annotate src/video/SDL_gamma.c @ 2278:85cbe9c892f4

Merged revision 3455 from SDL 1.2, fixing documentation typo.
author Sam Lantinga <slouken@libsdl.org>
date Fri, 28 Dec 2007 07:54:35 +0000
parents c121d94672cb
children e1da92da346c
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2006 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22 #include "SDL_config.h"
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23
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24 /* Gamma correction support */
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25
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26 #ifdef HAVE_MATH_H
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27 #include <math.h> /* Used for calculating gamma ramps */
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28 #else
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29 /* Math routines from uClibc: http://www.uclibc.org */
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30 #include "math_private.h"
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31 #include "e_sqrt.h"
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32 #include "e_pow.h"
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33 #include "e_log.h"
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34 #define pow(x, y) __ieee754_pow(x, y)
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35 #define log(x) __ieee754_log(x)
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36 #endif
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37
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38 #include "SDL_sysvideo.h"
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39
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40
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41 static void
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42 CalculateGammaRamp(float gamma, Uint16 * ramp)
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43 {
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44 int i;
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45
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46 /* 0.0 gamma is all black */
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47 if (gamma <= 0.0f) {
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48 for (i = 0; i < 256; ++i) {
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49 ramp[i] = 0;
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50 }
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51 return;
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52 } else
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53 /* 1.0 gamma is identity */
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54 if (gamma == 1.0f) {
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55 for (i = 0; i < 256; ++i) {
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56 ramp[i] = (i << 8) | i;
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57 }
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58 return;
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59 } else
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60 /* Calculate a real gamma ramp */
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61 {
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62 int value;
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63 gamma = 1.0f / gamma;
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64 for (i = 0; i < 256; ++i) {
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65 value = (int) (pow((double) i / 256.0, gamma) * 65535.0 + 0.5);
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66 if (value > 65535) {
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67 value = 65535;
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68 }
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69 ramp[i] = (Uint16) value;
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70 }
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71 }
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72 }
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73 static void
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74 CalculateGammaFromRamp(float *gamma, Uint16 * ramp)
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75 {
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76 /* The following is adapted from a post by Garrett Bass on OpenGL
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77 Gamedev list, March 4, 2000.
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78 */
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79 float sum = 0.0f;
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80 int i, count = 0;
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81
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82 *gamma = 1.0;
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83 for (i = 1; i < 256; ++i) {
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84 if ((ramp[i] != 0) && (ramp[i] != 65535)) {
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85 double B = (double) i / 256.0;
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86 double A = ramp[i] / 65535.0;
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87 sum += (float) (log(A) / log(B));
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88 count++;
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89 }
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90 }
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91 if (count && sum > 0.0f) {
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92 *gamma = 1.0f / (sum / count);
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93 }
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94 }
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95
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96 int
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97 SDL_SetGamma(float red, float green, float blue)
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98 {
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99 Uint16 ramp[3][256];
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100
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101 CalculateGammaRamp(red, ramp[0]);
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102 CalculateGammaRamp(green, ramp[1]);
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103 CalculateGammaRamp(blue, ramp[2]);
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104
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105 return SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
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106 }
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107
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108 /* Calculating the gamma by integrating the gamma ramps isn't exact,
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109 so this function isn't officially supported.
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110 */
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111 int
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112 SDL_GetGamma(float *red, float *green, float *blue)
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113 {
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114 int succeeded;
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115 Uint16 ramp[3][256];
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116
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117 succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
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118 if (succeeded >= 0) {
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119 CalculateGammaFromRamp(red, ramp[0]);
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120 CalculateGammaFromRamp(green, ramp[1]);
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121 CalculateGammaFromRamp(blue, ramp[2]);
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122 }
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123 return succeeded;
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124 }
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125
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126 int
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127 SDL_SetGammaRamp(const Uint16 * red, const Uint16 * green,
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128 const Uint16 * blue)
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129 {
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130 SDL_VideoDevice *_this = SDL_GetVideoDevice();
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131 int succeeded;
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132
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133 /* Lazily allocate the gamma tables */
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134 if (!SDL_CurrentDisplay.gamma) {
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135 SDL_GetGammaRamp(NULL, NULL, NULL);
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136 }
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137
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138 /* Fill the gamma table with the new values */
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139 if (red) {
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140 SDL_memcpy(&SDL_CurrentDisplay.gamma[0 * 256], red,
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141 256 * sizeof(*SDL_CurrentDisplay.gamma));
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142 }
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143 if (green) {
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144 SDL_memcpy(&SDL_CurrentDisplay.gamma[1 * 256], green,
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145 256 * sizeof(*SDL_CurrentDisplay.gamma));
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146 }
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147 if (blue) {
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148 SDL_memcpy(&SDL_CurrentDisplay.gamma[2 * 256], blue,
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149 256 * sizeof(*SDL_CurrentDisplay.gamma));
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150 }
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151
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152 /* Try to set the gamma ramp in the driver */
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153 succeeded = -1;
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154 if (_this && _this->SetDisplayGammaRamp) {
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155 if (SDL_GetFocusWindow()) {
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156 succeeded =
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157 _this->SetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
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158 } else {
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159 succeeded = 0;
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160 }
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161 } else {
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162 SDL_SetError("Gamma ramp manipulation not supported");
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163 }
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164 return succeeded;
0
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165 }
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166
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167 int
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168 SDL_GetGammaRamp(Uint16 * red, Uint16 * green, Uint16 * blue)
0
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169 {
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170 SDL_VideoDevice *_this = SDL_GetVideoDevice();
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171
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172 /* Lazily allocate the gamma table */
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173 if (!SDL_CurrentDisplay.gamma) {
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174 size_t rampsize = (3 * 256 * sizeof(*SDL_CurrentDisplay.gamma));
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175
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176 SDL_CurrentDisplay.gamma = SDL_malloc(rampsize * 2);
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177 if (!SDL_CurrentDisplay.gamma) {
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178 SDL_OutOfMemory();
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179 return -1;
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180 }
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181 if (_this && _this->GetDisplayGammaRamp) {
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182 /* Get the real hardware gamma */
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183 _this->GetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
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184 } else {
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185 /* Assume an identity gamma */
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186 int i;
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187 for (i = 0; i < 256; ++i) {
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188 SDL_CurrentDisplay.gamma[0 * 256 + i] = (i << 8) | i;
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189 SDL_CurrentDisplay.gamma[1 * 256 + i] = (i << 8) | i;
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190 SDL_CurrentDisplay.gamma[2 * 256 + i] = (i << 8) | i;
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191 }
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192 }
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193 SDL_CurrentDisplay.saved_gamma = SDL_CurrentDisplay.gamma + (3 * 256);
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194 SDL_memcpy(SDL_CurrentDisplay.saved_gamma, SDL_CurrentDisplay.gamma,
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195 rampsize);
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196 }
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197
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198 /* Just copy from our internal table */
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199 if (red) {
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200 SDL_memcpy(red, &SDL_CurrentDisplay.gamma[0 * 256],
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201 256 * sizeof(*red));
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202 }
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203 if (green) {
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204 SDL_memcpy(green, &SDL_CurrentDisplay.gamma[1 * 256],
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205 256 * sizeof(*green));
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diff changeset
206 }
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diff changeset
207 if (blue) {
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diff changeset
208 SDL_memcpy(blue, &SDL_CurrentDisplay.gamma[2 * 256],
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diff changeset
209 256 * sizeof(*blue));
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diff changeset
210 }
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diff changeset
211 return 0;
0
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212 }
1895
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213
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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214 /* vi: set ts=4 sw=4 expandtab: */