softpipe: Add support for TGSI_OPCODE_INTERP_CENTROID

Like with interpolatAtSample this is also not really implementing the
according sampling and will only work correctly for pixels that are fully
covered, but since softpipe only supports one sample this is good enough
for now.

v2: Correct spelling (Roland Scheidegger)

Signed-off-by: Gert Wollny <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>

1 files changed, 42 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/tgsi/tgsi_exec.c b/src/gallium/auxiliary/tgsi/tgsi_exec.c
index 8fe46f780ab..34b72850208 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_exec.c
+++ b/src/gallium/auxiliary/tgsi/tgsi_exec.c
@@ -5234,6 +5234,45 @@ exec_interp_at_offset(struct tgsi_exec_machine *mach,
       store_dest(mach, &result, &inst->Dst[0], inst, chan, TGSI_EXEC_DATA_FLOAT);
    }
 }
+
+
+static void
+exec_interp_at_centroid(struct tgsi_exec_machine *mach,
+                        const struct tgsi_full_instruction *inst)
+{
+   union tgsi_exec_channel index;
+   union tgsi_exec_channel index2D;
+   union tgsi_exec_channel result[TGSI_NUM_CHANNELS];
+   const struct tgsi_full_src_register *reg = &inst->Src[0];
+
+   assert(reg->Register.File == TGSI_FILE_INPUT);
+   get_index_registers(mach, reg, &index, &index2D);
+
+   for (unsigned chan = 0; chan < TGSI_NUM_CHANNELS; chan++) {
+      if (!(inst->Dst[0].Register.WriteMask & (1 << chan)))
+         continue;
+
+      /* Here we should add the change to use a sample that lies within the
+       * primitive (Section 15.2):
+       *
+       * "When interpolating variables declared using centroid in ,
+       * the variable is sampled at a location within the pixel covered
+       * by the primitive generating the fragment.
+       * ...
+       * The built-in functions interpolateAtCentroid ... will sample
+       * variables as though they were declared with the centroid ...
+       * qualifier[s]."
+       *
+       * Since we only support 1 sample currently, this is just a pass-through.
+       */
+      fetch_src_file_channel(mach, TGSI_FILE_INPUT, chan, &index, &index2D,
+                             &result[chan]);
+      store_dest(mach, &result[chan], &inst->Dst[0], inst, chan, TGSI_EXEC_DATA_FLOAT);
+   }
+
+}
+
+
 /**
  * Execute a TGSI instruction.
  * Returns TRUE if a barrier instruction is hit,
@@ -6284,6 +6323,9 @@ exec_instruction(
    case TGSI_OPCODE_INTERP_OFFSET:
       exec_interp_at_offset(mach, inst);
       break;
+   case TGSI_OPCODE_INTERP_CENTROID:
+      exec_interp_at_centroid(mach, inst);
+      break;
    default:
       assert( 0 );
    }