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
47static void
48update_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, wpos,
71                                  wpos->parent_instr);
72}
73
74static bool
75lower_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
93bool
94nir_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}
116