2 * Copyright (C) 2019 Alyssa Rosenzweig
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:
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
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
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
33 * Implements coordinate transformation as defined in section 12.5
34 * "Coordinate Transformation" of the OpenGL ES 3.2 full specification.
36 * This pass must run before lower_vars/lower_io such that derefs are
41 #include "nir/nir_builder.h"
44 nir_lower_viewport_transform(nir_shader
*shader
)
46 assert(shader
->info
.stage
== MESA_SHADER_VERTEX
);
48 nir_foreach_function(func
, shader
) {
49 nir_foreach_block(block
, func
->impl
) {
50 nir_foreach_instr_safe(instr
, block
) {
51 if (instr
->type
!= nir_instr_type_intrinsic
)
54 nir_intrinsic_instr
*intr
= nir_instr_as_intrinsic(instr
);
55 if (intr
->intrinsic
!= nir_intrinsic_store_deref
)
58 nir_variable
*var
= nir_intrinsic_get_var(intr
, 0);
59 if (var
->data
.mode
!= nir_var_shader_out
||
60 var
->data
.location
!= VARYING_SLOT_POS
)
64 nir_builder_init(&b
, func
->impl
);
65 b
.cursor
= nir_before_instr(instr
);
67 /* Grab the source and viewport */
68 nir_ssa_def
*input_point
= nir_ssa_for_src(&b
, intr
->src
[1], 4);
69 nir_ssa_def
*scale
= nir_load_viewport_scale(&b
);
70 nir_ssa_def
*offset
= nir_load_viewport_offset(&b
);
72 /* World space to normalised device coordinates to screen space */
74 nir_ssa_def
*w_recip
= nir_frcp(&b
, nir_channel(&b
, input_point
, 3));
76 nir_ssa_def
*ndc_point
= nir_fmul(&b
,
77 nir_channels(&b
, input_point
, 0x7), w_recip
);
79 nir_ssa_def
*screen
= nir_fadd(&b
,
80 nir_fmul(&b
, ndc_point
, scale
), offset
);
82 /* gl_Position will be written out in screenspace xyz, with w set to
83 * the reciprocal we computed earlier. The transformed w component is
84 * then used for perspective-correct varying interpolation. The
85 * transformed w component must preserve its original sign; this is
86 * used in depth clipping computations
89 nir_ssa_def
*screen_space
= nir_vec4(&b
,
90 nir_channel(&b
, screen
, 0),
91 nir_channel(&b
, screen
, 1),
92 nir_channel(&b
, screen
, 2),
95 nir_instr_rewrite_src(instr
, &intr
->src
[1],
96 nir_src_for_ssa(screen_space
));
100 nir_metadata_preserve(func
->impl
, nir_metadata_block_index
|
101 nir_metadata_dominance
);