Could validate stageFlags for INPUT_ATTACHMENT?

[karl-lunarg]

Issue by toten (MIGRATED)
Friday Nov 03, 2017 at 07:03 GMT
Originally opened as KhronosGroup/Vulkan-LoaderAndValidationLayers#2178

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My case is:

When creating VkDescriptorSetLayoutBinding structure, the descriptorType is VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT; from the spec, the stageFlags must be VK_SHADER_STAGE_FRAGMENT_BIT. However I forgot setting the stageFlags (partially due to the code is originally copied from others), so the input_attachment reading in fragment shader returns black. It took me one or two hours to finally figure out where the problem is.

Just curious if the core-validation layer or parameter-validation layer could check this, and help to locate the problem quickly.

Thanks a lot.

[karl-lunarg]

Comment by tobine (MIGRATED)
Friday Nov 03, 2017 at 17:31 GMT

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This is missing check VALIDATION_ERROR_04e00bcc.

@toten note from spec that stageFlags can be 0 or *FRAGMENT_BIT:

If descriptorType is VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT and descriptorCount is not 0, then stageFlags must be 0 or VK_SHADER_STAGE_FRAGMENT_BIT

Not sure what your stageFlags was, but if it was 0, the new validation check won't catch that case.

[karl-lunarg]

Comment by chrisforbes (MIGRATED)
Thursday Nov 09, 2017 at 22:03 GMT

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@tobine can we justify emitting a warning for stageFlags=0? We already have the option of descriptorCount=0 for making unusable placeholder bindings.

[karl-lunarg]

Comment by tobine (MIGRATED)
Friday Nov 10, 2017 at 16:37 GMT

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Well, if @toten had stageFlags=0, then I'd say the fact that the warning would have been a help in that case justifies it. At least until/unless someone else complains about the warning with a reasonable use case that requires stageFlags=0. I can't think of a good case offhand as the descriptorCount=0 option is already there as you said for unusable bindings.
@toten please confirm if your stageFlags was 0 and we can put in a warning for that case to assist other users in the future.

[karl-lunarg]

Comment by toten (MIGRATED)
Monday Nov 13, 2017 at 02:20 GMT

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I used the api-dump layer (also debug) and could confirm the stageFlags was 0. The input-attachment loading returns black color when stageFlags was 0.

When I explicitly set to VK_SHADER_STAGE_FRAGMENT_BIT, input-attachment loading works as expected. BTW, the api-dump layer returns:
stageFlags: VkShaderStageFlags = 16 (VK_SHADER_STAGE_FRAGMENT_BIT | VK_SHADER_STAGE_ALL_GRAPHICS | VK_SHADER_STAGE_ALL)
It looks a little strange that | VK_SHADER_STAGE_ALL_GRAPHICS | VK_SHADER_STAGE_ALL ??

Thanks all the help!

[jzulauf-lunarg]

Triage notes: This can't be done at bindtime, but could be added to the validation of the subpass attachments at CmdBeginRenderPass time.

[mark-lunarg]

Moving this warning issue to best practices tracking issue, #24.