src/compiler/nir/nir_lower_wpos_center.c

   1 /*
   2  * Copyright © 2015 Red Hat
   3  * Copyright © 2016 Intel Corporation
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  */
  24
  25 #include "nir.h"
  26 #include "nir_builder.h"
  27 #include "program/prog_instruction.h"
  28
  29 /**
  30  * This pass adds <0.5, 0.5> to all uses of gl_FragCoord.
  31  *
  32  * Run before nir_lower_io().
  33  *
  34  * For a more full featured pass, consider using nir_lower_wpos_ytransform(),
  35  * which can handle pixel center integer / half integer, and origin lower
  36  * left / upper left transformations.
  37  *
  38  * This simple pass is primarily intended for use by Vulkan drivers on
  39  * hardware which provides an integer pixel center.  Vulkan mandates that
  40  * the pixel center must be half-integer, and also that the coordinate
  41  * system's origin must be upper left.  This means that there's no need
  42  * for a uniform - we can always just add a constant. In the case that
  43  * sample shading is enabled, Vulkan expects FragCoord to include sample
  44  * positions.
  45  */
  46
  47 static void
  48 update_fragcoord(nir_builder *b, nir_intrinsic_instr *intr,
  49                  const bool for_sample_shading)
  50 {
  51    nir_ssa_def *wpos = &intr->dest.ssa;
  52
  53    assert(intr->dest.is_ssa);
  54
  55    b->cursor = nir_after_instr(&intr->instr);
  56
  57    if (!for_sample_shading) {
  58       wpos = nir_fadd(b, wpos, nir_imm_vec4(b, 0.5f, 0.5f, 0.0f, 0.0f));
  59    } else {
  60       nir_ssa_def *spos = nir_load_sample_pos(b);
  61
  62       wpos = nir_fadd(b, wpos,
  63                       nir_vec4(b,
  64                                nir_channel(b, spos, 0),
  65                                nir_channel(b, spos, 1),
  66                                nir_imm_float(b, 0.0f),
  67                                nir_imm_float(b, 0.0f)));
  68    }
  69
  70    nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(wpos),
  71                                   wpos->parent_instr);
  72 }
  73
  74 static bool
  75 lower_wpos_center_block(nir_builder *b, nir_block *block,
  76                         const bool for_sample_shading)
  77 {
  78    bool progress = false;
  79
  80    nir_foreach_instr(instr, block) {
  81       if (instr->type == nir_instr_type_intrinsic) {
  82          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
  83          if (intr->intrinsic == nir_intrinsic_load_frag_coord) {
  84             update_fragcoord(b, intr, for_sample_shading);
  85             progress = true;
  86          }
  87       }
  88    }
  89
  90    return progress;
  91 }
  92
  93 bool
  94 nir_lower_wpos_center(nir_shader *shader, const bool for_sample_shading)
  95 {
  96    bool progress = false;
  97    nir_builder b;
  98
  99    assert(shader->info.stage == MESA_SHADER_FRAGMENT);
 100
 101    nir_foreach_function(function, shader) {
 102       if (function->impl) {
 103          nir_builder_init(&b, function->impl);
 104
 105          nir_foreach_block(block, function->impl) {
 106             progress = lower_wpos_center_block(&b, block, for_sample_shading) ||
 107                        progress;
 108          }
 109          nir_metadata_preserve(function->impl, nir_metadata_block_index |
 110                                                nir_metadata_dominance);
 111       }
 112    }
 113
 114    return progress;
 115 }