tree 0ca517497db4b4e8444b0110c02a7a51d1e23ed7
parent 5c3720824f2b33ee10790c6259949906672d01ad
author Nicolas Capens <capn@google.com> 1583986800 -0400
committer Nicolas Capens <nicolascapens@google.com> 1584026365 +0000

Document single-level YCbCr image assumption

We currently rely on limiting the mipmap level count of YCbCr images
and the presence of sampler YCbCr conversion to disable mipmapping.

This is valid, but fragile. The Vulkan 1.2 spec guarantees that when
sampler Y'CbCr conversion is used, the image view must have a Y'CbCr
format:

"If the descriptor refers to a sampler that performs Y'CbCr conversion,
 the sampler must only be used to sample the image in the same
 descriptor."

"If the image view is to be used with a sampler which supports sampler
 Y'CbCr conversion, an identically defined object of type
 VkSamplerYcbcrConversion to that used to create the sampler must be
 passed to vkCreateImageView in a VkSamplerYcbcrConversionInfo included
 in the pNext chain of VkImageViewCreateInfo. Conversely, if a
 VkSamplerYcbcrConversion object is passed to vkCreateImageView, an
 identically defined VkSamplerYcbcrConversion object must be used when
 sampling the image."

"maxMipLevels is the maximum number of mipmap levels. maxMipLevels must
 be equal to the number of levels in the complete mipmap chain based on
 the maxExtent.width, maxExtent.height, and maxExtent.depth, except when
 one of the following conditions is true, in which case it may instead
 be 1:
  * ...
  * image format is one of those listed in Formats requiring sampler
    Y′CBCR conversion for VK_IMAGE_ASPECT_COLOR_BIT image views"

Bug: b/151263485
Change-Id: Ibb8e3fe34ecda04d6fb41308437fa4c66815f1fb
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42228
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>