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,
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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
44extern const float
45util_format_srgb_8unorm_to_linear_float_table[256];
46
47extern const uint8_t
48util_format_srgb_to_linear_8unorm_table[256];
49
50extern const uint8_t
51util_format_linear_to_srgb_8unorm_table[256];
52
53extern const unsigned
54util_format_linear_to_srgb_helper_table[104];
55
56
57static inline float
58util_format_srgb_to_linear_float(float cs)
59{
60   if (cs <= 0.0f)
61      return 0.0f;
62   else if (cs <= 0.04045f)
63      return cs / 12.92f;
64   else if (cs < 1.0f)
65      return powf((cs + 0.055) / 1.055f, 2.4f);
66   else
67      return 1.0f;
68}
69
70
71static inline float
72util_format_linear_to_srgb_float(float cl)
73{
74   if (cl <= 0.0f)
75      return 0.0f;
76   else if (cl < 0.0031308f)
77      return 12.92f * cl;
78   else if (cl < 1.0f)
79      return 1.055f * powf(cl, 0.41666f) - 0.055f;
80   else
81      return 1.0f;
82}
83
84
85/**
86 * Convert a unclamped linear float to srgb value in the [0,255].
87 */
88static inline uint8_t
89util_format_linear_float_to_srgb_8unorm(float x)
90{
91   /*
92    * This is taken from https://gist.github.com/rygorous/2203834
93    * Use LUT and do linear interpolation.
94    */
95   union {
96      uint32_t ui;
97      float f;
98   } almostone, minval, f;
99   unsigned tab, bias, scale, t;
100
101   almostone.ui = 0x3f7fffff;
102   minval.ui = (127-13) << 23;
103
104   /*
105    * Clamp to [2^(-13), 1-eps]; these two values map to 0 and 1, respectively.
106    * The tests are carefully written so that NaNs map to 0, same as in the
107    * reference implementation.
108    */
109   if (!(x > minval.f))
110      x = minval.f;
111   if (x > almostone.f)
112      x = almostone.f;
113
114   /* Do the table lookup and unpack bias, scale */
115   f.f = x;
116   tab = util_format_linear_to_srgb_helper_table[(f.ui - minval.ui) >> 20];
117   bias = (tab >> 16) << 9;
118   scale = tab & 0xffff;
119
120   /* Grab next-highest mantissa bits and perform linear interpolation */
121   t = (f.ui >> 12) & 0xff;
122   return (uint8_t) ((bias + scale*t) >> 16);
123}
124
125
126/**
127 * Convert an 8-bit sRGB value from non-linear space to a
128 * linear RGB value in [0, 1].
129 * Implemented with a 256-entry lookup table.
130 */
131static inline float
132util_format_srgb_8unorm_to_linear_float(uint8_t x)
133{
134   return util_format_srgb_8unorm_to_linear_float_table[x];
135}
136
137
138/*
139 * XXX These 2 functions probably don't make a lot of sense (but lots
140 * of potential callers which most likely all don't make sense neither)
141 */
142
143/**
144 * Convert a 8bit normalized value from linear to srgb.
145 */
146static inline uint8_t
147util_format_linear_to_srgb_8unorm(uint8_t x)
148{
149   return util_format_linear_to_srgb_8unorm_table[x];
150}
151
152
153/**
154 * Convert a 8bit normalized value from srgb to linear.
155 */
156static inline uint8_t
157util_format_srgb_to_linear_8unorm(uint8_t x)
158{
159   return util_format_srgb_to_linear_8unorm_table[x];
160}
161
162
163#endif /* U_FORMAT_SRGB_H_ */
164