[Mesa-dev] [PATCH 05/18] i915: Handle provoking vertex in intelFastRenderClippedPoly()

[Ian Romanick]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

intelFastRenderClippedPoly() renders the polygon using triangles. For
polygons the provoking vertex is always the first one, and currently
this function assumes that the provoking vertex for triangles is the
last one. In case the user changed the provoking vertex convention,
the hardware may be configured to treat the first vertex of triangles
as the provoking vertex. So check the convention and emit the triangles
in the appropriate order to avoid having to change the hardware
provoking vertex convention for rendering polygons.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/mesa/drivers/dri/i915/intel_tris.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i915/intel_tris.c b/src/mesa/drivers/dri/i915/intel_tris.c
index ae62a80..828400c 100644
--- a/src/mesa/drivers/dri/i915/intel_tris.c
+++ b/src/mesa/drivers/dri/i915/intel_tris.c
@@ -928,10 +928,18 @@ intelFastRenderClippedPoly(struct gl_context * ctx, const GLuint * elts, GLuint
    const GLuint *start = (const GLuint *) V(elts[0]);
    int i, j;
 
-   for (i = 2; i < n; i++) {
-      COPY_DWORDS(j, vb, vertsize, V(elts[i - 1]));
-      COPY_DWORDS(j, vb, vertsize, V(elts[i]));
-      COPY_DWORDS(j, vb, vertsize, start);
+   if (ctx->Light.ProvokingVertex == GL_LAST_VERTEX_CONVENTION) {
+      for (i = 2; i < n; i++) {
+         COPY_DWORDS(j, vb, vertsize, V(elts[i - 1]));
+         COPY_DWORDS(j, vb, vertsize, V(elts[i]));
+         COPY_DWORDS(j, vb, vertsize, start);
+      }
+   } else {
+      for (i = 2; i < n; i++) {
+         COPY_DWORDS(j, vb, vertsize, start);
+         COPY_DWORDS(j, vb, vertsize, V(elts[i - 1]));
+         COPY_DWORDS(j, vb, vertsize, V(elts[i]));
+      }
    }
 }
 
-- 
2.1.0