src/compiler/nir/nir_lower_fragcoord_wtrans.c

   1 /*
   2  * Copyright (C) 2019 Andreas Baierl
   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
  27 /* Lower gl_FragCoord and transform the w component
  28  * according to the following pseudocode:
  29  *
  30  *    gl_FragCoord.xyz = gl_FragCoord_orig.xyz
  31  *    gl_FragCoord.w = 1.0 / gl_FragCoord_orig.w
  32  *
  33  * To trigger the transformation, gl_FragCoord currently has to be treated
  34  * as a system value with PIPE_CAP_TGSI_FS_POSITION_IS_SYSVAL enabled.
  35  */
  36
  37 static void
  38 lower_fragcoord_wtrans(nir_builder *b, nir_intrinsic_instr *intr)
  39 {
  40    assert(intr->dest.is_ssa);
  41
  42    b->cursor = nir_before_instr(&intr->instr);
  43
  44    nir_ssa_def *fragcoord_in = nir_load_frag_coord(b);
  45    nir_ssa_def *w_rcp = nir_frcp(b, nir_channel(b, fragcoord_in, 3));
  46    nir_ssa_def *fragcoord_wtrans = nir_vec4(b,
  47                                             nir_channel(b, fragcoord_in, 0),
  48                                             nir_channel(b, fragcoord_in, 1),
  49                                             nir_channel(b, fragcoord_in, 2),
  50                                             w_rcp);
  51    nir_ssa_def_rewrite_uses(&intr->dest.ssa,
  52                             nir_src_for_ssa(fragcoord_wtrans));
  53 }
  54
  55 void
  56 nir_lower_fragcoord_wtrans(nir_shader *shader)
  57 {
  58    assert(shader->info.stage == MESA_SHADER_FRAGMENT);
  59
  60    nir_foreach_function(func, shader) {
  61       if (!func->impl)
  62          continue;
  63
  64       nir_builder b;
  65       nir_builder_init(&b, func->impl);
  66       nir_foreach_block(block, func->impl) {
  67          nir_foreach_instr_safe(instr, block) {
  68             if (instr->type != nir_instr_type_intrinsic)
  69                continue;
  70
  71             nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
  72             if (intr->intrinsic != nir_intrinsic_load_frag_coord)
  73                continue;
  74
  75             lower_fragcoord_wtrans(&b, intr);
  76          }
  77       }
  78       nir_metadata_preserve(func->impl, nir_metadata_block_index |
  79                             nir_metadata_dominance);
  80    }
  81 }