1 /*
2 * Copyright © 2022 Advanced Micro Devices, Inc.
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 */
23
24 #include "nir.h"
25 #include "nir_builder.h"
26 #include "nir_builtin_builder.h"
27
28 /**
29 * This NIR lowers pass for point smoothing by modifying the alpha value of
30 * fragment outputs using the distance from the center of the point.
31 * Anti-aliased points get rounded with respect to their radius.
32 */
33
34 static bool
lower_point_smooth(nir_builder *b, nir_instr *instr, UNUSED void *_state)35 lower_point_smooth(nir_builder *b, nir_instr *instr, UNUSED void *_state)
36 {
37 if (instr->type != nir_instr_type_intrinsic)
38 return false;
39
40 nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
41
42 if (intr->intrinsic != nir_intrinsic_store_output)
43 return false;
44
45 int location = nir_intrinsic_io_semantics(intr).location;
46 if ((location != FRAG_RESULT_COLOR && location < FRAG_RESULT_DATA0) ||
47 nir_intrinsic_src_type(intr) != nir_type_float32)
48 return false;
49
50 assert(intr->src[0].is_ssa);
51 assert(intr->num_components == 4);
52
53 b->cursor = nir_before_instr(&intr->instr);
54
55 nir_ssa_def *coord = nir_build_load_point_coord_maybe_flipped(b);
56
57 /* point_size = 1.0 / dFdx(gl_PointCoord.x); */
58 nir_ssa_def *point_size = nir_frcp(b, nir_fddx(b, nir_channel(b, coord, 0)));
59
60 /* radius = point_size * 0.5 */
61 nir_ssa_def *radius = nir_fmul_imm(b, point_size, 0.5);;
62
63 /**
64 * Compute the distance of point from centre
65 * distance = √ (x - 0.5)^2 + (y - 0.5)^2
66 */
67 nir_ssa_def *distance = nir_fast_distance(b, coord,
68 nir_imm_vec2(b, 0.5, 0.5));
69 distance = nir_fmul(b, distance, point_size);
70
71 /* alpha = min(max(radius - distance, 0.0), 1.0) */
72 nir_ssa_def *coverage = nir_fsat(b, nir_fsub(b, radius, distance));
73
74 /* Discard fragments that are not covered by the point */
75 nir_discard_if(b, nir_feq(b, nir_imm_float(b, 0.0f), coverage));
76
77 /* Write out the fragment color*vec4(1, 1, 1, coverage)*/
78 nir_ssa_def *one = nir_imm_float(b, 1.0f);
79 nir_ssa_def *new_val = nir_fmul(b, nir_vec4(b, one, one, one, coverage),
80 intr->src[0].ssa);
81 nir_instr_rewrite_src(instr, &intr->src[0], nir_src_for_ssa(new_val));
82
83 return true;
84 }
85
86 bool
nir_lower_point_smooth(nir_shader *shader)87 nir_lower_point_smooth(nir_shader *shader)
88 {
89 assert(shader->info.stage == MESA_SHADER_FRAGMENT);
90 return nir_shader_instructions_pass(shader, lower_point_smooth,
91 nir_metadata_loop_analysis |
92 nir_metadata_block_index |
93 nir_metadata_dominance, NULL);
94 }
95