src/compiler/nir/nir_lower_fb_read.c

   1 /*
   2  * Copyright © 2019 Google, Inc.
   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 FROM,
  20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  21  * SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25 #include "nir_builder.h"
  26
  27 /* Lowing for fragment shader load_output.
  28  *
  29  * This pass supports the blend_equation_advanced, where a fragment
  30  * shader loads the output (fragcolor) to read the current framebuffer.
  31  * It does this by lowering the output read to a txf_ms_fb instruction.
  32  * This instruction works similarly to a normal txf_ms except without
  33  * taking a texture source argument.  (The driver backend is expected
  34  * to wire this up to a free texture slot which is configured to read
  35  * from the framebuffer.)
  36  *
  37  * This should be run after lower_wpos_ytransform, because the tex
  38  * coordinates should be the physical fragcoord, not the logical
  39  * y-flipped coord.
  40  *
  41  * Note that this pass explicitly does *not* add a sampler uniform
  42  * (as txf_ms_fb does not reference a texture).  The driver backend
  43  * is going to want nif->info.num_textures to include the count of
  44  * number of textures *not* including the one it inserts to sample
  45  * from the framebuffer, so it more easily knows where to insert the
  46  * hidden texture to read from the fb.
  47  */
  48
  49 static void
  50 lower_fb_read(nir_builder *b, nir_intrinsic_instr *intr)
  51 {
  52    b->cursor = nir_before_instr(&intr->instr);
  53
  54    nir_ssa_def *fragcoord = nir_load_frag_coord(b);
  55    nir_ssa_def *sampid = nir_load_sample_id(b);
  56
  57    fragcoord = nir_f2i32(b, fragcoord);
  58
  59    nir_tex_instr *tex = nir_tex_instr_create(b->shader, 2);
  60    tex->op = nir_texop_txf_ms_fb;
  61    tex->sampler_dim = GLSL_SAMPLER_DIM_2D;
  62    tex->coord_components = 2;
  63    tex->dest_type = nir_type_float;
  64    tex->src[0].src_type = nir_tex_src_coord;
  65    tex->src[0].src = nir_src_for_ssa(nir_channels(b, fragcoord, 0x3));
  66    tex->src[1].src_type = nir_tex_src_ms_index;
  67    tex->src[1].src = nir_src_for_ssa(sampid);
  68
  69    nir_ssa_dest_init(&tex->instr, &tex->dest, 4, 32, NULL);
  70    nir_builder_instr_insert(b, &tex->instr);
  71
  72    nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(&tex->dest.ssa));
  73 }
  74
  75 bool
  76 nir_lower_fb_read(nir_shader *shader)
  77 {
  78    bool progress = false;
  79
  80    assert(shader->info.stage == MESA_SHADER_FRAGMENT);
  81
  82    nir_foreach_function(function, shader) {
  83       nir_function_impl *impl = function->impl;
  84
  85       if (!impl)
  86          continue;
  87
  88       nir_foreach_block(block, impl) {
  89          nir_foreach_instr_safe(instr, block) {
  90             if (instr->type != nir_instr_type_intrinsic)
  91                continue;
  92
  93             nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
  94             if (intr->intrinsic != nir_intrinsic_load_output)
  95                continue;
  96
  97             /* TODO KHR_blend_equation_advanced is limited to non-MRT
  98              * scenarios.. but possible there are other extensions
  99              * where this pass would be useful that do support MRT?
 100              *
 101              * I guess for now I'll leave that as an exercise for the
 102              * reader.
 103              */
 104             if (nir_intrinsic_base(intr) != 0 ||
 105                 nir_src_as_uint(intr->src[0]) != 0)
 106                continue;
 107
 108             nir_builder b;
 109             nir_builder_init(&b, impl);
 110             lower_fb_read(&b, intr);
 111             progress = true;
 112          }
 113       }
 114
 115       nir_metadata_preserve(impl, nir_metadata_block_index |
 116                                   nir_metadata_dominance);
 117
 118    }
 119
 120    return progress;
 121 }