Additional semaphore to synchronize offscreen and final render (Refs #70)

offscreen/offscreen.cpp

@@ -119,12 +119,17 @@ public:
 
 	VkCommandBuffer offScreenCmdBuffer = VK_NULL_HANDLE;
 
+	// Semaphore used to synchronize between offscreen and final scene rendering
+	VkSemaphore offscreenSemaphore = VK_NULL_HANDLE;
+
 	glm::vec3 meshPos = glm::vec3(0.0f, -1.5f, 0.0f);
+	glm::vec3 meshRot = glm::vec3(0.0f);
 
 	VulkanExample() : VulkanExampleBase(ENABLE_VALIDATION)
 	{
-		zoom = -6.5f;
-		rotation = { -11.25f, 45.0f, 0.0f };
+		zoom = -6.0f;
+		rotation = { -2.5f, 0.0f, 0.0f };
+		cameraPos = { 0.0f, 1.0f, 0.0f };
 		timerSpeed *= 0.25f;
 		enableTextOverlay = true;
 		title = "Vulkan Example - Offscreen rendering";
@@ -176,6 +181,7 @@ public:
 		vkTools::destroyUniformData(device, &uniformData.vsDebugQuad);
 
 		vkFreeCommandBuffers(device, cmdPool, 1, &offScreenCmdBuffer);
+		vkDestroySemaphore(device, offscreenSemaphore, nullptr);
 	}
 
 	// Preapre an empty texture as the blit target from 
@@ -374,21 +380,18 @@ public:
 		VK_CHECK_RESULT(vkCreateFramebuffer(device, &fbufCreateInfo, nullptr, &offScreenFrameBuf.frameBuffer));
 	}
 
-	void createOffscreenCommandBuffer()
-	{
-		VkCommandBufferAllocateInfo cmd = vkTools::initializers::commandBufferAllocateInfo(
-			cmdPool,
-			VK_COMMAND_BUFFER_LEVEL_PRIMARY,
-			1);
-		VK_CHECK_RESULT(vkAllocateCommandBuffers(device, &cmd, &offScreenCmdBuffer));
-	}
-
-	// The command buffer to copy for rendering 
-	// the offscreen scene and blitting it into
-	// the texture target is only build once
-	// and gets resubmitted 
+	// Sets up the command buffer that renders the scene to the offscreen frame buffer
 	void buildOffscreenCommandBuffer()
 	{
+		if (offScreenCmdBuffer == VK_NULL_HANDLE)
+		{
+			offScreenCmdBuffer = VulkanExampleBase::createCommandBuffer(VK_COMMAND_BUFFER_LEVEL_PRIMARY, false);
+		}
+
+		// Create a semaphore used to synchronize offscreen rendering and usage
+		VkSemaphoreCreateInfo semaphoreCreateInfo = vkTools::initializers::semaphoreCreateInfo();
+		VK_CHECK_RESULT(vkCreateSemaphore(device, &semaphoreCreateInfo, nullptr, &offscreenSemaphore));
+
 		VkCommandBufferBeginInfo cmdBufInfo = vkTools::initializers::commandBufferBeginInfo();
 
 		VkClearValue clearValues[2];
@@ -983,7 +986,7 @@ public:
 
 		ubos.vsShared.model = viewMatrix * glm::translate(glm::mat4(), cameraPos);
 		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.x), glm::vec3(1.0f, 0.0f, 0.0f));
-		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.y), glm::vec3(0.0f, 1.0f, 0.0f));
+		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.y + meshRot.y), glm::vec3(0.0f, 1.0f, 0.0f));
 		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.z), glm::vec3(0.0f, 0.0f, 1.0f));
 
 		ubos.vsShared.model = glm::translate(ubos.vsShared.model, meshPos);
@@ -1019,7 +1022,7 @@ public:
 
 		ubos.vsShared.model = viewMatrix * glm::translate(glm::mat4(), cameraPos);
 		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.x), glm::vec3(1.0f, 0.0f, 0.0f));
-		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.y), glm::vec3(0.0f, 1.0f, 0.0f));
+		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.y + meshRot.y), glm::vec3(0.0f, 1.0f, 0.0f));
 		ubos.vsShared.model = glm::rotate(ubos.vsShared.model, glm::radians(rotation.z), glm::vec3(0.0f, 0.0f, 1.0f));
 
 		ubos.vsShared.model = glm::scale(ubos.vsShared.model, glm::vec3(1.0f, -1.0f, 1.0f));
@@ -1035,16 +1038,38 @@ public:
 	{
 		VulkanExampleBase::prepareFrame();
 
-		// Submit offscreen rendering command buffer 
-		// todo : use event to ensure that offscreen result is finished bfore render command buffer is started
-		std::vector<VkCommandBuffer> submitCmdBuffers = {
-			offScreenCmdBuffer,
-			drawCmdBuffers[currentBuffer],
-		};
-		submitCmdBuffers.push_back(drawCmdBuffers[currentBuffer]);
-		submitInfo.commandBufferCount = submitCmdBuffers.size();
-		submitInfo.pCommandBuffers = submitCmdBuffers.data();
+		// The scene render command buffer has to wait for the offscreen
+		// rendering to be finished before we can use the framebuffer 
+		// color image for sampling during final rendering
+		// To ensure this we use a dedicated offscreen synchronization
+		// semaphore that will be signaled when offscreen renderin
+		// has been finished
+		// This is necessary as an implementation may start both
+		// command buffers at the same time, there is no guarantee
+		// that commnad buffers will be executed in the order they
+		// have been submitted by the application
 
+		// Offscreen rendering
+
+		// Wait for swap chain presentation to finish
+		submitInfo.pWaitSemaphores = &semaphores.presentComplete;
+		// Signal ready with offscreen semaphore
+		submitInfo.pSignalSemaphores = &offscreenSemaphore;
+
+		// Submit work
+		submitInfo.commandBufferCount = 1;
+		submitInfo.pCommandBuffers = &offScreenCmdBuffer;
+		VK_CHECK_RESULT(vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE));
+
+		// Scene rendering
+
+		// Wait for offscreen semaphore
+		submitInfo.pWaitSemaphores = &offscreenSemaphore;
+		// Signal ready with render complete semaphpre
+		submitInfo.pSignalSemaphores = &semaphores.renderComplete;
+
+		// Submit work
+		submitInfo.pCommandBuffers = &drawCmdBuffers[currentBuffer];
 		VK_CHECK_RESULT(vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE));
 
 		VulkanExampleBase::submitFrame();
@@ -1063,7 +1088,6 @@ public:
 		preparePipelines();
 		setupDescriptorPool();
 		setupDescriptorSet();
-		createOffscreenCommandBuffer();
 		prepareOffscreenFramebuffer();
 		buildCommandBuffers();
 		buildOffscreenCommandBuffer(); 
@@ -1075,6 +1099,12 @@ public:
 		if (!prepared)
 			return;
 		draw();
+		if (!paused)
+		{
+			meshRot.y += frameTimer * 10.0f;
+			updateUniformBuffers();
+			updateUniformBufferOffscreen();
+		}
 	}
 
 	virtual void viewChanged()