1 /*
2 * Copyright © 2023 Google LLC
3 * SPDX-License-Identifier: MIT
4 */
5
6 #include "nir_builder.h"
7 #include "nir_builtin_builder.h"
8 #include "st_nir.h"
9
10 static nir_def *
fog_result(nir_builder * b,nir_def * color,enum gl_fog_mode fog_mode,struct gl_program_parameter_list * paramList)11 fog_result(nir_builder *b, nir_def *color, enum gl_fog_mode fog_mode, struct gl_program_parameter_list *paramList)
12 {
13 nir_shader *s = b->shader;
14 nir_def *baryc = nir_load_barycentric_pixel(b, 32,
15 .interp_mode = INTERP_MODE_SMOOTH);
16 nir_def *fogc = nir_load_interpolated_input(b, 1, 32, baryc, nir_imm_int(b, 0),
17 .io_semantics.location = VARYING_SLOT_FOGC);
18
19 static const gl_state_index16 fog_params_tokens[STATE_LENGTH] = {STATE_FOG_PARAMS_OPTIMIZED};
20 static const gl_state_index16 fog_color_tokens[STATE_LENGTH] = {STATE_FOG_COLOR};
21
22 nir_variable *fog_params_var = st_nir_state_variable_create(s, glsl_vec4_type(), fog_params_tokens);
23 fog_params_var->data.driver_location = _mesa_add_state_reference(paramList, fog_params_tokens);
24 nir_def *params = nir_load_var(b, fog_params_var);
25
26 nir_variable *fog_color_var = st_nir_state_variable_create(s, glsl_vec4_type(), fog_color_tokens);
27 fog_color_var->data.driver_location = _mesa_add_state_reference(paramList, fog_color_tokens);
28 nir_def *fog_color = nir_load_var(b, fog_color_var);
29
30 /* compute the 1 component fog factor f */
31 nir_def *f = NULL;
32 switch (fog_mode) {
33 case FOG_LINEAR:
34 /* f = (end - z) / (end - start)
35 *
36 * gl_MesaFogParamsOptimized gives us (-1 / (end - start)) and
37 * (end / (end - start)) so we can generate a single MAD.
38 */
39 f = nir_fmad(b, fogc,
40 nir_channel(b, params, 0),
41 nir_channel(b, params, 1));
42 break;
43 case FOG_EXP:
44 /* f = e^(-(density * fogcoord))
45 *
46 * gl_MesaFogParamsOptimized gives us density/ln(2) so we can
47 * use EXP2 which is generally the native instruction without
48 * having to do any further math on the fog density uniform.
49 */
50 f = nir_fmul(b, fogc, nir_channel(b, params, 2));
51 f = nir_fexp2(b, nir_fneg(b, f));
52 break;
53 case FOG_EXP2:
54 /* f = e^(-(density * fogcoord)^2)
55 *
56 * gl_MesaFogParamsOptimized gives us density/sqrt(ln(2)) so we
57 * can do this like FOG_EXP but with a squaring after the
58 * multiply by density.
59 */
60 f = nir_fmul(b, fogc, nir_channel(b, params, 3));
61 f = nir_fmul(b, f, f);
62 f = nir_fexp2(b, nir_fneg(b, f));
63 break;
64 default:
65 unreachable("unsupported fog mode");
66 }
67 f = nir_fsat(b, f);
68
69 /* Not using flrp because we may end up lowering fog after driver lowering
70 * that meant to remove all lrps.
71 */
72 return nir_fmad(b, color, f, nir_fmul(b, fog_color, nir_fsub_imm(b, 1.0, f)));
73 }
74
75 struct lower_fog_state {
76 enum gl_fog_mode fog_mode;
77 struct gl_program_parameter_list *paramList;
78 };
79
80 static bool
st_nir_lower_fog_instr(nir_builder * b,nir_instr * instr,void * _state)81 st_nir_lower_fog_instr(nir_builder *b, nir_instr *instr, void *_state)
82 {
83 const struct lower_fog_state *state = _state;
84
85 if (instr->type != nir_instr_type_intrinsic)
86 return false;
87 nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
88 if (intr->intrinsic != nir_intrinsic_store_output)
89 return false;
90
91 int loc = nir_intrinsic_io_semantics(intr).location;
92 if (loc != FRAG_RESULT_COLOR && loc != FRAG_RESULT_DATA0)
93 return false;
94
95 b->cursor = nir_before_instr(instr);
96
97 nir_def *color = intr->src[0].ssa;
98 color = nir_resize_vector(b, color, 4);
99
100 nir_def *fog = fog_result(b, color, state->fog_mode, state->paramList);
101
102 /* retain the non-fog-blended alpha value for color */
103 color = nir_vector_insert_imm(b, fog, nir_channel(b, color, 3), 3);
104
105 nir_src_rewrite(&intr->src[0],
106 nir_resize_vector(b, color, intr->num_components));
107
108 return true;
109 }
110
111 bool
st_nir_lower_fog(nir_shader * s,enum gl_fog_mode fog_mode,struct gl_program_parameter_list * paramList)112 st_nir_lower_fog(nir_shader *s, enum gl_fog_mode fog_mode, struct gl_program_parameter_list *paramList)
113 {
114 assert(s->info.io_lowered);
115
116 struct lower_fog_state state = {
117 .fog_mode = fog_mode,
118 .paramList = paramList,
119 };
120 return nir_shader_instructions_pass(s, st_nir_lower_fog_instr,
121 nir_metadata_control_flow,
122 &state);
123 }
124