[Mesa-dev] [PATCH v2] st/mesa: don't force per-sample interp if only sampleid/pos are used

[Ilia Mirkin]

The OES extensions clarify this behaviour to differentiate between
per-sample invocation and per-sample interpolation. Using sampleid/pos
will force per-sample invocation but not per-sample interpolation.

See https://www.khronos.org/bugzilla/show_bug.cgi?id=1462

Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak at amd.com> (v1)

v1 -> v2:
  set key.persample_shading in the same way as raster->force_persample_interp
  except with an inverted dep on st->force_persample_in_shader
---

I realized that my old method would end up setting key.persample_shading when
the shader used sample id/sample pos. Rather than futz around with the
condition or add more helpers, this just reuses the current logic for setting
raster->force_persample_interp but flips the dependency on whether it has to be
done by hand or not. (And uses the semi-new mesa_geometric_samples helper.)

 src/mesa/state_tracker/st_atom_shader.c | 13 +++++--------
 src/mesa/state_tracker/st_program.c     |  4 ----
 2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/src/mesa/state_tracker/st_atom_shader.c b/src/mesa/state_tracker/st_atom_shader.c
index a88f035..f7e85c1 100644
--- a/src/mesa/state_tracker/st_atom_shader.c
+++ b/src/mesa/state_tracker/st_atom_shader.c
@@ -70,16 +70,13 @@ update_fp( struct st_context *st )
    key.clamp_color = st->clamp_frag_color_in_shader &&
                      st->ctx->Color._ClampFragmentColor;
 
-   /* Don't set it if the driver can force the interpolation by itself.
-    * If SAMPLE_ID or SAMPLE_POS are used, the interpolation is set
-    * automatically.
-    * Ignore sample qualifier while computing this flag.
-    */
+   /* _NEW_MULTISAMPLE | _NEW_BUFFERS */
    key.persample_shading =
       st->force_persample_in_shader &&
-      !(stfp->Base.Base.SystemValuesRead & (SYSTEM_BIT_SAMPLE_ID |
-                                            SYSTEM_BIT_SAMPLE_POS)) &&
-      _mesa_get_min_invocations_per_fragment(st->ctx, &stfp->Base, true) > 1;
+      ctx->Multisample._Enabled &&
+      ctx->Multisample.SampleShading &&
+      ctx->Multisample.MinSampleShadingValue *
+      _mesa_geometric_samples(ctx->DrawBuffer) > 1;
 
    st->fp_variant = st_get_fp_variant(st, stfp, &key);
 
diff --git a/src/mesa/state_tracker/st_program.c b/src/mesa/state_tracker/st_program.c
index 2e21d02..c9f390a 100644
--- a/src/mesa/state_tracker/st_program.c
+++ b/src/mesa/state_tracker/st_program.c
@@ -573,10 +573,6 @@ st_translate_fragment_program(struct st_context *st,
          else
             interpLocation[slot] = TGSI_INTERPOLATE_LOC_CENTER;
 
-         if (stfp->Base.Base.SystemValuesRead & (SYSTEM_BIT_SAMPLE_ID |
-                                                 SYSTEM_BIT_SAMPLE_POS))
-            interpLocation[slot] = TGSI_INTERPOLATE_LOC_SAMPLE;
-
          switch (attr) {
          case VARYING_SLOT_POS:
             input_semantic_name[slot] = TGSI_SEMANTIC_POSITION;
-- 
2.4.10