gallium: rework provoking vertex code

Builds on commit ddb0e18f6c5582d4d2cc59ffd16ad9c4639ed059 and fixes
regressions in glean clipFlat test.

We assume that Gallium drivers observe flatshade_first for all triangles
and that all the assorted per-triangle calls in the 'draw' module also
follow flatshade_first.  Everything else builds on those rules.

Gallium does not use follow flatshade_first for GL quads, quad strips
and polygons; the "last" vertex is always the provoking vertex for those
prims.  So now there are separate QUAD_FIRST_PV and QUAD_LAST_PV macros
in the draw primitive decomposition code instead of one QUAD macro.

1 files changed, 22 insertions, 14 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pipe_clip.c b/src/gallium/auxiliary/draw/draw_pipe_clip.c
index 428ef4ef67..d0532cb341 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_clip.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_clip.c
@@ -164,10 +164,18 @@ static void emit_poly( struct draw_stage *stage,
 {
    struct prim_header header;
    unsigned i;
+   ushort edge_first, edge_middle, edge_last;
 
-   const ushort edge_first  = DRAW_PIPE_EDGE_FLAG_2;
-   const ushort edge_middle = DRAW_PIPE_EDGE_FLAG_0;
-   const ushort edge_last   = DRAW_PIPE_EDGE_FLAG_1;
+   if (stage->draw->rasterizer->flatshade_first) {
+      edge_first  = DRAW_PIPE_EDGE_FLAG_0;
+      edge_middle = DRAW_PIPE_EDGE_FLAG_1;
+      edge_last   = DRAW_PIPE_EDGE_FLAG_2;
+   }
+   else {
+      edge_first  = DRAW_PIPE_EDGE_FLAG_2;
+      edge_middle = DRAW_PIPE_EDGE_FLAG_0;
+      edge_last   = DRAW_PIPE_EDGE_FLAG_1;
+   }
 
    /* later stages may need the determinant, but only the sign matters */
    header.det = origPrim->det;
@@ -301,21 +309,21 @@ do_clip_tri( struct draw_stage *stage,
 
    /* If flat-shading, copy color to new provoking vertex.
     */
-   if (stage->draw->rasterizer->flatshade_first) {
-      if (clipper->flat && inlist[0] != header->v[0]) {
-         inlist[0] = dup_vert(stage, inlist[0], tmpnr++);
-
-         copy_colors(stage, inlist[0], header->v[0]);
+   if (clipper->flat) {
+      if (stage->draw->rasterizer->flatshade_first) {
+         if (inlist[0] != header->v[0]) {
+            inlist[0] = dup_vert(stage, inlist[0], tmpnr++);
+            copy_colors(stage, inlist[0], header->v[0]);
+         }
       }
-   } else {
-      if (clipper->flat && inlist[0] != header->v[2]) {
-         inlist[0] = dup_vert(stage, inlist[0], tmpnr++);
-
-         copy_colors(stage, inlist[0], header->v[2]);
+      else {
+         if (inlist[0] != header->v[2]) {
+            inlist[0] = dup_vert(stage, inlist[0], tmpnr++);
+            copy_colors(stage, inlist[0], header->v[2]);
+         }
       }
    }
 
-
    /* Emit the polygon as triangles to the setup stage:
     */
    if (n >= 3)