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-rw-r--r--src/mesa/pipe/softpipe/sp_prim_setup.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/src/mesa/pipe/softpipe/sp_prim_setup.c b/src/mesa/pipe/softpipe/sp_prim_setup.c
index c64a4e97081..d0baf0734b0 100644
--- 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,