Remove dependency on TGSI_ATTRIB_x tokens in draw_twoside.c

Added a new draw_set_twoside_attributes() function for specifying which
vertex attributes are to be copied/replaced when a polygon is back-facing.

1 files changed, 41 insertions, 0 deletions

diff --git a/src/mesa/pipe/draw/draw_context.c b/src/mesa/pipe/draw/draw_context.c
index b14de34141..c15f7652a6 100644
--- a/src/mesa/pipe/draw/draw_context.c
+++ b/src/mesa/pipe/draw/draw_context.c
@@ -67,6 +67,11 @@ struct draw_context *draw_create( void )
 	 draw->vcache.vertex[i] = (struct vertex_header *)(tmp + i * MAX_VERTEX_SIZE);
    }
 
+   draw->attrib_front0 = -1;
+   draw->attrib_back0 = -1;
+   draw->attrib_front1 = -1;
+   draw->attrib_back1 = -1;
+
    return draw;
 }
 
@@ -210,3 +215,39 @@ draw_set_vertex_shader(struct draw_context *draw,
 {
    draw->vertex_shader = *shader;
 }
+
+
+/**
+ * This function is used to tell the draw module about attributes
+ * (like colors) that need to be selected based on front/back face
+ * orientation.
+ *
+ * The logic is:
+ *    if (polygon is back-facing) {
+ *       vertex->attrib[front0] = vertex->attrib[back0];
+ *       vertex->attrib[front1] = vertex->attrib[back1];
+ *    }
+ *
+ * \param front0  first attrib to replace if the polygon is back-facing
+ * \param back0  first attrib to copy if the polygon is back-facing
+ * \param front1  second attrib to replace if the polygon is back-facing
+ * \param back1  second attrib to copy if the polygon is back-facing
+ *
+ * Pass -1 to disable two-sided attributes.
+ */
+void
+draw_set_twoside_attributes(struct draw_context *draw,
+                            uint front0, uint back0,
+                            uint front1, uint back1)
+{
+   /* XXX we could alternately pass an array of front/back attribs if there's
+    * ever need for more than two.  One could imagine a shader extension
+    * that allows arbitrary attributes to be selected based on polygon
+    * orientation...
+    */
+   draw->attrib_front0 = front0;
+   draw->attrib_back0 = back0;
+   draw->attrib_front1 = front1;
+   draw->attrib_back1 = back1;
+}
+