src/compiler/nir/nir_lower_alpha_test.c

   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
  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_deref:
  59                   out = nir_deref_instr_get_variable(nir_src_as_deref(intr->src[0]));
  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 if (intr->intrinsic == nir_intrinsic_store_deref) {
  89                   alpha = nir_channel(&b, nir_ssa_for_src(&b, intr->src[1], 4),
  90                                       3);
  91                } else {
  92                   alpha = nir_channel(&b, nir_ssa_for_src(&b, intr->src[0], 4),
  93                                       3);
  94                }
  95
  96                nir_ssa_def *condition =
  97                   nir_compare_func(&b, func,
  98                                    alpha, nir_load_alpha_ref_float(&b));
  99
 100                nir_intrinsic_instr *discard =
 101                   nir_intrinsic_instr_create(b.shader,
 102                                              nir_intrinsic_discard_if);
 103                discard->num_components = 1;
 104                discard->src[0] = nir_src_for_ssa(nir_inot(&b, condition));
 105                nir_builder_instr_insert(&b, &discard->instr);
 106                shader->info.fs.uses_discard = true;
 107             }
 108          }
 109       }
 110
 111       nir_metadata_preserve(impl, nir_metadata_block_index |
 112                             nir_metadata_dominance);
 113    }
 114 }