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Document the single-time command buffer change in Generating Mipmaps #490

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Document the single-time command buffer change in Generating Mipmaps #490

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20 changes: 17 additions & 3 deletions en/09_Generating_Mipmaps.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -130,8 +130,19 @@ depthImageView = createImageView(depthImage, depthFormat, vk::ImageAspectFlagBit
textureImageView = createImageView(*textureImage, vk::Format::eR8G8B8A8Srgb, vk::ImageAspectFlagBits::eColor, mipLevels);
----

In the previous chapter, `createTextureImage` called `beginSingleTimeCommands` and
`endSingleTimeCommands` three separate times: once around the layout transition, once around the
buffer-to-image copy, and once around the final transition to shader-read layout. Generating
mipmaps adds a blit and two more layout transitions for every mip level, and opening a new command
buffer for each of those would be wasteful. So instead, `createTextureImage` will call
`beginSingleTimeCommands` once at the start, record the transition, the copy, and all of
`generateMipmaps` into that same command buffer, and only call `endSingleTimeCommands` once, at
the very end. `beginSingleTimeCommands` and `endSingleTimeCommands` themselves haven't changed -
we're just calling them less often:

[,c++]
----
vk::raii::CommandBuffer commandBuffer = beginSingleTimeCommands();
transitionImageLayout(commandBuffer, textureImage, vk::ImageLayout::eUndefined, vk::ImageLayout::eTransferDstOptimal, mipLevels);
----

Expand Down Expand Up @@ -315,14 +326,17 @@ Finally, we insert one more pipeline barrier.
This barrier transitions the last mip level from `vk::ImageLayout::eTransferDstOptimal` to `vk::ImageLayout::eShaderReadOnlyOptimal`.
The loop didn't handle this, since the last mip level is never blitted from.

Finally, add the call to `generateMipmaps` in `createTextureImage`:
Finally, add the call to `generateMipmaps` in `createTextureImage`, and end the single-time
command buffer we opened at the start of this chapter now that every operation has been recorded
into it:

[,c++]
----
transitionImageLayout(*textureImage, vk::ImageLayout::eUndefined, vk::ImageLayout::eTransferDstOptimal, mipLevels);
copyBufferToImage(stagingBuffer, *textureImage, static_cast<uint32_t>(texWidth), static_cast<uint32_t>(texHeight));
transitionImageLayout(commandBuffer, textureImage, vk::ImageLayout::eUndefined, vk::ImageLayout::eTransferDstOptimal, mipLevels);
copyBufferToImage(commandBuffer, stagingBuffer, textureImage, static_cast<uint32_t>(texWidth), static_cast<uint32_t>(texHeight));
//transitioned to vk::ImageLayout::eShaderReadOnlyOptimal while generating mipmaps
generateMipmaps(commandBuffer, textureImage, texWidth, texHeight, mipLevels);
endSingleTimeCommands(std::move(commandBuffer));
----

Our texture image's mipmaps are now filled.
Expand Down
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