Do the _WRITE_BIT destination access masks imply _READ_BIT access scope?

user_2413857 0
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I think the question is clear, but in case the answer is no I'll describe the conundrum I have:

Minimal setup so a single render pass with a single subpass. Two attachments: color and depth, rendering a cube. The Depth attachment layouts (initial, mid, final) are:

  • VK_IMAGE_LAYOUT_UNDEFINED
  • VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL
  • VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL

So there's one automatic layout transition. I know that because of my .loadOp = VK_ATTACHMENT_LOAD_OP_CLEAR, I'll get a write-after-write warning If I don't make it visible. So I'll use this subpass dependency:

constexpr VkSubpassDependency in_dependency{
    .srcSubpass = VK_SUBPASS_EXTERNAL,
    .dstSubpass = 0,
    .srcStageMask = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT,
    .dstStageMask = VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT,
    .srcAccessMask = 0,
    .dstAccessMask = VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT
};

This targets the early fragment test because that's where the depth att gets clear-loaded. But: Don't I also need to include the _READ_BIT in my .dstAccessMask? Sync validation doesn't seem to care, but I think I do unless I missed some rule about the write visibility implying a read visibility?

In case there is such a thing, a pointer to the spec would be nice.

vulkan
1 Answers

WRITE does not include READ. This is simply a matter of the operation in question.

Clearing an image uses the WRITE access mode. It does not use the READ access mode. So there's is no further hazard as far as clearing is concerned.

Once the image is cleared, the subpass can begin executing. Since subpass execution happens-after the clearing operation, there's no need for any further dependency.

user_7340690
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