[Mesa-dev] [PATCH] gallivm: drop border wrap clamping code

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

The border clamping code is unnecessary, since we don't care if a wrapped
coord value is -1 or <-1 (same for length vs. >length), in either case the
border handling code will mask out the offset and replace the texel value with
the border color.
Note that technically this is not entirely correct. Omitting clamping on the
float coords means that flt->int conversion may result in undefined values for
values of very large magnitude.
However there's no reason we should honor this here since:
a) we don't care for that for ordinary wrap modes in the aos code when
   converting coords and the problem is worse there (as we've got only
   effectively 24 instead of 32bits)
b) at least in some cases the clamping was done already in int space hence
   doing nothing to fix that problem.
c) with sse2 flt->int conversion with such values results in 0x80000000 which
   is just perfect (for clamp to border - not so much for the ordinary clamp to
   edge).
---
 src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c |   49 +++++++--------------
 1 file changed, 16 insertions(+), 33 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
index 659de9b..ba265b2 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
@@ -351,20 +351,16 @@ lp_build_sample_wrap_linear(struct lp_build_sample_context *bld,
       }
 
    case PIPE_TEX_WRAP_CLAMP_TO_BORDER:
-      {
-         LLVMValueRef min;
-         if (bld->static_state->normalized_coords) {
-            /* scale coord to length */
-            coord = lp_build_mul(coord_bld, coord, length_f);
-         }
-         /* was: clamp to [-0.5, length + 0.5], then sub 0.5 */
-         coord = lp_build_sub(coord_bld, coord, half);
-         min = lp_build_const_vec(bld->gallivm, coord_bld->type, -1.0F);
-         coord = lp_build_clamp(coord_bld, coord, min, length_f);
-         /* convert to int, compute lerp weight */
-         lp_build_ifloor_fract(coord_bld, coord, &coord0, &weight);
-         coord1 = lp_build_add(int_coord_bld, coord0, int_coord_bld->one);
+      if (bld->static_state->normalized_coords) {
+         /* scale coord to length */
+         coord = lp_build_mul(coord_bld, coord, length_f);
       }
+      /* was: clamp to [-0.5, length + 0.5], then sub 0.5 */
+      /* can skip clamp (though might not work for very large coord values */
+      coord = lp_build_sub(coord_bld, coord, half);
+      /* convert to int, compute lerp weight */
+      lp_build_ifloor_fract(coord_bld, coord, &coord0, &weight);
+      coord1 = lp_build_add(int_coord_bld, coord0, int_coord_bld->one);
       break;
 
    case PIPE_TEX_WRAP_MIRROR_REPEAT:
@@ -438,9 +434,9 @@ lp_build_sample_wrap_linear(struct lp_build_sample_context *bld,
          }
 
          /* was: clamp to [-0.5, length + 0.5] then sub 0.5 */
-         /* skip -0.5 clamp (always positive), do sub first */
+         /* skip clamp - always positive, and other side
+            only potentially matters for very large coords */
          coord = lp_build_sub(coord_bld, coord, half);
-         coord = lp_build_min(coord_bld, coord, length_f);
 
          /* convert to int, compute lerp weight */
          lp_build_ifloor_fract(coord_bld, coord, &coord0, &weight);
@@ -514,22 +510,12 @@ lp_build_sample_wrap_nearest(struct lp_build_sample_context *bld,
       break;
 
    case PIPE_TEX_WRAP_CLAMP_TO_BORDER:
-      /* Note: this is the same as CLAMP_TO_EDGE, except min = -1 */
-      {
-         LLVMValueRef min, max;
-
-         if (bld->static_state->normalized_coords) {
-            /* scale coord to length */
-            coord = lp_build_mul(coord_bld, coord, length_f);
-         }
-
-         icoord = lp_build_ifloor(coord_bld, coord);
-
-         /* clamp to [-1, length] */
-         min = lp_build_negate(int_coord_bld, int_coord_bld->one);
-         max = length;
-         icoord = lp_build_clamp(int_coord_bld, icoord, min, max);
+      if (bld->static_state->normalized_coords) {
+         /* scale coord to length */
+         coord = lp_build_mul(coord_bld, coord, length_f);
       }
+      /* no clamp necessary, border masking will handle this */
+      icoord = lp_build_ifloor(coord_bld, coord);
       break;
 
    case PIPE_TEX_WRAP_MIRROR_REPEAT:
@@ -573,9 +559,6 @@ lp_build_sample_wrap_nearest(struct lp_build_sample_context *bld,
 
       /* itrunc == ifloor here */
       icoord = lp_build_itrunc(coord_bld, coord);
-
-      /* clamp to [0, length] */
-      icoord = lp_build_min(int_coord_bld, icoord, length);
       break;
 
    default:
-- 
1.7.9.5