From f4ab1783b390cd8ff7f4b1e7ba9fc15893e2d69c Mon Sep 17 00:00:00 2001
From: Dave Airlie <airlied@redhat.com>
Date: Mon, 19 Dec 2011 15:57:50 +0000
Subject: [PATCH] gallium/draw: fix two side handling

The code didn't handle the case where front wasn't specified in the vertex
shader outputs, but back was.

In that case we were doing a copy from back to non-existant front,
this code checks we have existant front/backs and only does the copy when
they both exist.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
---
 .../auxiliary/draw/draw_pipe_twoside.c        | 27 +++++++------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/src/gallium/auxiliary/draw/draw_pipe_twoside.c b/src/gallium/auxiliary/draw/draw_pipe_twoside.c
index 9a3f3fee625..b1a70a02e47 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_twoside.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_twoside.c
@@ -38,8 +38,8 @@
 struct twoside_stage {
    struct draw_stage stage;
    float sign;         /**< +1 or -1 */
-   uint attrib_front0, attrib_back0;
-   uint attrib_front1, attrib_back1;
+   int attrib_front0, attrib_back0;
+   int attrib_front1, attrib_back1;
 };
 
 
@@ -48,9 +48,6 @@ static INLINE struct twoside_stage *twoside_stage( struct draw_stage *stage )
    return (struct twoside_stage *)stage;
 }
 
-
-
-
 /**
  * Copy back color(s) to front color(s).
  */
@@ -60,12 +57,12 @@ copy_bfc( struct twoside_stage *twoside,
           unsigned idx )
 {   
    struct vertex_header *tmp = dup_vert( &twoside->stage, v, idx );
-   
-   if (twoside->attrib_back0) {
+
+   if (twoside->attrib_back0 >= 0 && twoside->attrib_front0 >= 0) {
       COPY_4FV(tmp->data[twoside->attrib_front0],
                tmp->data[twoside->attrib_back0]);
    }
-   if (twoside->attrib_back1) {
+   if (twoside->attrib_back1 >= 0 && twoside->attrib_front1 >= 0) {
       COPY_4FV(tmp->data[twoside->attrib_front1],
                tmp->data[twoside->attrib_back1]);
    }
@@ -109,10 +106,10 @@ static void twoside_first_tri( struct draw_stage *stage,
    const struct draw_vertex_shader *vs = stage->draw->vs.vertex_shader;
    uint i;
 
-   twoside->attrib_front0 = 0;
-   twoside->attrib_front1 = 0;
-   twoside->attrib_back0 = 0;
-   twoside->attrib_back1 = 0;
+   twoside->attrib_front0 = -1;
+   twoside->attrib_front1 = -1;
+   twoside->attrib_back0 = -1;
+   twoside->attrib_back1 = -1;
 
    /* Find which vertex shader outputs are front/back colors */
    for (i = 0; i < vs->info.num_outputs; i++) {
@@ -130,12 +127,6 @@ static void twoside_first_tri( struct draw_stage *stage,
       }
    }
 
-   if (!twoside->attrib_back0)
-      twoside->attrib_front0 = 0;
-
-   if (!twoside->attrib_back1)
-      twoside->attrib_front1 = 0;
-
    /*
     * We'll multiply the primitive's determinant by this sign to determine
     * if the triangle is back-facing (negative).