[Mesa-dev] [PATCH 3/4] gallivm: fix sampling with texture offsets in SoA path

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

When using nearest filtering and clamp / clamp to edge wrapping results could
be wrong for negative offsets. Fix this by adding the offset before doing
the conversion to int coords (could also use floor instead of trunc int
conversion but probably more complex on "typical" cpu).

This fixes the piglit texwrap offset failures with this filter/wrap combo
(which only leaves the linear/mirror repeat combination broken).
---
 src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
index b5c06b6..125505e 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
@@ -567,12 +567,13 @@ lp_build_sample_wrap_nearest(struct lp_build_sample_context *bld,
          coord = lp_build_mul(coord_bld, coord, length_f);
       }
 
+      if (offset) {
+         offset = lp_build_int_to_float(coord_bld, offset);
+         coord = lp_build_add(coord_bld, coord, offset);
+      }
       /* floor */
       /* use itrunc instead since we clamp to 0 anyway */
       icoord = lp_build_itrunc(coord_bld, coord);
-      if (offset) {
-         icoord = lp_build_add(int_coord_bld, icoord, offset);
-      }
 
       /* clamp to [0, length - 1]. */
       icoord = lp_build_clamp(int_coord_bld, icoord, int_coord_bld->zero,
@@ -2586,6 +2587,10 @@ lp_build_sample_soa_code(struct gallivm_state *gallivm,
       derived_sampler_state.wrap_s = PIPE_TEX_WRAP_CLAMP_TO_EDGE;
       derived_sampler_state.wrap_t = PIPE_TEX_WRAP_CLAMP_TO_EDGE;
    }
+   /*
+    * We could force CLAMP to CLAMP_TO_EDGE here if min/mag filter is nearest,
+    * so AoS path could be used. Not sure it's worth the trouble...
+    */
 
    min_img_filter = derived_sampler_state.min_img_filter;
    mag_img_filter = derived_sampler_state.mag_img_filter;
-- 
2.1.4