Outputs: Say the menus are on the device, instead of showing black

When no screen on the stack shows anything on an output (we're in the
menus), the background screen draws "Menus are on your device" there.
UI drawn to an output gets the primary's DPI scale, over the whole output.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Common/UI/ScreenManager.cpp

@@ -2,6 +2,8 @@
 #include "Common/System/System.h"
 #include "Common/Data/Collections/TinySet.h"
 #include "Common/UI/ScreenManager.h"
+#include "Common/UI/Context.h"
+#include "Common/Render/DrawBuffer.h"
 #include "Common/UI/Root.h"
 #include "Common/UI/View.h"
 #include "Common/UI/ScrollView.h"
@@ -278,7 +280,11 @@ ScreenRenderFlags ScreenManager::Render(std::function<void()> afterPreRender) {
 
 	afterPreRender();
 
-	// Secondary outputs. The topmost screen with something for one draws it, otherwise it's left cleared.
+	// Secondary outputs. The topmost screen with something for one draws it, then the background screen.
+	UIContext *ui = getUIContext();
+	if (!outputs_.empty()) {
+		ui->BeginFrame();
+	}
 	for (const Output &output : outputs_) {
 		Draw::Swapchain *swapchain = output.display.swapchain;
 		if (!swapchain) {
@@ -289,11 +295,26 @@ ScreenRenderFlags ScreenManager::Render(std::function<void()> afterPreRender) {
 		draw_->GetFramebufferDimensions(swapchain, &w, &h);
 		draw_->SetViewport(Draw::Viewport{0.0f, 0.0f, (float)w, (float)h, 0.0f, 1.0f});
 		draw_->SetScissorRect(0, 0, w, h);
+
+		// UI drawn there gets the primary's DPI scale, over the whole output.
+		const float dpWidth = w * g_display.dpi_scale_x;
+		const float dpHeight = h * g_display.dpi_scale_y;
+		const Bounds primaryBounds = ui->GetBounds();
+		ui->SetBounds(Bounds(0, 0, dpWidth, dpHeight));
+		ui->Draw()->PushDrawMatrix(ComputeOrthoMatrix(dpWidth, dpHeight, draw_->GetDeviceCaps().coordConvention));
+		bool drawn = false;
 		for (auto iter = stack_.rbegin(); iter != stack_.rend(); ++iter) {
 			if (iter->screen->renderOutput(output.display)) {
+				drawn = true;
 				break;
 			}
 		}
+		if (!drawn && backgroundScreen_) {
+			backgroundScreen_->renderOutput(output.display);
+		}
+		ui->Flush();
+		ui->Draw()->PopDrawMatrix();
+		ui->SetBounds(primaryBounds);
 	}
 
 	// Now, start the final render pass. This is now the ONLY place where binding the backbuffer is allowed.

UI/MiscScreens.cpp

@@ -97,6 +97,20 @@ void HandleCommonMessages(UIMessage message, const char *value, ScreenManager *m
 	}
 }
 
+// Nothing on the stack shows anything there, so we're in the menus.
+bool BackgroundScreen::renderOutput(const OutputDisplay &output) {
+	if (output.role != OutputRole::Game) {
+		return false;
+	}
+	UIContext &dc = *screenManager()->getUIContext();
+	auto di = GetI18NCategory(I18NCat::DIALOG);
+	const Bounds &bounds = dc.GetBounds();
+	dc.Begin();
+	dc.DrawText(di->T("Menus are on your device"), bounds.centerX(), bounds.centerY(), 0xFF505050, ALIGN_CENTER);
+	dc.Flush();
+	return true;
+}
+
 ScreenRenderFlags BackgroundScreen::render(ScreenRenderMode mode) {
 	UIContext *uiContext = screenManager()->getUIContext();
 

UI/MiscScreens.h

@@ -37,6 +37,7 @@ inline void NoOpVoidBool(bool) {}
 class BackgroundScreen : public UIScreen {
 public:
 	ScreenRenderFlags render(ScreenRenderMode mode) override;
+	bool renderOutput(const OutputDisplay &output) override;
 	void sendMessage(UIMessage message, const char *value) override;
 
 private: