possible race in staging upload for lightmaps about vkquake HOT 6 CLOSED

I'm not sure if I understand. The lightmap only needs to be uploaded before the command buffer is executing on the GPU in the next frame. Is that not the case?

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Oh so the lightmap update lags by a frame, oh if so then it it's fine, I though it was update the lightmap for the current frame and thus failing to actually upload it.

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Define "current frame"?

GPU rendering is inherently asynchronous. While the CPU is recording command buffers for the next frame, the GPU is executing the ones recorded a frame earlier.

This also includes the DMA transfers executed by the GPU to upload the lightmap. Essentially vkCmd* calls do nothing until vkQueueSubmit (and even then are only queued and might not execute immediately).

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So in this case you are preparing two command buffers, one staging to upload the lightmap, and one main command buffer. The staging command buffer doesn't get submitted before the main command buffer does. So current frame I mean what the CPU is going to submit next.

So current order is

• frame 1
  Submit Staging
  Update Staging with lightmap
  Submit Main Command
• frame 2
  Submit Staging

The staging lightmap update won't have any effect on the current main command buffer being uploaded.

If that is how quake works, that is fine, it just seemed confusing to be updating the lightmap mid-frame when the results aren't used until next frame.

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I will double check the logic if I find time. If there is an issue it would just delay the update by a frame.

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You are right, the buffer submit has to be done in end frame, not begin frame. No idea what I was thinking there. Fixed by a6dbe10

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