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NikoandClaude Opus 5.5 16ea32c97d feat(agc): blend into color targets with a reversed component order
8_8_8_8 and 16_16_16_16 targets with COMP_SWAP 2 or 3 keep the exported
alpha in their first channel and red or blue in their fourth, so a plain
Vulkan blend would run the alpha equation on a color channel. Such draws
threw "blending into a color target with a reversed component order is
not implemented" (Gran Turismo 7, #4782).

The AMD SI and CIK register references describe CB_TARGET_MASK in the
order of components after blending and before COMP_SWAP is applied, and
RADV programs CB_BLENDn_CONTROL without regard to the swap while it
renders R4G4B4A4, B4G4R4A4, R5G5B5A1 and B5G5R5A1 through SWAP_STD_REV
and SWAP_ALT_REV and passes the CTS blend tests on Navi10. The color
block is therefore taken to blend in export order: the alpha equation
and source-alpha factors use the exported alpha and the destination
alpha is the first channel.

TranslateReversedBlend keeps the factor pairs Vulkan applies per channel
in the pipeline. Other source factors are computed by the pixel shader
from its MRT0 export (clamped for UNORM targets, as BLEND_CLAMP says)
and handed to the blend as a dual-source second color, which the
fragment output post-pass adds at location 0 index 1; when both
positions need it, the export is premultiplied by its source factor.
The code is a pipeline specialization, serialized in request version
26, and stays out of the prepared shader key.

sRGB, SNORM and integer targets, constant and second-source factors,
destination alpha in the color equation, destination factors the two
equations do not share, different color and alpha operations, MIN or
MAX with factors other than ONE, other color exports when the shader
computes factors, and devices without dualSrcBlend still throw, now
with the blend control, mapping and format in the message.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-15 12:51:27 +02:00
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