svga: avoid provoking vertex conversion when possible

Provoking vertex comes into play when doing flat shading.  But if we know
that all fragments in a primitive are the same color, the provoking vertex
doesn't matter.  Check for that case and use whichever provoking vertex
convention is supported by the device.

This avoids generating an index buffer to do the PV conversion.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Reviewed-by: José Fonseca <jfonseca@vmware.com>

diff --git a/src/gallium/drivers/svga/svga_draw_arrays.c b/src/gallium/drivers/svga/svga_draw_arrays.c
index 5635411..e4d7764 100644 (file)
--- a/src/gallium/drivers/svga/svga_draw_arrays.c
+++ b/src/gallium/drivers/svga/svga_draw_arrays.c
@@ -32,6 +32,7 @@
 #include "svga_draw.h"
 #include "svga_draw_private.h"
 #include "svga_context.h"
+#include "svga_shader.h"
 
 
 #define DBG 0
@@ -206,6 +207,18 @@ svga_hwtnl_draw_arrays(struct svga_hwtnl *hwtnl,
    unsigned gen_prim, gen_size, gen_nr, gen_type;
    u_generate_func gen_func;
    enum pipe_error ret = PIPE_OK;
+   unsigned api_pv = hwtnl->api_pv;
+   struct svga_context *svga = hwtnl->svga;
+
+   if (svga->curr.rast->templ.flatshade &&
+       svga->state.hw_draw.fs->constant_color_output) {
+      /* The fragment color is a constant, not per-vertex so the whole
+       * primitive will be the same color (except for possible blending).
+       * We can ignore the current provoking vertex state and use whatever
+       * the hardware wants.
+       */
+      api_pv = hwtnl->hw_pv;
+   }
 
    if (hwtnl->api_fillmode != PIPE_POLYGON_MODE_FILL &&
        prim >= PIPE_PRIM_TRIANGLES) {
@@ -226,7 +239,7 @@ svga_hwtnl_draw_arrays(struct svga_hwtnl *hwtnl,
                                    prim,
                                    start,
                                    count,
-                                   hwtnl->api_pv,
+                                   api_pv,
                                    hwtnl->hw_pv,
                                    &gen_prim, &gen_size, &gen_nr, &gen_func);
    }