[Impeller] generate mip level N from N-1 in Vulkan backend. #51749
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When I first wrote this, my mental model was that generating data for mip level N from N-1 was similar to making a JPEG from a JPEG. Instead of making a JPEG of increasingly smaller size from a base original. In the OpenGL spec, this is all implementation dependent. So I can't tell which one is correct. But if this matches what the other backends are doing, we should go for it. |
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In writing a test for this I found #51761 |
| barrier.srcAccessMask = vk::AccessFlagBits::eTransferWrite; | ||
| barrier.dstAccessMask = vk::AccessFlagBits::eTransferRead; | ||
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| cmd.pipelineBarrier(vk::PipelineStageFlagBits::eTransfer, |
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Just to make this easier to read, add a comment about why the barrier is necessary. I'll attempt to jot down how I read it but please proofread.
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Comment Suggestion:
We just finished writing to the previous (N-1) mip level. These were initialized to
TransferDstearler. We are now going to read from it to write to the current level (N) . So it must be converted toTransferSrc.
| barrier.srcAccessMask = vk::AccessFlagBits::eTransferRead; | ||
| barrier.dstAccessMask = vk::AccessFlagBits::eShaderRead; | ||
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| cmd.pipelineBarrier(vk::PipelineStageFlagBits::eTransfer, |
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Comment Suggestion:
Now that the blit is done, the image at the previous level (N-1) is done reading from (
TransferSrc). Now we must prepare it to be read from a shader (ShaderReadOnly).
| // Transition the base mip level to transfer-src layout so we can read from | ||
| // it and transition the rest to dst-optimal since they are going to be | ||
| // written to. | ||
| InsertImageMemoryBarrier( |
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Comment Suggestion:
Initialize all mip levels to be in
TransferDstmode. Later, in a loop, after writing to that mip level, we'll first switch its layout toTransferSrcto prepare the mip level after it, use the image as the source of the blit, before finally switching it toShaderReadOnlyso its available for sampling in a shader.
| barrier.srcAccessMask = vk::AccessFlagBits::eTransferWrite; | ||
| barrier.dstAccessMask = vk::AccessFlagBits::eShaderRead; | ||
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| cmd.pipelineBarrier(vk::PipelineStageFlagBits::eTransfer, |
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Comment SUggestion:
The very last mip level is still in
TransferDstand must be converted toShaderReadOnly.
| mip_count - 1 // mip level count | ||
| ); | ||
| 0u, // mip level | ||
| mip_count); |
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Nit: Missing last comment.
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jonahwilliams
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…145994) flutter/engine@b16c0f1...7176173 2024-03-29 [email protected] [Impeller] generate mip level N from N-1 in Vulkan backend. (flutter/engine#51749) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll Please CC [email protected],[email protected],[email protected] on the revert to ensure that a human is aware of the problem. To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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Uses the mipmap implementation from https://vulkan-tutorial.com/Generating_Mipmaps .
Today we generate all mip levels from mip level 0, which results in lost data. Instead we need to use the previous mip level