[Mesa-dev] [PATCH] nir: Lower interp_var_at_* like a normal load_var for flat inputs.

[Kenneth Graunke]

"flat centroid" and "flat sample" both just mean "flat", so we should
ignore interpolateAtCentroid/Sample and just return the flat value.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97032
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/compiler/nir/nir_lower_io.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/compiler/nir/nir_lower_io.c b/src/compiler/nir/nir_lower_io.c
index bf8296f..b36836f 100644
--- a/src/compiler/nir/nir_lower_io.c
+++ b/src/compiler/nir/nir_lower_io.c
@@ -340,6 +340,10 @@ lower_interpolate_at(nir_intrinsic_instr *intrin, struct lower_io_state *state,
 
    assert(var->data.mode == nir_var_shader_in);
 
+   /* Ignore interpolateAt() for flat variables - flat is flat. */
+   if (var->data.interpolation == INTERP_MODE_FLAT)
+      return lower_load(intrin, state, NULL, offset);
+
    nir_intrinsic_op bary_op;
    switch (intrin->intrinsic) {
    case nir_intrinsic_interp_var_at_centroid:
-- 
2.9.0