Clear depth buffers after changing depth rounding mode.

And thus change of depth buffer scale/offset.

Previously, old depth buffers with values that now are out of range
could stick around, causing #16941. This clears them to the expected 0
value, which helps Outrun. Ideally we should convert depth buffers to
the new format, but if we can get away without that, that's also nice.

This is enough for #16941.

GPU/Common/FramebufferManagerCommon.cpp

@@ -1059,7 +1059,14 @@ void FramebufferManagerCommon::NotifyRenderFramebufferSwitched(VirtualFramebuffe
 	if (useBufferedRendering_) {
 		if (vfb->fbo) {
 			shaderManager_->DirtyLastShader();
-			draw_->BindFramebufferAsRenderTarget(vfb->fbo, {Draw::RPAction::KEEP, Draw::RPAction::KEEP, Draw::RPAction::KEEP}, "FBSwitch");
+			Draw::RPAction depthAction = Draw::RPAction::KEEP;
+			float clearDepth = 0.0f;
+			if (vfb->usageFlags & FB_USAGE_INVALIDATE_DEPTH) {
+				depthAction = Draw::RPAction::CLEAR;
+				clearDepth = GetDepthScaleFactors().offset;
+				vfb->usageFlags &= ~FB_USAGE_INVALIDATE_DEPTH;
+			}
+			draw_->BindFramebufferAsRenderTarget(vfb->fbo, {Draw::RPAction::KEEP, depthAction, Draw::RPAction::KEEP, 0, clearDepth}, "FBSwitch");
 		} else {
 			// This should only happen very briefly when toggling useBufferedRendering_.
 			ResizeFramebufFBO(vfb, vfb->width, vfb->height, true);
@@ -2573,6 +2580,12 @@ void FramebufferManagerCommon::ShowScreenResolution() {
 	INFO_LOG(SYSTEM, "%s", messageStream.str().c_str());
 }
 
+void FramebufferManagerCommon::ClearAllDepthBuffers() {
+	for (auto vfb : vfbs_) {
+		vfb->usageFlags |= FB_USAGE_INVALIDATE_DEPTH;
+	}
+}
+
 // We might also want to implement an asynchronous callback-style version of this. Would probably
 // only be possible to implement optimally on Vulkan, but on GL and D3D11 we could do pixel buffers
 // and read on the next frame, then call the callback.

GPU/Common/FramebufferManagerCommon.h

@@ -46,6 +46,7 @@ enum {
 	FB_USAGE_FIRST_FRAME_SAVED = 128,
 	FB_USAGE_RENDER_DEPTH = 256,
 	FB_USAGE_COLOR_MIXED_DEPTH = 512,
+	FB_USAGE_INVALIDATE_DEPTH = 1024,  // used to clear depth buffers.
 };
 
 enum {
@@ -317,6 +318,10 @@ class FramebufferManagerCommon {
 	void ApplyClearToMemory(int x1, int y1, int x2, int y2, u32 clearColor);
 	bool PerformWriteStencilFromMemory(u32 addr, int size, WriteStencil flags);
 
+	// We changed our depth mode, gotta start over.
+	// Ideally, we should convert depth buffers here, not just clear them.
+	void ClearAllDepthBuffers();
+
 	// Returns true if it's sure this is a direct FBO->FBO transfer and it has already handle it.
 	// In that case we hardly need to actually copy the bytes in VRAM, they will be wrong anyway (unless
 	// read framebuffers is on, in which case this should always return false).

GPU/D3D11/GPU_D3D11.cpp

@@ -161,8 +161,9 @@ void GPU_D3D11::BeginFrame() {
 	if (gstate_c.useFlagsChanged) {
 		// TODO: It'd be better to recompile them in the background, probably?
 		// This most likely means that saw equal depth changed.
-		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders");
+		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders and depth buffers");
 		shaderManagerD3D11_->ClearShaders();
+		framebufferManager_->ClearAllDepthBuffers();
 		drawEngine_.ClearInputLayoutMap();
 		gstate_c.useFlagsChanged = false;
 	}

GPU/Directx9/GPU_DX9.cpp

@@ -159,8 +159,9 @@ void GPU_DX9::BeginFrame() {
 	if (gstate_c.useFlagsChanged) {
 		// TODO: It'd be better to recompile them in the background, probably?
 		// This most likely means that saw equal depth changed.
-		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders");
+		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders and depth buffers");
 		shaderManagerDX9_->ClearCache(true);
+		framebufferManager_->ClearAllDepthBuffers();
 		gstate_c.useFlagsChanged = false;
 	}
 }

GPU/GLES/GPU_GLES.cpp

@@ -283,8 +283,9 @@ void GPU_GLES::BeginHostFrame() {
 	if (gstate_c.useFlagsChanged) {
 		// TODO: It'd be better to recompile them in the background, probably?
 		// This most likely means that saw equal depth changed.
-		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders");
+		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders and depth buffers");
 		shaderManagerGL_->ClearCache(true);
+		framebufferManager_->ClearAllDepthBuffers();
 		gstate_c.useFlagsChanged = false;
 	}
 }

GPU/Vulkan/GPU_Vulkan.cpp

@@ -310,9 +310,12 @@ void GPU_Vulkan::BeginHostFrame() {
 	if (gstate_c.useFlagsChanged) {
 		// TODO: It'd be better to recompile them in the background, probably?
 		// This most likely means that saw equal depth changed.
-		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders");
+		WARN_LOG(G3D, "Shader use flags changed, clearing all shaders and depth buffers");
+		// TODO: Not all shaders need to be recompiled. In fact, quite few? Of course, depends on
+		// the use flag change.. This is a major frame rate hitch in the start of a race in Outrun.
 		shaderManagerVulkan_->ClearShaders();
 		pipelineManager_->Clear();
+		framebufferManager_->ClearAllDepthBuffers();
 		gstate_c.useFlagsChanged = false;
 	}