Advanced blend operations are lowered in the fragment shader using
nir_lower_blend, with the actual blending done via framebuffer fetch.
For monolithic pipelines, lowering happens at pipeline compilation.
For GPL, lowering happens at link time when blend state is known.
For shader objects, lowering happens at draw time with the result
cached until blend parameters, fragment shader, or color write state
changes.
The lvp_nir_lower_blend() helper handles the IO lowering sandwich
required by nir_lower_blend: lower derefs to IO intrinsics, run the
blend lowering, then convert back to derefs for llvmpipe.
Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39612>