softpipe: fix flat shading provoking vertex for PIPE_PRIM_POLYGON

Use the first vertex, not the last.

3 files changed, 6 insertions, 1 deletions

diff --git a/src/gallium/drivers/softpipe/sp_context.h b/src/gallium/drivers/softpipe/sp_context.h
index b89a7292e5..2f90d538a5 100644
--- a/src/gallium/drivers/softpipe/sp_context.h
+++ b/src/gallium/drivers/softpipe/sp_context.h
@@ -107,6 +107,7 @@ struct softpipe_context {
    /** Which vertex shader output slot contains point size */
    int psize_slot;
 
+   unsigned api_prim;  /**< current prim type being drawn: PIPE_PRIM_x */
    unsigned reduced_api_prim;  /**< PIPE_PRIM_POINTS, _LINES or _TRIANGLES */
 
    /** Derived from scissor and surface bounds: */
diff --git a/src/gallium/drivers/softpipe/sp_draw_arrays.c b/src/gallium/drivers/softpipe/sp_draw_arrays.c
index f117096bf7..1460bc4b4b 100644
--- a/src/gallium/drivers/softpipe/sp_draw_arrays.c
+++ b/src/gallium/drivers/softpipe/sp_draw_arrays.c
@@ -129,6 +129,7 @@ softpipe_draw_range_elements(struct pipe_context *pipe,
    struct draw_context *draw = sp->draw;
    unsigned i;
 
+   sp->api_prim = mode;
    sp->reduced_api_prim = reduced_prim[mode];
 
    if (sp->dirty)
diff --git a/src/gallium/drivers/softpipe/sp_setup.c b/src/gallium/drivers/softpipe/sp_setup.c
index accc692b66..c4dd61e41e 100644
--- a/src/gallium/drivers/softpipe/sp_setup.c
+++ b/src/gallium/drivers/softpipe/sp_setup.c
@@ -512,7 +512,10 @@ static boolean setup_sort_vertices( struct setup_context *setup,
                                     const float (*v1)[4],
                                     const float (*v2)[4] )
 {
-   setup->vprovoke = v2;
+   if (setup->softpipe->api_prim == PIPE_PRIM_POLYGON)
+      setup->vprovoke = v0;
+   else
+      setup->vprovoke = v2;
 
    /* determine bottom to top order of vertices */
    {