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The Render Pass dependency from the well-known Vulkan tutorial from Sascha Willems looks like this:

.srcSubpass = VK_SUBPASS_EXTERNAL;
.dstSubpass = 0;
.srcStageMask =
  VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT | 
  VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
.srcAccessMask = 0;
.dstStageMask =
  VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT |
  VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
.dstAccessMask =
  VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT |
  VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;

The question is, why do we specify EARLY_FRAGMENT stage in srcStageMask? We are waiting for the COLOR_ATTACHMENT stage to complete, which means that all earlier render stages (including EARLY_FRAGMENT) will also be completed - isn't that enough?

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  • Precisely which sample and which render pass? What stage masks are needed will depend on what the render pass is doing in that specific instance. Commented Jun 8 at 20:50
  • 1
    In general I'd say that srcStageMask=EARLY_FRAGMENT_TESTS does seem odd for a source though. Depth/stencil is specified to be written at LATE_FRAGMENT_TESTS, so you can't safely "source" from EARLY unless it's read-only, at which point you're not really sourcing anything because it must already be in memory. Commented Jun 8 at 20:55
  • I got this from vulkan-tutorial.com. This is the main (and only) render pass (color+depth). But let me rephrase the question: doesn't the above code, regardless of context, mean the following: all stages from the srcStageMask must be completed before the stages from the dstAccessMask? If so, then EARLY_FRAGMENT stage from the srcStageMask will be completed before the COLOR_ATTACHMENT anyway, and we don't need to specify it? And yes, I mean only the completion of stages, without memory availability. Commented Jun 10 at 7:57
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    That would be my understanding too, yes ... Commented Jun 10 at 19:09
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