test against -1 for front/back attrib

diff --git a/src/mesa/pipe/draw/draw_twoside.c b/src/mesa/pipe/draw/draw_twoside.c
index 9547f2a..26d26e6 100644 (file)
--- a/src/mesa/pipe/draw/draw_twoside.c
+++ b/src/mesa/pipe/draw/draw_twoside.c
@@ -78,12 +78,12 @@ static struct vertex_header *copy_bfc( struct twoside_stage *twoside,
    struct vertex_header *tmp = dup_vert( &twoside->stage, v, idx );
    const struct draw_context *draw = twoside->stage.draw;
    
-   if (draw->attrib_front0) {
-      assert(draw->attrib_back0);
+   if (draw->attrib_front0 != -1) {
+      assert(draw->attrib_back0 != -1);
       copy_attrib(draw->attrib_front0, draw->attrib_back0, tmp);
    }
-   if (draw->attrib_front1) {
-      assert(draw->attrib_back1);
+   if (draw->attrib_front1 != -1) {
+      assert(draw->attrib_back1 != -1);
       copy_attrib(draw->attrib_front1, draw->attrib_back1, tmp);
    }