DClear::STENCIL, 0xFF000000, 0.0f, 0);
-		}
-
-		if (expects & SCREEN_EXPECTS_VIEWPORT) {
-			T3DViewport viewport;
-			viewport.TopLeftX = 0;
-			viewport.TopLeftY = 0;
-			viewport.Width = pixel_xres;
-			viewport.Height = pixel_yres;
-			viewport.MaxDepth = 1.0;
-			viewport.MinDepth = 0.0;
-			thin3DContext_->SetViewports(1, &viewport);
-			thin3DContext_->SetTargetSize(pixel_xres, pixel_yres);
-		}
-
 		switch (stack_.back().flags) {
 		case LAYER_SIDEMENU:
 		case LAYER_TRANSPARENT:
@@ -128,13 +110,19 @@ void ScreenManager::render() {
 				iter--;
 				iter--;
 				Layer backback = *iter;
-				// Also shift to the right somehow...
+
+				// TODO: Make really sure that this "mismatched" pre/post only happens
+				// when screens are "compatible" (both are UIScreens, for example).
+				backback.screen->preRender();
 				backback.screen->render();
 				stack_.back().screen->render();
+				stack_.back().screen->postRender();
 				break;
 			}
 		default:
+			stack_.back().screen->preRender();
 			stack_.back().screen->render();
+			stack_.back().screen->postRender();
 			break;
 		}
 	} else {

ext/native/ui/screen.h

@@ -33,12 +33,6 @@ enum DialogResult {
 	DR_BACK,
 };
 
-
-enum {
-	SCREEN_EXPECTS_VIEWPORT = 1 << 0,
-	SCREEN_EXPECTS_CLEAR = 1 << 1,
-};
-
 class ScreenManager;
 class UIContext;
 class Thin3DContext;
@@ -52,7 +46,9 @@ public:
 
 	virtual void onFinish(DialogResult reason) {}
 	virtual void update(InputState &input) {}
+	virtual void preRender() {}
 	virtual void render() {}
+	virtual void postRender() {}
 	virtual void deviceLost() {}
 	virtual void resized() {}
 	virtual void dialogFinished(const Screen *dialog, DialogResult result) {}
@@ -75,8 +71,6 @@ public:
 	virtual bool isTransparent() const { return false; }
 	virtual bool isTopLevel() const { return false; }
 
-	virtual int expects() const { return SCREEN_EXPECTS_VIEWPORT | SCREEN_EXPECTS_CLEAR; }
-
 private:
 	ScreenManager *screenManager_;
 	DISALLOW_COPY_AND_ASSIGN(Screen);

ext/native/ui/ui_screen.cpp

@@ -1,3 +1,4 @@
+#include "base/display.h"
 #include "input/input_state.h"
 #include "input/keycodes.h"
 #include "ui/ui_screen.h"
@@ -36,6 +37,24 @@ void UIScreen::update(InputState &input) {
 	}
 }
 
+void UIScreen::preRender() {
+	Thin3DContext *thin3d = screenManager()->getThin3DContext();
+	thin3d->Clear(T3DClear::COLOR | T3DClear::DEPTH | T3DClear::STENCIL, 0xFF000000, 0.0f, 0);
+
+	T3DViewport viewport;
+	viewport.TopLeftX = 0;
+	viewport.TopLeftY = 0;
+	viewport.Width = pixel_xres;
+	viewport.Height = pixel_yres;
+	viewport.MaxDepth = 1.0;
+	viewport.MinDepth = 0.0;
+	thin3d->SetViewports(1, &viewport);
+	thin3d->SetTargetSize(pixel_xres, pixel_yres);
+}
+
+void UIScreen::postRender() {
+}
+
 void UIScreen::render() {
 	DoRecreateViews();
 

ext/native/ui/ui_screen.h

@@ -12,7 +12,9 @@ public:
 	~UIScreen();
 
 	virtual void update(InputState &input) override;
+	virtual void preRender() override;
 	virtual void render() override;
+	virtual void postRender() override;
 
 	virtual bool touch(const TouchInput &touch) override;
 	virtual bool key(const KeyInput &touch) override;