Confirm prohibited formats

[lexaknyazev]

From the Section 3.2:

It can be any value defined in core Vulkan 1.2, future core versions or registered Vulkan extensions, except for values listed in Table 1, “Prohibited Formats” and any *SCALED*, *422*, *[2-9]PLANE* or *[34]PACK16* formats added in future.

• The table includes 6 single-plane packed 10- and 12-bit formats like R10X6_UNORM_PACK16 and R12X4G12X4B12X4A12X4_UNORM_4PACK16 with no explanation in the rationale section afterwards. Arguably, they could be allowed.
• The wildcard template strings could be slightly optimized: all formats that have 3PACK16 also have 2PLANE or 3PLANE.

[MarkCallow]

I have have misunderstood what some of those formats really are and thought they were multi-plane.. The intent is to prohibit packed formats that have an equivalent rg, rgb or rgba format, e.g. the *_PACK32 formats, and multi-plane formats.

Happy to accept a PR to modify the list of prohibited formats. An equivalent change must be made to the lib/mkvkformatfiles script in the KTX-Software repo which generates the file vkformat_check.c. Please create a PR for that too.

[lexaknyazev]

OK. In that case, we should also allow single-plane subsampled formats. For reference, here's a full list of currently prohibited single-plane formats.

• 10-bit channels padded to 16 bits:

  R10X6_UNORM_PACK16
  R10X6G10X6_UNORM_2PACK16
  R10X6G10X6B10X6A10X6_UNORM_4PACK16

• 12-bit channels padded to 16 bits:

  R12X4_UNORM_PACK16
  R12X4G12X4_UNORM_2PACK16
  R12X4G12X4B12X4A12X4_UNORM_4PACK16

• 2x1 blocks (green values are unique, red and blue are duplicated)

  • 8-bit channels

    G8B8G8R8_422_UNORM
    B8G8R8G8_422_UNORM

  • 10-bit channels padded to 16 bits

    G10X6B10X6G10X6R10X6_422_UNORM_4PACK16
    B10X6G10X6R10X6G10X6_422_UNORM_4PACK16

  • 12-bit channels padded to 16 bits

    G12X4B12X4G12X4R12X4_422_UNORM_4PACK16
    B12X4G12X4R12X4G12X4_422_UNORM_4PACK16

  • 16-bit channels

    G16B16G16R16_422_UNORM
    B16G16R16G16_422_UNORM

[MarkCallow]

Thanks @lexaknyazev. @fluppeteer DFD-wise are there any problems with allowing these?