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gallivm: use correct rounding for nearest wrap mode (in the aos int path)

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The previous code used coords which were calculated as
(int) (f_coord * tex_size * 256) >> 8.
This is not only unnecessarily complex but can give the wrong texel due to
rounding for negative coords (as an example, after denormalization coords
from -1.0 to 0.0 should give -1, but this will give -1 for numbers from
-1.0-1/256 - 0.0-1/256.
Instead, juse use ifloor, dropping the shift stuff.
Unfortunately, this will most likely be slower - with arch rounding available
it shouldn't be too bad (trades a int shift for a round but also saves an int
mul (which is shared by all coords) but otherwise it's a mess.
This commit is contained in:
Roland Scheidegger
2014-02-15 03:45:00 +01:00
parent 88637e5764
commit 9954f01497
1 changed files with 9 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c
+9 -29
View File
@@ -567,10 +567,7 @@ lp_build_sample_image_nearest(struct lp_build_sample_context *bld,
LLVMValueRef *colors)
{
const unsigned dims = bld->dims;
LLVMBuilderRef builder = bld->gallivm->builder;
struct lp_build_context i32;
LLVMTypeRef i32_vec_type;
LLVMValueRef i32_c8;
LLVMValueRef width_vec, height_vec, depth_vec;
LLVMValueRef s_ipart, t_ipart = NULL, r_ipart = NULL;
LLVMValueRef s_float, t_float = NULL, r_float = NULL;
@@ -580,8 +577,6 @@ lp_build_sample_image_nearest(struct lp_build_sample_context *bld,
lp_build_context_init(&i32, bld->gallivm, lp_type_int_vec(32, bld->vector_width));
i32_vec_type = lp_build_vec_type(bld->gallivm, i32.type);
lp_build_extract_image_sizes(bld,
&bld->int_size_bld,
bld->int_coord_type,
@@ -593,39 +588,24 @@ lp_build_sample_image_nearest(struct lp_build_sample_context *bld,
s_float = s; t_float = t; r_float = r;
if (bld->static_sampler_state->normalized_coords) {
LLVMValueRef scaled_size;
LLVMValueRef flt_size;
/* scale size by 256 (8 fractional bits) */
scaled_size = lp_build_shl_imm(&bld->int_size_bld, int_size, 8);
flt_size = lp_build_int_to_float(&bld->float_size_bld, scaled_size);
flt_size = lp_build_int_to_float(&bld->float_size_bld, int_size);
lp_build_unnormalized_coords(bld, flt_size, &s, &t, &r);
}
else {
/* scale coords by 256 (8 fractional bits) */
s = lp_build_mul_imm(&bld->coord_bld, s, 256);
if (dims >= 2)
t = lp_build_mul_imm(&bld->coord_bld, t, 256);
if (dims >= 3)
r = lp_build_mul_imm(&bld->coord_bld, r, 256);
}
/* convert float to int */
s = LLVMBuildFPToSI(builder, s, i32_vec_type, "");
/* For correct rounding, need floor, not truncation here.
* Note that in some cases (clamp to edge, no texel offsets) we
* could use a non-signed build context which would help archs
* greatly which don't have arch rounding.
*/
s_ipart = lp_build_ifloor(&bld->coord_bld, s);
if (dims >= 2)
t = LLVMBuildFPToSI(builder, t, i32_vec_type, "");
t_ipart = lp_build_ifloor(&bld->coord_bld, t);
if (dims >= 3)
r = LLVMBuildFPToSI(builder, r, i32_vec_type, "");
/* compute floor (shift right 8) */
i32_c8 = lp_build_const_int_vec(bld->gallivm, i32.type, 8);
s_ipart = LLVMBuildAShr(builder, s, i32_c8, "");
if (dims >= 2)
t_ipart = LLVMBuildAShr(builder, t, i32_c8, "");
if (dims >= 3)
r_ipart = LLVMBuildAShr(builder, r, i32_c8, "");
r_ipart = lp_build_ifloor(&bld->coord_bld, r);
/* add texel offsets */
if (offsets[0]) {