draw: use position not clipVertex output for xyz view volume clipping

I'm pretty sure this should use position (i.e. pre_clip_pos) and not
the output from clipVertex. Albeit piglit doesn't care. It is what we
use in the clip test, and it is what every other driver does (as they
don't even have clipVertex output and lower the additional planes to
clip distances).

Reviewed-by: Brian Paul <brianp@vmware.com
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pipe_clip.c b/src/gallium/auxiliary/draw/draw_pipe_clip.c
index 47765cd..ae21be0 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_clip.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_clip.c
@@ -345,13 +345,22 @@ static inline float getclipdist(const struct clip_stage *clipper,
 {
    const float *plane;
    float dp;
-   if (vert->have_clipdist && plane_idx >= 6) {
+   if (plane_idx < 6) {
+      /* ordinary xyz view volume clipping uses pos output */
+      plane = clipper->plane[plane_idx];
+      dp = dot4(vert->pre_clip_pos, plane);
+   }
+   else if (vert->have_clipdist) {
       /* pick the correct clipdistance element from the output vectors */
       int _idx = plane_idx - 6;
       int cdi = _idx >= 4;
       int vidx = cdi ? _idx - 4 : _idx;
       dp = vert->data[draw_current_shader_clipdistance_output(clipper->stage.draw, cdi)][vidx];
    } else {
+      /*
+       * legacy user clip planes or gl_ClipVertex
+       * (clip will contain clipVertex output if available, pos otherwise).
+       */
       plane = clipper->plane[plane_idx];
       dp = dot4(vert->clip, plane);
    }