draw: fix problem in screen-space interpolation clip code
I don't see how this could have ever worked right.
The screen-space interpolation code uses the vertex->data[pos_attr]
position which contain window coords. But window coords are only
computed for the unclipped vertices; the clipped vertices have
undefined window coords (see draw_cliptest_tmp.h).
Use the vertex clip coords instead which are always defined.
Fixes http://bugs.freedesktop.org/show_bug.cgi?id=55476
(piglit fbo-blit-stretch failure on softpipe)
Note: This is a candidate for the 9.0 branch.
Reviewed-by: José Fonseca <jfonseca@vmware.com>
diff --git a/src/gallium/auxiliary/draw/draw_pipe_clip.c b/src/gallium/auxiliary/draw/draw_pipe_clip.c
index 878d779..7b879c4 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_clip.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_clip.c
@@ -168,9 +168,9 @@
int k;
t_nopersp = t;
for (k = 0; k < 2; k++)
- if (in->data[pos_attr][k] != out->data[pos_attr][k]) {
- t_nopersp = (dst->data[pos_attr][k] - out->data[pos_attr][k]) /
- (in->data[pos_attr][k] - out->data[pos_attr][k]);
+ if (in->clip[k] != out->clip[k]) {
+ t_nopersp = (dst->clip[k] - out->clip[k]) /
+ (in->clip[k] - out->clip[k]);
break;
}
}