[Mesa-dev] [PATCH v2 2/2] indices: fix provoking vertex for quads/quadstrips

[Ilia Mirkin]

This allows drivers to provide consistent flat shading for quads.
Otherwise a driver that only supported tris would have to force last
provoking vertex when drawing quads (and would have to say that quads
don't follow the provoking vertex convention).

Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
---

vmware folks -- Please test this out with svga. I see that you might
have a similar issue with how you determine api_pv as
u_primconvert. Also if you don't expect quads to follow, you can
always just pass in pv == LAST, but then you still end up having to
force your rast state to pv = LAST too, for quads.

A good piglit to play with is:

  bin/arb-provoking-vertex-render

 src/gallium/auxiliary/indices/u_indices_gen.py | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/gallium/auxiliary/indices/u_indices_gen.py b/src/gallium/auxiliary/indices/u_indices_gen.py
index 687a717..97c8e0d 100644
--- a/src/gallium/auxiliary/indices/u_indices_gen.py
+++ b/src/gallium/auxiliary/indices/u_indices_gen.py
@@ -142,8 +142,12 @@ def do_tri( intype, outtype, ptr, v0, v1, v2, inpv, outpv ):
             tri( intype, outtype, ptr, v2, v0, v1 )
 
 def do_quad( intype, outtype, ptr, v0, v1, v2, v3, inpv, outpv ):
-    do_tri( intype, outtype, ptr+'+0',  v0, v1, v3, inpv, outpv );
-    do_tri( intype, outtype, ptr+'+3',  v1, v2, v3, inpv, outpv );
+    if inpv == LAST:
+        do_tri( intype, outtype, ptr+'+0',  v0, v1, v3, inpv, outpv );
+        do_tri( intype, outtype, ptr+'+3',  v1, v2, v3, inpv, outpv );
+    else:
+        do_tri( intype, outtype, ptr+'+0',  v0, v1, v2, inpv, outpv );
+        do_tri( intype, outtype, ptr+'+3',  v0, v2, v3, inpv, outpv );
 
 def name(intype, outtype, inpv, outpv, pr, prim):
     if intype == GENERATE:
@@ -331,7 +335,10 @@ def quadstrip(intype, outtype, inpv, outpv, pr):
         print '         i += 4;'
         print '         goto restart;'
         print '      }'
-    do_quad( intype, outtype, 'out+j', 'i+2', 'i+0', 'i+1', 'i+3', inpv, outpv );
+    if inpv == LAST:
+        do_quad( intype, outtype, 'out+j', 'i+2', 'i+0', 'i+1', 'i+3', inpv, outpv );
+    else:
+        do_quad( intype, outtype, 'out+j', 'i+0', 'i+1', 'i+3', 'i+2', inpv, outpv );
     print '   }'
     postamble()
 
-- 
2.0.5