On 10 December 2015 at 14:31, <srol...@vmware.com> wrote:
> From: Roland Scheidegger <srol...@vmware.com>
>
> 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).
> Use the pre-clip-pos values when determining the interpolation factor to
> fix this.
> Unfortunately I have no idea what I'm doing here really, but it fixes all
> these failures in piglit (all interpolation-noperspective-XXX-vertex, 10
> tests in total). Albeit piglit coverage of clipping isn't great, so hopefully
> someone can confirm this actually makes sense, and wouldn't cause failures
> elsewhere...
This makes sense to me, in that interpolating should definitely happen
on pre-clipped coordinates.
Though like you my knowledge of this code is debug only.
So,
Reviewed-by: Dave Airlie <airl...@redhat.com>
> ---
> 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 f2b56b0..7f22eef 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;
> }
> --
> 2.1.4
>
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