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
38void
39nir_lower_alpha_test(nir_shader *shader, enum compare_func func,
40                     bool alpha_to_one,
41                     const gl_state_index16 *alpha_ref_state_tokens)
42{
43   assert(alpha_ref_state_tokens);
44   assert(shader->info.stage == MESA_SHADER_FRAGMENT);
45
46   nir_foreach_function(function, shader) {
47      nir_function_impl *impl = function->impl;
48      nir_builder b;
49      nir_builder_init(&b, impl);
50      b.cursor = nir_before_cf_list(&impl->body);
51
52      nir_foreach_block(block, impl) {
53         nir_foreach_instr_safe(instr, block) {
54            if (instr->type == nir_instr_type_intrinsic) {
55               nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
56
57               nir_variable *out = NULL;
58
59               switch (intr->intrinsic) {
60               case nir_intrinsic_store_deref:
61                  out = nir_deref_instr_get_variable(nir_src_as_deref(intr->src[0]));
62                  break;
63               case nir_intrinsic_store_output:
64                  /* already had i/o lowered.. lookup the matching output var: */
65                  nir_foreach_shader_out_variable(var, shader) {
66                     int drvloc = var->data.driver_location;
67                     if (nir_intrinsic_base(intr) == drvloc) {
68                        out = var;
69                        break;
70                     }
71                  }
72                  assume(out);
73                  break;
74               default:
75                  continue;
76               }
77
78               if (out->data.mode != nir_var_shader_out)
79                  continue;
80
81               if (out->data.location != FRAG_RESULT_COLOR &&
82                   out->data.location != FRAG_RESULT_DATA0)
83                  continue;
84
85               b.cursor = nir_before_instr(&intr->instr);
86
87               nir_ssa_def *alpha;
88               if (alpha_to_one) {
89                  alpha = nir_imm_float(&b, 1.0);
90               } else if (intr->intrinsic == nir_intrinsic_store_deref) {
91                  alpha = nir_channel(&b, nir_ssa_for_src(&b, intr->src[1], 4),
92                                      3);
93               } else {
94                  alpha = nir_channel(&b, nir_ssa_for_src(&b, intr->src[0], 4),
95                                      3);
96               }
97
98               nir_variable *var = nir_variable_create(shader,
99                                                       nir_var_uniform,
100                                                       glsl_float_type(),
101                                                       "gl_AlphaRefMESA");
102               var->num_state_slots = 1;
103               var->state_slots = ralloc_array(var, nir_state_slot, 1);
104               memcpy(var->state_slots[0].tokens,
105                      alpha_ref_state_tokens,
106                      sizeof(var->state_slots[0].tokens));
107               nir_ssa_def *alpha_ref = nir_load_var(&b, var);
108
109               nir_ssa_def *condition =
110                  nir_compare_func(&b, func, alpha, alpha_ref);
111
112               nir_discard_if(&b, nir_inot(&b, condition));
113               shader->info.fs.uses_discard = true;
114            }
115         }
116      }
117
118      nir_metadata_preserve(impl, nir_metadata_block_index |
119                            nir_metadata_dominance);
120   }
121}
122