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  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
  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
  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
  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
  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
  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.