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      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_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