diff options
| -rw-r--r-- | src/mesa/drivers/dri/i965/brw_blorp_blit.cpp | 163 |
1 files changed, 145 insertions, 18 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp index 6c5a1e7229f..efca1b10ae8 100644 --- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp +++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp @@ -862,6 +862,133 @@ blorp_nir_decode_msaa(nir_builder *b, nir_ssa_def *pos, } /** + * Count the number of trailing 1 bits in the given value. For example: + * + * count_trailing_one_bits(0) == 0 + * count_trailing_one_bits(7) == 3 + * count_trailing_one_bits(11) == 2 + */ +static inline int count_trailing_one_bits(unsigned value) +{ +#ifdef HAVE___BUILTIN_CTZ + return __builtin_ctz(~value); +#else + return _mesa_bitcount(value & ~(value + 1)); +#endif +} + +static nir_ssa_def * +blorp_nir_manual_blend_average(nir_builder *b, nir_ssa_def *pos, + unsigned tex_samples, + enum intel_msaa_layout tex_layout, + enum brw_reg_type dst_type) +{ + /* If non-null, this is the outer-most if statement */ + nir_if *outer_if = NULL; + + nir_variable *color = + nir_local_variable_create(b->impl, glsl_vec4_type(), "color"); + + nir_ssa_def *mcs = NULL; + if (tex_layout == INTEL_MSAA_LAYOUT_CMS) + mcs = blorp_nir_txf_ms_mcs(b, pos); + + /* We add together samples using a binary tree structure, e.g. for 4x MSAA: + * + * result = ((sample[0] + sample[1]) + (sample[2] + sample[3])) / 4 + * + * This ensures that when all samples have the same value, no numerical + * precision is lost, since each addition operation always adds two equal + * values, and summing two equal floating point values does not lose + * precision. + * + * We perform this computation by treating the texture_data array as a + * stack and performing the following operations: + * + * - push sample 0 onto stack + * - push sample 1 onto stack + * - add top two stack entries + * - push sample 2 onto stack + * - push sample 3 onto stack + * - add top two stack entries + * - add top two stack entries + * - divide top stack entry by 4 + * + * Note that after pushing sample i onto the stack, the number of add + * operations we do is equal to the number of trailing 1 bits in i. This + * works provided the total number of samples is a power of two, which it + * always is for i965. + * + * For integer formats, we replace the add operations with average + * operations and skip the final division. + */ + nir_ssa_def *texture_data[4]; + unsigned stack_depth = 0; + for (unsigned i = 0; i < tex_samples; ++i) { + assert(stack_depth == _mesa_bitcount(i)); /* Loop invariant */ + + /* Push sample i onto the stack */ + assert(stack_depth < ARRAY_SIZE(texture_data)); + + nir_ssa_def *ms_pos = nir_vec3(b, nir_channel(b, pos, 0), + nir_channel(b, pos, 1), + nir_imm_int(b, i)); + texture_data[stack_depth++] = blorp_nir_txf_ms(b, ms_pos, mcs, dst_type); + + if (i == 0 && tex_layout == INTEL_MSAA_LAYOUT_CMS) { + /* The Ivy Bridge PRM, Vol4 Part1 p27 (Multisample Control Surface) + * suggests an optimization: + * + * "A simple optimization with probable large return in + * performance is to compare the MCS value to zero (indicating + * all samples are on sample slice 0), and sample only from + * sample slice 0 using ld2dss if MCS is zero." + * + * Note that in the case where the MCS value is zero, sampling from + * sample slice 0 using ld2dss and sampling from sample 0 using + * ld2dms are equivalent (since all samples are on sample slice 0). + * Since we have already sampled from sample 0, all we need to do is + * skip the remaining fetches and averaging if MCS is zero. + */ + nir_ssa_def *mcs_zero = + nir_ieq(b, nir_channel(b, mcs, 0), nir_imm_int(b, 0)); + nir_if *if_stmt = nir_if_create(b->shader); + if_stmt->condition = nir_src_for_ssa(mcs_zero); + nir_cf_node_insert(b->cursor, &if_stmt->cf_node); + + b->cursor = nir_after_cf_list(&if_stmt->then_list); + nir_store_var(b, color, texture_data[0], 0xf); + + b->cursor = nir_after_cf_list(&if_stmt->else_list); + outer_if = if_stmt; + } + + for (int j = 0; j < count_trailing_one_bits(i); j++) { + assert(stack_depth >= 2); + --stack_depth; + + assert(dst_type == BRW_REGISTER_TYPE_F); + texture_data[stack_depth - 1] = + nir_fadd(b, texture_data[stack_depth - 1], + texture_data[stack_depth]); + } + } + + /* We should have just 1 sample on the stack now. */ + assert(stack_depth == 1); + + texture_data[0] = nir_fmul(b, texture_data[0], + nir_imm_float(b, 1.0 / tex_samples)); + + nir_store_var(b, color, texture_data[0], 0xf); + + if (outer_if) + b->cursor = nir_after_cf_node(&outer_if->cf_node); + + return nir_load_var(b, color); +} + +/** * Generator for WM programs used in BLORP blits. * * The bulk of the work done by the WM program is to wrap and unwrap the @@ -1117,7 +1244,24 @@ brw_blorp_build_nir_shader(struct brw_context *brw, * irrelevant, because we are going to fetch all samples. */ if (key->blend && !key->blit_scaled) { - goto fail; + if (brw->gen == 6) { + /* Because gen6 only supports 4x interleved MSAA, we can do all the + * blending we need with a single linear-interpolated texture lookup + * at the center of the sample. The texture coordinates to be odd + * integers so that they correspond to the center of a 2x2 block + * representing the four samples that maxe up a pixel. So we need + * to multiply our X and Y coordinates each by 2 and then add 1. + */ + src_pos = nir_ishl(&b, src_pos, nir_imm_int(&b, 1)); + src_pos = nir_iadd(&b, src_pos, nir_imm_int(&b, 1)); + src_pos = nir_i2f(&b, nir_channels(&b, src_pos, 0x3)); + color = blorp_nir_tex(&b, src_pos, key->texture_data_type); + } else { + /* Gen7+ hardware doesn't automaticaly blend. */ + color = blorp_nir_manual_blend_average(&b, src_pos, key->src_samples, + key->src_layout, + key->texture_data_type); + } } else if (key->blend && key->blit_scaled) { goto fail; } else { @@ -2013,23 +2157,6 @@ brw_blorp_blit_program::clamp_tex_coords(struct brw_reg regX, -/** - * Count the number of trailing 1 bits in the given value. For example: - * - * count_trailing_one_bits(0) == 0 - * count_trailing_one_bits(7) == 3 - * count_trailing_one_bits(11) == 2 - */ -static inline int count_trailing_one_bits(unsigned value) -{ -#ifdef HAVE___BUILTIN_CTZ - return __builtin_ctz(~value); -#else - return _mesa_bitcount(value & ~(value + 1)); -#endif -} - - void brw_blorp_blit_program::manual_blend_average(unsigned num_samples) { |