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.
43  */
44 
45 static void
46 add_half_to_fragcoord(nir_builder *b, nir_intrinsic_instr *intr)
47 {
48    nir_ssa_def *wpos = &intr->dest.ssa;
49 
50    assert(intr->dest.is_ssa);
51 
52    b->cursor = nir_after_instr(&intr->instr);
53 
54    wpos = nir_fadd(b, wpos, nir_imm_vec4(b, 0.5f, 0.5f, 0.0f, 0.0f));
55 
56    nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(wpos),
57                                   wpos->parent_instr);
58 }
59 
60 static bool
61 lower_wpos_center_block(nir_builder *b, nir_block *block)
62 {
63    bool progress = false;
64 
65    nir_foreach_instr(instr, block) {
66       if (instr->type == nir_instr_type_intrinsic) {
67          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
68          if (intr->intrinsic == nir_intrinsic_load_var) {
69             nir_deref_var *dvar = intr->variables[0];
70             nir_variable *var = dvar->var;
71 
72             if (var->data.mode == nir_var_shader_in &&
73                 var->data.location == VARYING_SLOT_POS) {
74                /* gl_FragCoord should not have array/struct deref's: */
75                assert(dvar->deref.child == NULL);
76                add_half_to_fragcoord(b, intr);
77                progress = true;
78             }
79          }
80       }
81    }
82 
83    return progress;
84 }
85 
86 bool
87 nir_lower_wpos_center(nir_shader *shader)
88 {
89    bool progress = false;
90    nir_builder b;
91 
92    assert(shader->stage == MESA_SHADER_FRAGMENT);
93 
94    nir_foreach_function(function, shader) {
95       if (function->impl) {
96          nir_builder_init(&b, function->impl);
97 
98          nir_foreach_block(block, function->impl) {
99             progress = lower_wpos_center_block(&b, block) || progress;
100          }
101          nir_metadata_preserve(function->impl, nir_metadata_block_index |
102                                                nir_metadata_dominance);
103       }
104    }
105 
106    return progress;
107 }
108