Previously, we computed dFdy() using the following instruction: add(8) dst<1>F src<4,4,0)F -src.2<4,4,0>F { align1 1Q }
That had the disadvantage that it computed the same value for all 4 pixels of a 2x2 subspan, which meant that it was less accurate than dFdx(). This patch changes it to the following instruction when c->key.high_quality_derivatives is set: add(8) dst<1>F src<4,4,1>.xyxyF -src<4,4,1>.zwzwF { align16 1Q } This gives it comparable accuracy to dFdx(). Unfortunately, for some reason the SIMD16 version of this instruction: add(16) dst<1>F src<4,4,1>.xyxyF -src<4,4,1>.zwzwF { align16 1H } Doesn't seem to work reliably (presumably the hardware designers never validated the combination of align16 mode with compressed instructions), so we unroll it to: add(8) dst<1>F src<4,4,1>.xyxyF -src<4,4,1>.zwzwF { align16 1Q } add(8) (dst+1)<1>F (src+1)<4,4,1>.xyxyF -(src+1)<4,4,1>.zwzwF { align16 2Q } Fixes piglit test spec/glsl-1.10/execution/fs-dfdy-accuracy. --- Note: this patch needs to be applied atop Chia-I Wu's "i965: compute DDX in a subspan based only on top row" (http://lists.freedesktop.org/archives/mesa-dev/2013-September/045544.html). src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 77 +++++++++++++++++++------- src/mesa/drivers/dri/i965/brw_reg.h | 1 + 2 files changed, 58 insertions(+), 20 deletions(-) diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp index 9eb5e17..4efedc57 100644 --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp @@ -560,10 +560,8 @@ fs_generator::generate_tex(fs_inst *inst, struct brw_reg dst, struct brw_reg src * sample_d. On at least Haswell, sample_d instruction does some * optimizations if the same LOD is used for all pixels in the subspan. * - * For DDY, it's harder, as we want to produce the pairs swizzled between each - * other. We could probably do it like ddx and swizzle the right order later, - * but bail for now and just produce - * ((ss0.tl - ss0.bl)x4 (ss1.tl - ss1.bl)x4) + * For DDY, we need to use ALIGN16 mode since it's capable of doing the + * appropriate swizzling. */ void fs_generator::generate_ddx(fs_inst *inst, struct brw_reg dst, struct brw_reg src) @@ -604,22 +602,61 @@ void fs_generator::generate_ddy(fs_inst *inst, struct brw_reg dst, struct brw_reg src, bool negate_value) { - struct brw_reg src0 = brw_reg(src.file, src.nr, 0, - BRW_REGISTER_TYPE_F, - BRW_VERTICAL_STRIDE_4, - BRW_WIDTH_4, - BRW_HORIZONTAL_STRIDE_0, - BRW_SWIZZLE_XYZW, WRITEMASK_XYZW); - struct brw_reg src1 = brw_reg(src.file, src.nr, 2, - BRW_REGISTER_TYPE_F, - BRW_VERTICAL_STRIDE_4, - BRW_WIDTH_4, - BRW_HORIZONTAL_STRIDE_0, - BRW_SWIZZLE_XYZW, WRITEMASK_XYZW); - if (negate_value) - brw_ADD(p, dst, src1, negate(src0)); - else - brw_ADD(p, dst, src0, negate(src1)); + if (c->key.high_quality_derivatives) { + /* produce accurate derivatives */ + struct brw_reg src0 = brw_reg(src.file, src.nr, 0, + BRW_REGISTER_TYPE_F, + BRW_VERTICAL_STRIDE_4, + BRW_WIDTH_4, + BRW_HORIZONTAL_STRIDE_1, + BRW_SWIZZLE_XYXY, WRITEMASK_XYZW); + struct brw_reg src1 = brw_reg(src.file, src.nr, 0, + BRW_REGISTER_TYPE_F, + BRW_VERTICAL_STRIDE_4, + BRW_WIDTH_4, + BRW_HORIZONTAL_STRIDE_1, + BRW_SWIZZLE_ZWZW, WRITEMASK_XYZW); + brw_push_insn_state(p); + brw_set_access_mode(p, BRW_ALIGN_16); + brw_set_compression_control(p, BRW_COMPRESSION_NONE); + if (negate_value) + brw_ADD(p, dst, src1, negate(src0)); + else + brw_ADD(p, dst, src0, negate(src1)); + if (dispatch_width == 16) { + /* For some reason, instruction compression doesn't seem to work + * properly with ALIGN16 mode, so when doing a 16-wide dispatch, just + * manually unroll to two instructions. + */ + brw_set_compression_control(p, BRW_COMPRESSION_2NDHALF); + src0 = sechalf(src0); + src1 = sechalf(src1); + dst = sechalf(dst); + if (negate_value) + brw_ADD(p, dst, src1, negate(src0)); + else + brw_ADD(p, dst, src0, negate(src1)); + } + brw_pop_insn_state(p); + } else { + /* replicate the derivative at the top-left pixel to other pixels */ + struct brw_reg src0 = brw_reg(src.file, src.nr, 0, + BRW_REGISTER_TYPE_F, + BRW_VERTICAL_STRIDE_4, + BRW_WIDTH_4, + BRW_HORIZONTAL_STRIDE_0, + BRW_SWIZZLE_XYZW, WRITEMASK_XYZW); + struct brw_reg src1 = brw_reg(src.file, src.nr, 2, + BRW_REGISTER_TYPE_F, + BRW_VERTICAL_STRIDE_4, + BRW_WIDTH_4, + BRW_HORIZONTAL_STRIDE_0, + BRW_SWIZZLE_XYZW, WRITEMASK_XYZW); + if (negate_value) + brw_ADD(p, dst, src1, negate(src0)); + else + brw_ADD(p, dst, src0, negate(src1)); + } } void diff --git a/src/mesa/drivers/dri/i965/brw_reg.h b/src/mesa/drivers/dri/i965/brw_reg.h index 6df3366..3ee3543 100644 --- a/src/mesa/drivers/dri/i965/brw_reg.h +++ b/src/mesa/drivers/dri/i965/brw_reg.h @@ -77,6 +77,7 @@ extern "C" { #define BRW_SWIZZLE_ZZZZ BRW_SWIZZLE4(2,2,2,2) #define BRW_SWIZZLE_WWWW BRW_SWIZZLE4(3,3,3,3) #define BRW_SWIZZLE_XYXY BRW_SWIZZLE4(0,1,0,1) +#define BRW_SWIZZLE_ZWZW BRW_SWIZZLE4(2,3,2,3) static inline bool brw_is_single_value_swizzle(int swiz) -- 1.8.4 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev