1 /*
2 * Copyright © 2017 Broadcom
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 /**
25 * @file
26 *
27 * Implements GL alpha testing by comparing the output color's alpha to the
28 * alpha_ref intrinsic and emitting a discard based on it.
29 *
30 * The alpha_to_one value overrides the source alpha to 1.0 to implement
31 * GL_SAMPLE_ALPHA_TO_ONE, which applies before the alpha test (and would be
32 * rather silly to use with alpha test, but the spec permits).
33 */
34
35 #include "nir/nir.h"
36 #include "nir/nir_builder.h"
37
38 void
nir_lower_alpha_test(nir_shader * shader,enum compare_func func,bool alpha_to_one)39 nir_lower_alpha_test(nir_shader *shader, enum compare_func func,
40 bool alpha_to_one)
41 {
42 assert(shader->info.stage == MESA_SHADER_FRAGMENT);
43
44 nir_foreach_function(function, shader) {
45 nir_function_impl *impl = function->impl;
46 nir_builder b;
47 nir_builder_init(&b, impl);
48 b.cursor = nir_before_cf_list(&impl->body);
49
50 nir_foreach_block(block, impl) {
51 nir_foreach_instr_safe(instr, block) {
52 if (instr->type == nir_instr_type_intrinsic) {
53 nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
54
55 nir_variable *out = NULL;
56
57 switch (intr->intrinsic) {
58 case nir_intrinsic_store_var:
59 out = intr->variables[0]->var;
60 break;
61 case nir_intrinsic_store_output:
62 /* already had i/o lowered.. lookup the matching output var: */
63 nir_foreach_variable(var, &shader->outputs) {
64 int drvloc = var->data.driver_location;
65 if (nir_intrinsic_base(intr) == drvloc) {
66 out = var;
67 break;
68 }
69 }
70 assume(out);
71 break;
72 default:
73 continue;
74 }
75
76 if (out->data.mode != nir_var_shader_out)
77 continue;
78
79 if (out->data.location != FRAG_RESULT_COLOR &&
80 out->data.location != FRAG_RESULT_DATA0)
81 continue;
82
83 b.cursor = nir_before_instr(&intr->instr);
84
85 nir_ssa_def *alpha;
86 if (alpha_to_one) {
87 alpha = nir_imm_float(&b, 1.0);
88 } else {
89 alpha = nir_channel(&b, nir_ssa_for_src(&b, intr->src[0], 4),
90 3);
91 }
92
93 nir_ssa_def *condition =
94 nir_compare_func(&b, func,
95 alpha, nir_load_alpha_ref_float(&b));
96
97 nir_intrinsic_instr *discard =
98 nir_intrinsic_instr_create(b.shader,
99 nir_intrinsic_discard_if);
100 discard->num_components = 1;
101 discard->src[0] = nir_src_for_ssa(nir_inot(&b, condition));
102 nir_builder_instr_insert(&b, &discard->instr);
103 shader->info.fs.uses_discard = true;
104 }
105 }
106 }
107
108 nir_metadata_preserve(impl, nir_metadata_block_index |
109 nir_metadata_dominance);
110 }
111 }
112