Module: Mesa
Branch: master
Commit: 64c59b06244fc34f015f1f75b8205ac597ab0105
URL:    
http://cgit.freedesktop.org/mesa/mesa/commit/?id=64c59b06244fc34f015f1f75b8205ac597ab0105

Author: Roland Scheidegger <[email protected]>
Date:   Fri Dec 11 02:21:17 2015 +0100

draw: fix clipping with linear interpolated values and gl_ClipVertex

Discovered this when working on other clip code, apparently didn't work
correctly - the combination of linear interpolated values and using
gl_ClipVertex produced wrong values (failing all such combinations
in piglits glsl-1.30 interpolation tests, named
interpolation-noperspective-XXX-vertex).
Use the pre-clip-pos values when determining the interpolation factor to
fix this.
Noone really understands this code well, but everybody agrees this looks
sane... This fixes all those failing tests (10 in total) both with
the llvm and non-llvm draw paths, with no piglit regressions.

Reviewed-by: Brian Paul <[email protected]>
Reviewed-by: Dave Airlie <[email protected]>

---

 src/gallium/auxiliary/draw/draw_pipe_clip.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/gallium/auxiliary/draw/draw_pipe_clip.c 
b/src/gallium/auxiliary/draw/draw_pipe_clip.c
index 35e54f4..47765cd 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_clip.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_clip.c
@@ -192,11 +192,11 @@ static void interp(const struct clip_stage *clip,
       t_nopersp = t;
       /* find either in.x != out.x or in.y != out.y */
       for (k = 0; k < 2; k++) {
-         if (in->clip[k] != out->clip[k]) {
+         if (in->pre_clip_pos[k] != out->pre_clip_pos[k]) {
             /* do divide by W, then compute linear interpolation factor */
-            float in_coord = in->clip[k] / in->clip[3];
-            float out_coord = out->clip[k] / out->clip[3];
-            float dst_coord = dst->clip[k] / dst->clip[3];
+            float in_coord = in->pre_clip_pos[k] / in->pre_clip_pos[3];
+            float out_coord = out->pre_clip_pos[k] / out->pre_clip_pos[3];
+            float dst_coord = dst->pre_clip_pos[k] / dst->pre_clip_pos[3];
             t_nopersp = (dst_coord - out_coord) / (in_coord - out_coord);
             break;
          }

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