Validation Errors

[dschuechter]

Hey, I am currently following your great tutorial series. Thanks for your great work!

I ran into validation errors in Vulkan Tutorial #018 and Vulkan Tutorial #024. Since I am quiet new to Vulkan and C++ I am a bit lost.

In Episode 18:

Validation errors:
[.../Vulkan/src/vulkan_base/vulkan_device.cpp:5]: Validation Error: [ SYNC-HAZARD-WRITE-AFTER-READ ] Object 0: handle = 0x557fb8f85db0, type = VK_OBJECT_TYPE_QUEUE; | MessageID = 0x376bc9df | vkQueueSubmit(): Hazard WRITE_AFTER_READ for entry 0, VkCommandBuffer 0x557fbb2bba00[], Submitted access info (submitted_usage: SYNC_IMAGE_LAYOUT_TRANSITION, command: vkCmdBeginRenderPass, seq_no: 1, renderpass: VkRenderPass 0xd5b26f0000000010[], reset_no: 88). Access info (prior_usage: SYNC_PRESENT_ENGINE_SYNCVAL_PRESENT_ACQUIRE_READ_SYNCVAL, read_barriers: VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT|VK_PIPELINE_STAGE_2_BOTTOM_OF_PIPE_BIT, , batch_tag: 693, vkAcquireNextImageKHR aquire_tag:693: VkSwapchainKHR 0xee647e0000000009[], image_index: 2image: VkImage 0xe88693000000000c[])

I identified the problem to be this line:

    VkPipelineStageFlags waitMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; 

If you change it to

    VkPipelineStageFlags waitMask = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT;

the validation errors disappear.

In Episode 24

[.../Vulkan/src/vulkan_base/vulkan_device.cpp:5]: Validation Error: [ SYNC-HAZARD-WRITE-AFTER-
READ ] Object 0: handle = 0x55ff83f9aa80, type = VK_OBJECT_TYPE_QUEUE; | MessageID =
0x376bc9df | vkQueueSubmit():  Hazard WRITE_AFTER_READ for entry 0, VkCommandBuffer
0x55ff863110a0[], Submitted access info (submitted_usage: SYNC_IMAGE_LAYOUT_TRANSITION, 
command: vkCmdBeginRenderPass, seq_no: 1, renderpass: VkRenderPass 0xd5b26f0000000010[],
reset_no: 162). Access info (prior_usage: 
SYNC_PRESENT_ENGINE_SYNCVAL_PRESENT_ACQUIRE_READ_SYNCVAL, read_barriers: 
K_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT|
VK_PIPELINE_STAGE_2_BOTTOM_OF_PIPE_BIT, , batch_tag: 1301, vkAcquireNextImageKHR 
quire_tag:1301: VkSwapchainKHR 0xee647e0000000009[], image_index: 2image: VkImage 
0xe88693000000000c[]).

The same validation errors are reproducable with your code.

I am running an up-to-date Arch Linux with Vulkan (Instance Version 1.3.279).

[Pilzschaf]

Thank you for pointing this out.
It looks like I forgot to add a barrier to be 100% correct when it comes to synchronization.
There are 2 options to add this barrier: Either you could add the barrier as a vkCmdPipelineBarrier before beginning the renderpass or you could add it as a subpass dependency in the renderpass creation. The latter would look like this:

VkSubpassDependency dependencies[] = {
{.srcSubpass = VK_SUBPASS_EXTERNAL, .dstSubpass = 0, 
.srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, .dstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, 
.srcAccessMask = 0, .dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT, .dependencyFlags = 0},
};

// Then add this dependency as part of the VkRenderPassCreateInfo
createInfo.pDependencies = dependencies;
createInfo.dependencyCount = ARRAY_COUNT(dependencies);

The subpass external dependency makes sure that the image is actually available to be written into with 'VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT' by waiting at our 'VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT'