src/util/format_srgb.py

   1 from __future__ import print_function
   2
   3 CopyRight = '''
   4 /**************************************************************************
   5  *
   6  * Copyright 2010 VMware, Inc.
   7  * All Rights Reserved.
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a
  10  * copy of this software and associated documentation files (the
  11  * "Software"), to deal in the Software without restriction, including
  12  * without limitation the rights to use, copy, modify, merge, publish,
  13  * distribute, sub license, and/or sell copies of the Software, and to
  14  * permit persons to whom the Software is furnished to do so, subject to
  15  * the following conditions:
  16  *
  17  * The above copyright notice and this permission notice (including the
  18  * next paragraph) shall be included in all copies or substantial portions
  19  * of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  22  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  24  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
  25  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  26  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  27  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28  *
  29  **************************************************************************/
  30
  31 /**
  32  * @file
  33  * SRGB translation.
  34  *
  35  * @author Brian Paul <brianp@vmware.com>
  36  * @author Michal Krol <michal@vmware.com>
  37  * @author Jose Fonseca <jfonseca@vmware.com>
  38  */
  39 '''
  40
  41
  42 import math
  43 import struct
  44
  45
  46 def srgb_to_linear(x):
  47     if x <= 0.04045:
  48         return x / 12.92
  49     else:
  50         return math.pow((x + 0.055) / 1.055, 2.4)
  51
  52
  53 def linear_to_srgb(x):
  54     if x >= 0.0031308:
  55         return 1.055 * math.pow(x, 0.41666666) - 0.055
  56     else:
  57         return 12.92 * x
  58
  59
  60 def generate_srgb_tables():
  61     print('const float')
  62     print('util_format_srgb_8unorm_to_linear_float_table[256] = {')
  63     for j in range(0, 256, 4):
  64         print('   ', end=' ')
  65         print(' '.join(['%.7ef,' % srgb_to_linear(i / 255.0) for i in range(j, j + 4)]))
  66     print('};')
  67     print()
  68     print('const uint8_t')
  69     print('util_format_srgb_to_linear_8unorm_table[256] = {')
  70     for j in range(0, 256, 16):
  71         print('   ', end=' ')
  72         print(' '.join(['%3u,' % int(srgb_to_linear(i / 255.0) * 255.0 + 0.5) for i in range(j, j + 16)]))
  73     print('};')
  74     print()
  75     print('const uint8_t')
  76     print('util_format_linear_to_srgb_8unorm_table[256] = {')
  77     for j in range(0, 256, 16):
  78         print('   ', end=' ')
  79         print(' '.join(['%3u,' % int(linear_to_srgb(i / 255.0) * 255.0 + 0.5) for i in range(j, j + 16)]))
  80     print('};')
  81     print()
  82
  83 # calculate the table interpolation values used in float linear to unorm8 srgb
  84     numexp = 13
  85     mantissa_msb = 3
  86 # stepshift is just used to only use every x-th float to make things faster,
  87 # 5 is largest value which still gives exact same table as 0
  88     stepshift = 5
  89     nbuckets = numexp << mantissa_msb
  90     bucketsize = (1 << (23 - mantissa_msb)) >> stepshift
  91     mantshift = 12
  92     valtable = []
  93     sum_aa = float(bucketsize)
  94     sum_ab = 0.0
  95     sum_bb = 0.0
  96     for i in range(0, bucketsize):
  97         j = (i << stepshift) >> mantshift
  98         sum_ab += j
  99         sum_bb += j*j
 100     inv_det = 1.0 / (sum_aa * sum_bb - sum_ab * sum_ab)
 101
 102     for bucket in range(0, nbuckets):
 103         start = ((127 - numexp) << 23) + bucket*(bucketsize << stepshift)
 104         sum_a = 0.0
 105         sum_b = 0.0
 106
 107         for i in range(0, bucketsize):
 108             j = (i << stepshift) >> mantshift
 109             fint = start + (i << stepshift)
 110             ffloat = struct.unpack('f', struct.pack('I', fint))[0]
 111             val = linear_to_srgb(ffloat) * 255.0 + 0.5
 112             sum_a += val
 113             sum_b += j*val
 114
 115         solved_a = inv_det * (sum_bb*sum_a - sum_ab*sum_b)
 116         solved_b = inv_det * (sum_aa*sum_b - sum_ab*sum_a)
 117
 118         scaled_a = solved_a * 65536.0 / 512.0
 119         scaled_b = solved_b * 65536.0
 120
 121         int_a = int(scaled_a + 0.5)
 122         int_b = int(scaled_b + 0.5)
 123
 124         valtable.append((int_a << 16) + int_b)
 125
 126     print('const unsigned')
 127     print('util_format_linear_to_srgb_helper_table[104] = {')
 128
 129     for j in range(0, nbuckets, 4):
 130         print('   ', end=' ')
 131         print(' '.join(['0x%08x,' % valtable[i] for i in range(j, j + 4)]))
 132     print('};')
 133     print()
 134
 135 def main():
 136     print('/* This file is autogenerated by u_format_srgb.py. Do not edit directly. */')
 137     print()
 138     # This will print the copyright message on the top of this file
 139     print(CopyRight.strip())
 140     print()
 141     print('#include "format_srgb.h"')
 142     print()
 143     generate_srgb_tables()
 144
 145
 146 if __name__ == '__main__':
 147     main()