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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
update_fragcoord(nir_builder * b,nir_intrinsic_instr * intr,const bool for_sample_shading)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
lower_wpos_center_block(nir_builder * b,nir_block * block,const bool for_sample_shading)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
nir_lower_wpos_center(nir_shader * shader,const bool for_sample_shading)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 }
116