additional comments for tri_persp_coeff()

diff --git a/src/mesa/pipe/softpipe/sp_prim_setup.c b/src/mesa/pipe/softpipe/sp_prim_setup.c
index c64a4e970812e14a76698f5db7217e97216d690e..d0baf0734b01b55da25cabe4bd12cd6cf7c46f59 100644 (file)
--- a/src/mesa/pipe/softpipe/sp_prim_setup.c
+++ b/src/mesa/pipe/softpipe/sp_prim_setup.c
@@ -428,6 +428,10 @@ static void tri_linear_coeff( struct setup_stage *setup,
 /**
  * Compute a0, dadx and dady for a perspective-corrected interpolant,
  * for a triangle.
+ * We basically multiply the vertex value by 1/w before computing
+ * the plane coefficients (a0, dadx, dady).
+ * Later, when we compute the value at a particular fragment position we'll
+ * divide the interpolated value by the interpolated W at that fragment.
  */
 static void tri_persp_coeff( struct setup_stage *setup,
                              unsigned slot,