Don't discard the backbuffer depth/stencil in setCanvas.

#1893.

src/modules/graphics/metal/Graphics.h

@@ -207,7 +207,7 @@ private:
 	void initCapabilities() override;
 	void getAPIStats(int &shaderswitches) const override;
 
-	void endPass();
+	void endPass(bool presenting);
 
 	id<MTLDepthStencilState> getCachedDepthStencilState(const DepthState &depth, const StencilState &stencil);
 	void applyRenderState(id<MTLRenderCommandEncoder> renderEncoder, const VertexAttributes &attributes);

src/modules/graphics/metal/Graphics.mm

@@ -1358,7 +1358,7 @@ bool Graphics::dispatch(int x, int y, int z)
 
 void Graphics::setRenderTargetsInternal(const RenderTargets &rts, int /*pixelw*/, int /*pixelh*/, bool /*hasSRGBtexture*/)
 { @autoreleasepool {
-	endPass();
+	endPass(false);
 
 	bool isbackbuffer = rts.getFirstTarget().texture == nullptr;
 
@@ -1410,7 +1410,7 @@ void Graphics::setRenderTargetsInternal(const RenderTargets &rts, int /*pixelw*/
 	dirtyRenderState = STATEBIT_ALL;
 }}
 
-void Graphics::endPass()
+void Graphics::endPass(bool presenting)
 {
 	// Make sure the encoder gets set up, if nothing else has done it yet.
 	useRenderEncoder();
@@ -1421,9 +1421,9 @@ void Graphics::endPass()
 	love::graphics::Texture *depthstencil = rts.depthStencil.texture.get();
 
 	// Discard the depth/stencil buffer if we're using an internal cached one,
-	// or if this is the backbuffer.
+	// or if we're presenting the backbuffer to the display.
 	if ((depthstencil == nullptr && (rts.temporaryRTFlags & (TEMPORARY_RT_DEPTH | TEMPORARY_RT_STENCIL)) != 0)
-		|| !rts.getFirstTarget().texture.get())
+		|| (presenting && !rts.getFirstTarget().texture.get()))
 	{
 		attachmentStoreActions.depth = MTLStoreActionDontCare;
 		attachmentStoreActions.stencil = MTLStoreActionDontCare;
@@ -1562,7 +1562,7 @@ void Graphics::present(void *screenshotCallbackData)
 
 	// endPass calls useRenderEncoder, which makes sure activeDrawable is set
 	// when possible.
-	endPass();
+	endPass(true);
 
 	id<MTLBuffer> screenshotbuffer = nil;
 

src/modules/graphics/opengl/Graphics.cpp

@@ -758,7 +758,7 @@ void Graphics::setRenderTargetsInternal(const RenderTargets &rts, int pixelw, in
 
 	OpenGL::TempDebugGroup debuggroup("setRenderTargets");
 
-	endPass();
+	endPass(false);
 
 	bool iswindow = rts.getFirstTarget().texture == nullptr;
 	Winding vertexwinding = state.winding;
@@ -794,16 +794,18 @@ void Graphics::setRenderTargetsInternal(const RenderTargets &rts, int pixelw, in
 	}
 }
 
-void Graphics::endPass()
+void Graphics::endPass(bool presenting)
 {
 	auto &rts = states.back().renderTargets;
 	love::graphics::Texture *depthstencil = rts.depthStencil.texture.get();
 
-	// Discard the depth/stencil buffer if we're using an internal cached one.
-	if (depthstencil == nullptr && (rts.temporaryRTFlags & (TEMPORARY_RT_DEPTH | TEMPORARY_RT_STENCIL)) != 0)
+	// Discard the depth/stencil buffer if we're using an internal cached one,
+	// or if we're presenting the backbuffer to the display.
+	if ((depthstencil == nullptr && (rts.temporaryRTFlags & (TEMPORARY_RT_DEPTH | TEMPORARY_RT_STENCIL)) != 0)
+		|| (presenting && !rts.getFirstTarget().texture.get()))
+	{
 		discard({}, true);
-	else if (!rts.getFirstTarget().texture.get())
-		discard({}, true); // Backbuffer
+	}
 
 	// Resolve MSAA buffers. MSAA is only supported for 2D render targets so we
 	// don't have to worry about resolving to slices.
@@ -1224,7 +1226,8 @@ void Graphics::present(void *screenshotCallbackData)
 	deprecations.draw(this);
 
 	flushBatchedDraws();
-	endPass();
+
+	endPass(true);
 
 	int w = getPixelWidth();
 	int h = getPixelHeight();

src/modules/graphics/opengl/Graphics.h

@@ -149,7 +149,7 @@ private:
 	void initCapabilities() override;
 	void getAPIStats(int &shaderswitches) const override;
 
-	void endPass();
+	void endPass(bool presenting);
 	GLuint bindCachedFBO(const RenderTargets &targets);
 	void discard(OpenGL::FramebufferTarget target, const std::vector<bool> &colorbuffers, bool depthstencil);