remove unneeded casts, added comments

src/mesa/pipe/draw/draw_cull.c

@@ -64,19 +64,19 @@ static void cull_tri( struct prim_stage *stage,
 		      struct prim_header *header )
 {
    /* Window coords: */
-   GLfloat *v0 = (GLfloat *)&(header->v[0]->data[0]);
-   GLfloat *v1 = (GLfloat *)&(header->v[1]->data[0]);
-   GLfloat *v2 = (GLfloat *)&(header->v[2]->data[0]);
+   const GLfloat *v0 = header->v[0]->data[0];
+   const GLfloat *v1 = header->v[1]->data[0];
+   const GLfloat *v2 = header->v[2]->data[0];
 
+   /* edge vectors e = v0 - v2, f = v1 - v2 */
    GLfloat ex = v0[0] - v2[0];
    GLfloat ey = v0[1] - v2[1];
    GLfloat fx = v1[0] - v2[0];
    GLfloat fy = v1[1] - v2[1];
    
+   /* det = cross(e,f).z */
    header->det = ex * fy - ey * fx;
 
-   _mesa_printf("%s %f\n", __FUNCTION__, header->det );
-
    if (header->det != 0) {
       /* non-zero area */
       GLuint mode = (header->det < 0) ? PIPE_WINDING_CW : PIPE_WINDING_CCW;