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Fix swapped semaphore/stage-mask pairing in the compute chapter #483

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Fix swapped semaphore/stage-mask pairing in the compute chapter #483

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8 changes: 7 additions & 1 deletion en/11_Compute_Shader.adoc
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Expand Up @@ -583,6 +583,12 @@ The first submit to the compute queue updates the particle positions using the c

=== Synchronizing graphics and compute

NOTE: The binary-semaphore-and-fence approach below is presented first because it builds directly on
the synchronization primitives introduced in earlier chapters. The attached example program, however,
uses only the timeline-semaphore approach from the "Timeline semaphores" section below - it never creates
the `computeInFlightFences`/`computeFinishedSemaphores` shown here. Read this section for the concepts,
then see the next section for what's actually implemented.

Synchronization is an important part of Vulkan, even more so when doing compute in conjunction with graphics.
Wrong or lacking synchronization may result in the vertex stage starting to draw (=read) particles while the compute shader hasn't finished updating (=write) them (read-after-write hazard), or the compute shader could start updating particles that are still in use by the vertex part of the pipeline (write-after-read hazard).

Expand Down Expand Up @@ -644,7 +650,7 @@ We then use these to synchronize the compute buffer submission with the graphics
recordCommandBuffer(imageIndex);

vk::Semaphore waitSemaphores[] = {**presentCompleteSemaphore[frameIndex], **computeFinishedSemaphores[frameIndex]};
vk::PipelineStageFlags waitDestinationStageMask[] = { vk::PipelineStageFlagBits::eVertexInput, vk::PipelineStageFlagBits::eColorAttachmentOutput };
vk::PipelineStageFlags waitDestinationStageMask[] = { vk::PipelineStageFlagBits::eColorAttachmentOutput, vk::PipelineStageFlagBits::eVertexInput };
const vk::SubmitInfo submitInfo( waitSemaphores, waitDestinationStageMask, {**commandBuffers[frameIndex]}, {**renderFinishedSemaphore[frameIndex]} );
graphicsQueue->submit(submitInfo, **inFlightFences[frameIndex]);
----
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