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* Copyright 2023 Valve Corporation
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* Copyright 2023 Alyssa Rosenzweig
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* SPDX-License-Identifier: MIT
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#include "agx_tilebuffer.h"
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#include "nir_builder.h"
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mask_by_sample_id(nir_builder *b, nir_ssa_def *mask)
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nir_ssa_def *id_mask =
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nir_ishl(b, nir_imm_intN_t(b, 1, mask->bit_size), nir_load_sample_id(b));
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return nir_iand(b, mask, id_mask);
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lower_to_sample(nir_builder *b, nir_instr *instr, void *_)
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if (instr->type != nir_instr_type_intrinsic)
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nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
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b->cursor = nir_before_instr(instr);
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switch (intr->intrinsic) {
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case nir_intrinsic_load_sample_pos: {
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/* Lower sample positions to decode the packed fixed-point register:
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* uint32_t packed = load_sample_positions();
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* uint32_t shifted = packed >> (sample_id * 8);
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* for (i = 0; i < 2; ++i) {
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* uint8_t nibble = (shifted >> (i * 4)) & 0xF;
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* xy[component] = ((float)nibble) / 16.0;
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nir_ssa_def *packed = nir_load_sample_positions_agx(b);
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/* The n'th sample is the in the n'th byte of the register */
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nir_ssa_def *shifted = nir_ushr(
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b, packed, nir_u2u32(b, nir_imul_imm(b, nir_load_sample_id(b), 8)));
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for (unsigned i = 0; i < 2; ++i) {
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/* Get the appropriate nibble */
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nir_iand_imm(b, nir_ushr_imm(b, shifted, i * 4), 0xF);
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/* Convert it from fixed point to float */
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xy[i] = nir_fmul_imm(b, nir_u2f16(b, nibble), 1.0 / 16.0);
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/* Upconvert if necessary */
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xy[i] = nir_f2fN(b, xy[i], nir_dest_bit_size(intr->dest));
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/* Collect and rewrite */
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nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_vec2(b, xy[0], xy[1]));
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nir_instr_remove(instr);
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case nir_intrinsic_load_sample_mask_in: {
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/* In OpenGL, gl_SampleMaskIn is only supposed to have the single bit set
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* of the sample currently being shaded when sample shading is used. Mask
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* by the sample ID to make that happen.
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b->cursor = nir_after_instr(instr);
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nir_ssa_def *old = &intr->dest.ssa;
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nir_ssa_def *lowered = mask_by_sample_id(b, old);
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nir_ssa_def_rewrite_uses_after(old, lowered, lowered->parent_instr);
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case nir_intrinsic_load_barycentric_sample: {
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/* Lower fragment varyings with "sample" interpolation to
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* interpolateAtSample() with the sample ID
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b->cursor = nir_after_instr(instr);
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nir_ssa_def *old = &intr->dest.ssa;
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nir_ssa_def *lowered = nir_load_barycentric_at_sample(
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b, nir_dest_bit_size(intr->dest), nir_load_sample_id(b),
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.interp_mode = nir_intrinsic_interp_mode(intr));
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nir_ssa_def_rewrite_uses_after(old, lowered, lowered->parent_instr);
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* In a fragment shader using sample shading, lower intrinsics like
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* load_sample_position to variants in terms of load_sample_id. Except for a
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* possible API bit to force sample shading in shaders that don't otherwise need
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* it, this pass does not depend on the shader key. In particular, it does not
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* depend on the sample count. So it runs on fragment shaders at compile-time.
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* The load_sample_id intrinsics themselves are lowered later, with different
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* lowerings for monolithic vs epilogs.
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* Note that fragment I/O (like store_local_pixel_agx and discard_agx) does not
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* get lowered here, because that lowering is different for monolithic vs FS
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* epilogs even though there's no dependency on sample count.
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agx_nir_lower_sample_intrinsics(nir_shader *shader)
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/* If sample shading is disabled, the unlowered shader will broadcast pixel
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* values across the sample (the default). By definition, there are no sample
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* position or sample barycentrics, as these trigger sample shading.
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if (!shader->info.fs.uses_sample_shading)
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return nir_shader_instructions_pass(
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shader, lower_to_sample,
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nir_metadata_block_index | nir_metadata_dominance, NULL);
added
removed
src/asahi/lib/agx_nir_lower_sample_intrinsics.c
