1 /**************************************************************************
2 *
3 * Copyright 2010 VMware, Inc.
4 * All Rights Reserved.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the
8 * "Software"), to deal in the Software without restriction, including
9 * without limitation the rights to use, copy, modify, merge, publish,
10 * distribute, sub license, and/or sell copies of the Software, and to
11 * permit persons to whom the Software is furnished to do so, subject to
12 * the following conditions:
13 *
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
17 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
18 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
19 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
20 * USE OR OTHER DEALINGS IN THE SOFTWARE.
21 *
22 * The above copyright notice and this permission notice (including the
23 * next paragraph) shall be included in all copies or substantial portions
24 * of the Software.
25 *
26 **************************************************************************/
27
28 /**
29 * @file
30 * SRGB translation.
31 *
32 * @author Brian Paul <brianp@vmware.com>
33 * @author Michal Krol <michal@vmware.com>
34 * @author Jose Fonseca <jfonseca@vmware.com>
35 */
36
37 #ifndef U_FORMAT_SRGB_H_
38 #define U_FORMAT_SRGB_H_
39
40 #include <stdint.h>
41 #include <math.h>
42 #include "c99_compat.h"
43
44 extern const float
45 util_format_srgb_8unorm_to_linear_float_table[256];
46
47 extern const uint8_t
48 util_format_srgb_to_linear_8unorm_table[256];
49
50 extern const uint8_t
51 util_format_linear_to_srgb_8unorm_table[256];
52
53 extern const unsigned
54 util_format_linear_to_srgb_helper_table[104];
55
56
57 static inline float
util_format_linear_to_srgb_float(float cl)58 util_format_linear_to_srgb_float(float cl)
59 {
60 if (cl <= 0.0f)
61 return 0.0f;
62 else if (cl < 0.0031308f)
63 return 12.92f * cl;
64 else if (cl < 1.0f)
65 return 1.055f * powf(cl, 0.41666f) - 0.055f;
66 else
67 return 1.0f;
68 }
69
70
71 /**
72 * Convert a unclamped linear float to srgb value in the [0,255].
73 */
74 static inline uint8_t
util_format_linear_float_to_srgb_8unorm(float x)75 util_format_linear_float_to_srgb_8unorm(float x)
76 {
77 /*
78 * This is taken from https://gist.github.com/rygorous/2203834
79 * Use LUT and do linear interpolation.
80 */
81 union {
82 uint32_t ui;
83 float f;
84 } almostone, minval, f;
85 unsigned tab, bias, scale, t;
86
87 almostone.ui = 0x3f7fffff;
88 minval.ui = (127-13) << 23;
89
90 /*
91 * Clamp to [2^(-13), 1-eps]; these two values map to 0 and 1, respectively.
92 * The tests are carefully written so that NaNs map to 0, same as in the
93 * reference implementation.
94 */
95 if (!(x > minval.f))
96 x = minval.f;
97 if (x > almostone.f)
98 x = almostone.f;
99
100 /* Do the table lookup and unpack bias, scale */
101 f.f = x;
102 tab = util_format_linear_to_srgb_helper_table[(f.ui - minval.ui) >> 20];
103 bias = (tab >> 16) << 9;
104 scale = tab & 0xffff;
105
106 /* Grab next-highest mantissa bits and perform linear interpolation */
107 t = (f.ui >> 12) & 0xff;
108 return (uint8_t) ((bias + scale*t) >> 16);
109 }
110
111
112 /**
113 * Convert an 8-bit sRGB value from non-linear space to a
114 * linear RGB value in [0, 1].
115 * Implemented with a 256-entry lookup table.
116 */
117 static inline float
util_format_srgb_8unorm_to_linear_float(uint8_t x)118 util_format_srgb_8unorm_to_linear_float(uint8_t x)
119 {
120 return util_format_srgb_8unorm_to_linear_float_table[x];
121 }
122
123
124 /*
125 * XXX These 2 functions probably don't make a lot of sense (but lots
126 * of potential callers which most likely all don't make sense neither)
127 */
128
129 /**
130 * Convert a 8bit normalized value from linear to srgb.
131 */
132 static inline uint8_t
util_format_linear_to_srgb_8unorm(uint8_t x)133 util_format_linear_to_srgb_8unorm(uint8_t x)
134 {
135 return util_format_linear_to_srgb_8unorm_table[x];
136 }
137
138
139 /**
140 * Convert a 8bit normalized value from srgb to linear.
141 */
142 static inline uint8_t
util_format_srgb_to_linear_8unorm(uint8_t x)143 util_format_srgb_to_linear_8unorm(uint8_t x)
144 {
145 return util_format_srgb_to_linear_8unorm_table[x];
146 }
147
148
149 #endif /* U_FORMAT_SRGB_H_ */
150