D848 - A ten-bit unorm target is drawn and written back as it is held

Status: decided Date: 2026-10-14

A colour target whose CB_COLOR0_INFO names COLOR_2_10_10_10, NUMBER_UNORM and SWAP_STD holds red, green and blue in ten bits each from the low end, and alpha in the top two, four bytes a texel. It lies by the 32-bpp layout. It is drawn through a Vulkan A2B10G10R10_UNORM_PACK32 attachment of the same format, whose bits are laid out the same way, so seeding and write-back move the guest's words untouched (D773, D844, D847). Any other swap or number type stays refused.

Why: Mesa targets a format of 10-10-10-2 bits, red first, at COLOR_2_10_10_10 (ac_formats.c 536), and SWAP_STD on four channels is XYZW (612). Grand Theft Auto V's fifth draw writes a 32 x 32 target of it, once its first four run. Blending on A2B10G10R10_UNORM_PACK32 is required of every Vulkan implementation.

Rejected:

• Drawing it through an eight-bit attachment: two bits of each colour channel would be lost on write-back.