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 <[email protected]>
Requests replayed from versions 22 to 24 now re-serialize at version 29 with
the default quad pixel mask (0xf) and quad sample masks (0xffff) after the dither and front-face flags, plus the empty linked call fallback list.
The front-face VGPR was always +1.0 / -1.0, which is its form only while
FRONT_FACE_ALL_BITS is clear (current Mesa reads it with fgt 0 / fsign).
With the bit set, as Mesa 22.0 RADV programs it, a back face reads 0 and
a front face non-zero: ACO then tests it with v_cmp_lg_u32 0. Uncharted:
Legacy of Thieves Collection (PPSA05684) sets the bit and its two-sided
cloth shaders test v_cmp_lt_u32 0, so -1.0 (0xbf800000) made every back
face a front face: the insides of the menu skeleton's rags kept their
front normals and were lit white by the spot light behind them.
The pixel stage info now carries the bit (request version 26, cache and
draw keys), the decode reads SPI_BARYC_CNTL when FRONT_FACE is an active
input, and the translator turns the builtin into 0xffffffff / 0. The
exact front value is not measured (docs/dev/debt/shader.md).
AI-assisted: yes
An s_swappc_b64 whose target is not resolved compiles to a faulting call
only at the fallback the table-call linker emits; the linker lists those
calls in the request (GuestContext::linkedCallFallbacks), and every other
computed call is refused at compile time again, as on main. The new
agc_driver_compute_table_calls test runs a linked two-record table on
Vulkan in wave32 and wave64, with SCC 0 and 1 reaching the callee, and a
record past the table reporting the UnlinkedCall fault.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
