1 /*
2 * Copyright (C) 2019 Alyssa Rosenzweig
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
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 */
23
24 /* On some hardware (particularly, all current versions of Mali GPUs),
25 * vertex shaders do not output gl_Position in world-space. Instead, they
26 * output gl_Position in transformed screen space via the "pseudo"
27 * position varying. Thus, this pass finds writes to gl_Position and
28 * changes them to transformed writes, still to gl_Position. The
29 * outputted screen space is still written back to VARYING_SLOT_POS,
30 * which is semantically ambiguous but nevertheless a good match for
31 * Gallium/NIR/Mali.
32 *
33 * Implements coordinate transformation as defined in section 12.5
34 * "Coordinate Transformation" of the OpenGL ES 3.2 full specification.
35 *
36 * This pass must run before lower_vars/lower_io such that derefs are
37 * still in place.
38 */
39
40 #include "nir/nir.h"
41 #include "nir/nir_builder.h"
42
43 static bool
lower_viewport_transform_instr(nir_builder * b,nir_intrinsic_instr * intr,void * data)44 lower_viewport_transform_instr(nir_builder *b, nir_intrinsic_instr *intr,
45 void *data)
46 {
47 if (intr->intrinsic != nir_intrinsic_store_deref)
48 return false;
49
50 nir_variable *var = nir_intrinsic_get_var(intr, 0);
51 if (var->data.mode != nir_var_shader_out ||
52 var->data.location != VARYING_SLOT_POS)
53 return false;
54
55 b->cursor = nir_before_instr(&intr->instr);
56
57 /* Grab the source and viewport */
58 nir_def *input_point = intr->src[1].ssa;
59 nir_def *scale = nir_load_viewport_scale(b);
60 nir_def *offset = nir_load_viewport_offset(b);
61
62 /* World space to normalised device coordinates to screen space */
63
64 nir_def *w_recip = nir_frcp(b, nir_channel(b, input_point, 3));
65
66 nir_def *ndc_point = nir_fmul(b, nir_trim_vector(b, input_point, 3),
67 w_recip);
68
69 nir_def *screen = nir_fadd(b, nir_fmul(b, ndc_point, scale),
70 offset);
71
72 /* gl_Position will be written out in screenspace xyz, with w set to
73 * the reciprocal we computed earlier. The transformed w component is
74 * then used for perspective-correct varying interpolation. The
75 * transformed w component must preserve its original sign; this is
76 * used in depth clipping computations
77 */
78
79 nir_def *screen_space = nir_vec4(b,
80 nir_channel(b, screen, 0),
81 nir_channel(b, screen, 1),
82 nir_channel(b, screen, 2),
83 w_recip);
84
85 nir_src_rewrite(&intr->src[1], screen_space);
86 return true;
87 }
88
89 bool
nir_lower_viewport_transform(nir_shader * shader)90 nir_lower_viewport_transform(nir_shader *shader)
91 {
92 assert((shader->info.stage == MESA_SHADER_VERTEX) || (shader->info.stage == MESA_SHADER_GEOMETRY) || (shader->info.stage == MESA_SHADER_TESS_EVAL));
93
94 return nir_shader_intrinsics_pass(shader, lower_viewport_transform_instr,
95 nir_metadata_control_flow,
96 NULL);
97 }
98