From fb4187a916ba7b51694361fb6ebc113c1ebf0aad Mon Sep 17 00:00:00 2001
From: ShoufengYang <88227393+ShoufengYang@users.noreply.github.com>
Date: Tue, 3 Aug 2021 23:04:40 +0800
Subject: [PATCH] Update computeshader.cpp

There is a logical error that cause the first frame render error.  Since the graphic rendering need to sample the compute shader 's output image, so the compute command need to run  before the graphic rendering. If not, the graphic rendering will sample the gabage data (computer's output image) for the first frame and present on the display screen.This issue can be easy to be reproduced when the GPU device has a lower performance.
---
 examples/computeshader/computeshader.cpp | 41 ++++++++++++------------
 1 file changed, 20 insertions(+), 21 deletions(-)

diff --git a/examples/computeshader/computeshader.cpp b/examples/computeshader/computeshader.cpp
index dec255c4..bd475cc1 100644
--- a/examples/computeshader/computeshader.cpp
+++ b/examples/computeshader/computeshader.cpp
@@ -490,6 +490,13 @@ public:
 		// Semaphore for compute & graphics sync
 		VkSemaphoreCreateInfo semaphoreCreateInfo = vks::initializers::semaphoreCreateInfo();
 		VK_CHECK_RESULT(vkCreateSemaphore(device, &semaphoreCreateInfo, nullptr, &graphics.semaphore));
+	
+		// Signal the semaphore
+		VkSubmitInfo submitInfo = vks::initializers::submitInfo();
+		submitInfo.signalSemaphoreCount = 1;
+		submitInfo.pSignalSemaphores = &graphics.semaphore;
+		VK_CHECK_RESULT(vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE));
+		VK_CHECK_RESULT(vkQueueWaitIdle(queue));	
 	}
 
 	void prepareCompute()
@@ -559,13 +566,6 @@ public:
 		VkSemaphoreCreateInfo semaphoreCreateInfo = vks::initializers::semaphoreCreateInfo();
 		VK_CHECK_RESULT(vkCreateSemaphore(device, &semaphoreCreateInfo, nullptr, &compute.semaphore));
 
-		// Signal the semaphore
-		VkSubmitInfo submitInfo = vks::initializers::submitInfo();
-		submitInfo.signalSemaphoreCount = 1;
-		submitInfo.pSignalSemaphores = &compute.semaphore;
-		VK_CHECK_RESULT(vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE));
-		VK_CHECK_RESULT(vkQueueWaitIdle(queue));
-
 		// Build a single command buffer containing the compute dispatch commands
 		buildComputeCommandBuffer();
 	}
@@ -595,6 +595,19 @@ public:
 
 	void draw()
 	{
+		// Wait for rendering finished
+		VkPipelineStageFlags waitStageMask = VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT;
+
+		// Submit compute commands
+		VkSubmitInfo computeSubmitInfo = vks::initializers::submitInfo();
+		computeSubmitInfo.commandBufferCount = 1;
+		computeSubmitInfo.pCommandBuffers = &compute.commandBuffer;
+		computeSubmitInfo.waitSemaphoreCount = 1;
+		computeSubmitInfo.pWaitSemaphores = &graphics.semaphore;
+		computeSubmitInfo.pWaitDstStageMask = &waitStageMask;
+		computeSubmitInfo.signalSemaphoreCount = 1;
+		computeSubmitInfo.pSignalSemaphores = &compute.semaphore;
+		VK_CHECK_RESULT(vkQueueSubmit(compute.queue, 1, &computeSubmitInfo, VK_NULL_HANDLE));	
 		VulkanExampleBase::prepareFrame();
 
 		VkPipelineStageFlags graphicsWaitStageMasks[] = { VK_PIPELINE_STAGE_VERTEX_INPUT_BIT, VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT };
@@ -612,20 +625,6 @@ public:
 		VK_CHECK_RESULT(vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE));
 
 		VulkanExampleBase::submitFrame();
-
-		// Wait for rendering finished
-		VkPipelineStageFlags waitStageMask = VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT;
-
-		// Submit compute commands
-		VkSubmitInfo computeSubmitInfo = vks::initializers::submitInfo();
-		computeSubmitInfo.commandBufferCount = 1;
-		computeSubmitInfo.pCommandBuffers = &compute.commandBuffer;
-		computeSubmitInfo.waitSemaphoreCount = 1;
-		computeSubmitInfo.pWaitSemaphores = &graphics.semaphore;
-		computeSubmitInfo.pWaitDstStageMask = &waitStageMask;
-		computeSubmitInfo.signalSemaphoreCount = 1;
-		computeSubmitInfo.pSignalSemaphores = &compute.semaphore;
-		VK_CHECK_RESULT(vkQueueSubmit(compute.queue, 1, &computeSubmitInfo, VK_NULL_HANDLE));
 	}
 
 	void prepare()