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| asyncgpureadback [2021/12/25 01:00] – created archo | asyncgpureadback [2025/01/15 04:35] (current) – external edit 127.0.0.1 |
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| In at least 2018.2 and possibly other versions there appears to be an undocumented bug that readback requests mess with the command buffer: | In at least 2018.2 and possibly other versions there appears to be an undocumented bug that readback requests mess with the command buffer: |
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| * readback requests inserted in the middle will split the command buffer (which is fine) however the second part will have LoadAction=Clear which effectively destroys everything rendered before the request | * Readback requests inserted in the middle will split the command buffer((this is reasonable)), however the second part will have LoadAction=Clear which destroys everything rendered before the request |
| * readback requests inserted at the end will make Unity skip ''presentDrawable'' which results in the screen not being updated, and the behavior may differ between devices: | * Readback requests inserted at the end will make Unity skip ''presentDrawable'' which results in the screen not being updated, and the behavior differs between devices: |
| * those configured for debugging or at least currently debugging - can't see anything happening in the game but input is accepted and things continue to work | * Those configured for debugging or currently debugging: nothing renders but input is accepted and the game continues to run. |
| * others - crash caused by an OS timeout | * Others: crash caused by an OS timeout |
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| The workaround is to move the readback request to the beginning of the next frame. | The workaround is to move the readback request to the beginning of the next frame. |
| ==== Random failures ==== | ==== Random failures ==== |
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| In some cases<sup>[//[[:wiki:tag:research-needed|research needed]]//]</sup> (observed at least on 2018.2.21 when exiting play mode and sometimes while paused in editor), the callback will be called but when attempting to call [[https://docs.unity3d.com/ScriptReference/Rendering.AsyncGPUReadbackRequest.GetData.html|GetData]], it will throw an exception. | In some cases<sup>[//[[:wiki:tag:research-needed|research needed]]//]</sup>, the callback will be called but when attempting to call [[https://docs.unity3d.com/ScriptReference/Rendering.AsyncGPUReadbackRequest.GetData.html|GetData]], it will throw an exception.((observed at least on 2018.2.21 when exiting play mode and sometimes while paused in editor)) |
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| The cause is unknown, it does not appear to be detectable beforehand (all [[https://docs.unity3d.com/ScriptReference/Rendering.AsyncGPUReadbackRequest.html|AsyncGPUReadbackRequest]] properties indicate that it's a valid completed request) but it seems to be safe to catch and ignore this exception. | The cause is unknown, it does not appear to be detectable beforehand. All [[https://docs.unity3d.com/ScriptReference/Rendering.AsyncGPUReadbackRequest.html|AsyncGPUReadbackRequest]] properties indicate that it's a valid completed request. It seems to be safe to catch and ignore this exception. |
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