Resolve write-after-read hazard in extensions sample color_write_enable. (#1519)

Author: asuessenbach

samples/extensions/color_write_enable/color_write_enable.cpp

@@ -357,9 +357,9 @@ void ColorWriteEnable::setup_render_pass()
 	subpass_descriptions[1].pInputAttachments       = input_references.data();
 
 	// Subpass dependencies for layout transitions.
-	std::array<VkSubpassDependency, 3> dependencies = {};
+	std::array<VkSubpassDependency, 4> dependencies = {};
 
-	// External to color pass.
+	// External to color pass (for attachments whose first use is subpass 0).
 	dependencies[0].srcSubpass      = VK_SUBPASS_EXTERNAL;
 	dependencies[0].dstSubpass      = 0;
 	dependencies[0].srcStageMask    = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
@@ -368,24 +368,34 @@ void ColorWriteEnable::setup_render_pass()
 	dependencies[0].dstAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT | VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
 	dependencies[0].dependencyFlags = VK_DEPENDENCY_BY_REGION_BIT;
 
-	// Color pass to composition pass.
-	dependencies[1].srcSubpass      = 0;
+	// External to composition pass (for attachments whose first use is subpass 1).
+	// This is REQUIRED for the composition image (attachment 0) because its first use is subpass 1.
+	dependencies[1].srcSubpass      = VK_SUBPASS_EXTERNAL;
 	dependencies[1].dstSubpass      = 1;
-	dependencies[1].srcStageMask    = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
-	dependencies[1].dstStageMask    = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
-	dependencies[1].srcAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
-	dependencies[1].dstAccessMask   = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT;
+	dependencies[1].srcStageMask    = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
+	dependencies[1].dstStageMask    = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
+	dependencies[1].srcAccessMask   = VK_ACCESS_MEMORY_READ_BIT;
+	dependencies[1].dstAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT | VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
 	dependencies[1].dependencyFlags = VK_DEPENDENCY_BY_REGION_BIT;
 
-	// Composition pass to external.
-	dependencies[2].srcSubpass      = 1;
-	dependencies[2].dstSubpass      = VK_SUBPASS_EXTERNAL;
+	// Color pass to composition pass.
+	dependencies[2].srcSubpass      = 0;
+	dependencies[2].dstSubpass      = 1;
 	dependencies[2].srcStageMask    = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
-	dependencies[2].dstStageMask    = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
-	dependencies[2].srcAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT | VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
-	dependencies[2].dstAccessMask   = VK_ACCESS_MEMORY_READ_BIT;
+	dependencies[2].dstStageMask    = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
+	dependencies[2].srcAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
+	dependencies[2].dstAccessMask   = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT;
 	dependencies[2].dependencyFlags = VK_DEPENDENCY_BY_REGION_BIT;
 
+	// Composition pass to external.
+	dependencies[3].srcSubpass      = 1;
+	dependencies[3].dstSubpass      = VK_SUBPASS_EXTERNAL;
+	dependencies[3].srcStageMask    = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
+	dependencies[3].dstStageMask    = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
+	dependencies[3].srcAccessMask   = VK_ACCESS_COLOR_ATTACHMENT_READ_BIT | VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
+	dependencies[3].dstAccessMask   = VK_ACCESS_MEMORY_READ_BIT;
+	dependencies[3].dependencyFlags = VK_DEPENDENCY_BY_REGION_BIT;
+
 	// Create render pass.
 	VkRenderPassCreateInfo render_pass_create_info = {};
 	render_pass_create_info.sType                  = VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO;