Am 15.02.2014 01:54, schrieb srol...@vmware.com: > From: Jeff Muizelaar <jmuizel...@mozilla.com> > > The previous method for converting coords to ints was sligthly inaccurate > (effectively losing 1bit from the 8bit lerp weight). This is probably > especially noticeable when trying to draw a pixel-aligned texture. > As an example, for a 100x100 texture after dernormalization the texture > coords in this case would turn up as > 0.5, 1.5, 2.5, 3.5, 4.5, ... > After the mul by 256, conversion to int and 128 subtraction, they end up as > 0, 256, 512, 768, 1024, ... > which gets us the correct coords/weights of > 0/0, 1/0, 2/0, 3/0, 4/0, ... > But even LSB errors (which are unavoidable) in the input coords may cause > these coords/weights to be wrong, e.g. for a coord of 3.49999 we'd get a > coord/weight of 2/255 instead. > > Fix this by using round-to-nearest int instead of FPToSi (trunc). Should be > equally fast on x86 sse though other archs probably suffer a little. > --- > src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c > b/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c > index c35b628..1d87ee8 100644 > --- a/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c > +++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c > @@ -987,7 +987,6 @@ lp_build_sample_image_linear(struct > lp_build_sample_context *bld, > const unsigned dims = bld->dims; > LLVMBuilderRef builder = bld->gallivm->builder; > struct lp_build_context i32; > - LLVMTypeRef i32_vec_type; > LLVMValueRef i32_c8, i32_c128, i32_c255; > LLVMValueRef width_vec, height_vec, depth_vec; > LLVMValueRef s_ipart, s_fpart, s_float; > @@ -1003,8 +1002,6 @@ lp_build_sample_image_linear(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, > @@ -1036,11 +1033,16 @@ lp_build_sample_image_linear(struct > lp_build_sample_context *bld, > } > > /* convert float to int */ > - s = LLVMBuildFPToSI(builder, s, i32_vec_type, ""); > + /* For correct rounding, need round to nearest, 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 which > + * don't have fptosi intrinsic with nearest rounding implemented. > + */ > + s_ipart = lp_build_iround(&bld->coord_bld, s); > if (dims >= 2) > - t = LLVMBuildFPToSI(builder, t, i32_vec_type, ""); > + t_ipart = lp_build_iround(&bld->coord_bld, t); > if (dims >= 3) > - r = LLVMBuildFPToSI(builder, r, i32_vec_type, ""); > + r_ipart = lp_build_iround(&bld->coord_bld, r); > > /* subtract 0.5 (add -128) */ > i32_c128 = lp_build_const_int_vec(bld->gallivm, i32.type, -128); >
Oops this series is quite a disaster, sorry. That should have been s_ipart/t_ipart/r_ipart above of course, my typo... And 2/3 is quite fail too with some nice texel shift, bad math there... 3/3 may be ok... Roland _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
