sRGB texture formats are defined as having an sRGB-encoded alpha channel in vk.xml

[theagentd]

In the formats section of vk.xml, sRGB formats are listed as having sRGB encoded alpha channels.

However, for VK_FORMAT_R8G8B8A8_SRGB the spec states the following:

VK_FORMAT_R8G8B8A8_SRGB specifies a four-component, 32-bit unsigned normalized format that has an 8-bit R component stored with sRGB nonlinear encoding in byte 0, an 8-bit G component stored with sRGB nonlinear encoding in byte 1, an 8-bit B component stored with sRGB nonlinear encoding in byte 2, and an 8-bit A component in byte 3.

As such, sRGB formats with alpha channels should have their alpha channels listed as having a numericFormat of "UNORM", not "SRGB".

Example:

        <format name="VK_FORMAT_R8G8B8A8_SRGB" class="32-bit" blockSize="4" texelsPerBlock="1">
            <component name="R" bits="8" numericFormat="SRGB"/>
            <component name="G" bits="8" numericFormat="SRGB"/>
            <component name="B" bits="8" numericFormat="SRGB"/>
            <component name="A" bits="8" numericFormat="SRGB"/> <!--Incorrect, should be UNORM-->
        </format>

I've found that all the sRGB formats with alpha channels have this issue:

• VK_FORMAT_R8G8B8A8_SRGB
• VK_FORMAT_B8G8R8A8_SRGB
• VK_FORMAT_A8B8G8R8_SRGB_PACK32
• VK_FORMAT_BC1_RGBA_SRGB_BLOCK
• VK_FORMAT_BC2_SRGB_BLOCK
• VK_FORMAT_BC3_SRGB_BLOCK
• VK_FORMAT_BC7_SRGB_BLOCK
• VK_FORMAT_ETC2_R8G8B8A1_SRGB_BLOCK
• VK_FORMAT_ETC2_R8G8B8A8_SRGB_BLOCK
• All ASTC formats with sRGB encoding:
  • VK_FORMAT_ASTC_4x4_SRGB_BLOCK
  • VK_FORMAT_ASTC_5x4_SRGB_BLOCK
  • VK_FORMAT_ASTC_5x5_SRGB_BLOCK
  • VK_FORMAT_ASTC_6x5_SRGB_BLOCK
  • VK_FORMAT_ASTC_6x6_SRGB_BLOCK
  • VK_FORMAT_ASTC_8x5_SRGB_BLOCK
  • VK_FORMAT_ASTC_8x6_SRGB_BLOCK
  • VK_FORMAT_ASTC_8x8_SRGB_BLOCK
  • VK_FORMAT_ASTC_10x5_SRGB_BLOCK
  • VK_FORMAT_ASTC_10x6_SRGB_BLOCK
  • VK_FORMAT_ASTC_10x8_SRGB_BLOCK
  • VK_FORMAT_ASTC_10x10_SRGB_BLOCK
  • VK_FORMAT_ASTC_12x10_SRGB_BLOCK
  • VK_FORMAT_ASTC_12x12_SRGB_BLOCK
• VK_FORMAT_PVRTC1_2BPP_SRGB_BLOCK_IMG
• VK_FORMAT_PVRTC1_4BPP_SRGB_BLOCK_IMG
• VK_FORMAT_PVRTC2_2BPP_SRGB_BLOCK_IMG
• VK_FORMAT_PVRTC2_4BPP_SRGB_BLOCK_IMG

[spencer-lunarg]

@theagentd thanks for pointing this out, this is indeed wrong and I will get a fix in