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annotate src/video/SDL_gamma.c @ 3363:90aec03bf9fd

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Fixed bug #627 Increased accuracy of alpha blend calculation
author Sam Lantinga <slouken@libsdl.org>
date Sat, 10 Oct 2009 07:48:57 +0000
parents 62d4992e5a92
children 4b594623401b
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2009 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 #include "SDL_sysvideo.h"
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27
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28
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29 static void
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30 CalculateGammaRamp(float gamma, Uint16 * ramp)
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31 {
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32 int i;
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33
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34 /* 0.0 gamma is all black */
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35 if (gamma <= 0.0f) {
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36 for (i = 0; i < 256; ++i) {
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37 ramp[i] = 0;
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38 }
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39 return;
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40 } else
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41 /* 1.0 gamma is identity */
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42 if (gamma == 1.0f) {
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43 for (i = 0; i < 256; ++i) {
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44 ramp[i] = (i << 8) | i;
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45 }
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46 return;
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47 } else
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48 /* Calculate a real gamma ramp */
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49 {
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50 int value;
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51 gamma = 1.0f / gamma;
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52 for (i = 0; i < 256; ++i) {
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53 value =
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54 (int) (SDL_pow((double) i / 256.0, gamma) * 65535.0 + 0.5);
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55 if (value > 65535) {
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56 value = 65535;
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57 }
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58 ramp[i] = (Uint16) value;
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59 }
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60 }
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61 }
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62
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63 static void
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64 CalculateGammaFromRamp(float *gamma, Uint16 * ramp)
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65 {
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66 /* The following is adapted from a post by Garrett Bass on OpenGL
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67 Gamedev list, March 4, 2000.
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68 */
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69 float sum = 0.0f;
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70 int i, count = 0;
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71
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72 *gamma = 1.0;
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73 for (i = 1; i < 256; ++i) {
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74 if ((ramp[i] != 0) && (ramp[i] != 65535)) {
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75 double B = (double) i / 256.0;
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76 double A = ramp[i] / 65535.0;
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77 sum += (float) (SDL_log(A) / SDL_log(B));
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78 count++;
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79 }
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80 }
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81 if (count && sum > 0.0f) {
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82 *gamma = 1.0f / (sum / count);
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83 }
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84 }
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85
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86 int
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87 SDL_SetGamma(float red, float green, float blue)
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88 {
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89 Uint16 ramp[3][256];
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90
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91 CalculateGammaRamp(red, ramp[0]);
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92 CalculateGammaRamp(green, ramp[1]);
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93 CalculateGammaRamp(blue, ramp[2]);
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94
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95 return SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
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96 }
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97
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98 /* Calculating the gamma by integrating the gamma ramps isn't exact,
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99 so this function isn't officially supported.
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100 */
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101 int
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102 SDL_GetGamma(float *red, float *green, float *blue)
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103 {
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104 int succeeded;
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105 Uint16 ramp[3][256];
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106
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107 succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
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108 if (succeeded >= 0) {
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109 CalculateGammaFromRamp(red, ramp[0]);
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110 CalculateGammaFromRamp(green, ramp[1]);
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111 CalculateGammaFromRamp(blue, ramp[2]);
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112 }
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113 return succeeded;
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114 }
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115
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116 int
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117 SDL_SetGammaRamp(const Uint16 * red, const Uint16 * green,
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118 const Uint16 * blue)
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119 {
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120 SDL_VideoDevice *_this = SDL_GetVideoDevice();
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121 int succeeded;
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122
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123 /* Lazily allocate the gamma tables */
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124 if (!SDL_CurrentDisplay.gamma) {
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125 SDL_GetGammaRamp(NULL, NULL, NULL);
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126 }
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127
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128 /* Fill the gamma table with the new values */
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129 if (red) {
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130 SDL_memcpy(&SDL_CurrentDisplay.gamma[0 * 256], red,
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131 256 * sizeof(*SDL_CurrentDisplay.gamma));
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132 }
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133 if (green) {
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134 SDL_memcpy(&SDL_CurrentDisplay.gamma[1 * 256], green,
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135 256 * sizeof(*SDL_CurrentDisplay.gamma));
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136 }
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137 if (blue) {
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138 SDL_memcpy(&SDL_CurrentDisplay.gamma[2 * 256], blue,
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139 256 * sizeof(*SDL_CurrentDisplay.gamma));
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140 }
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141
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142 /* Try to set the gamma ramp in the driver */
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143 succeeded = -1;
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144 if (_this && _this->SetDisplayGammaRamp) {
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145 if (SDL_GetFocusWindow()) {
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146 succeeded =
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147 _this->SetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
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148 } else {
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149 succeeded = 0;
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150 }
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151 } else {
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152 SDL_SetError("Gamma ramp manipulation not supported");
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153 }
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154 return succeeded;
0
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155 }
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156
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157 int
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158 SDL_GetGammaRamp(Uint16 * red, Uint16 * green, Uint16 * blue)
0
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159 {
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160 SDL_VideoDevice *_this = SDL_GetVideoDevice();
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161
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162 /* Lazily allocate the gamma table */
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163 if (!SDL_CurrentDisplay.gamma) {
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164 size_t rampsize = (3 * 256 * sizeof(*SDL_CurrentDisplay.gamma));
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165
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166 SDL_CurrentDisplay.gamma = SDL_malloc(rampsize * 2);
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167 if (!SDL_CurrentDisplay.gamma) {
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168 SDL_OutOfMemory();
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169 return -1;
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170 }
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171 if (_this && _this->GetDisplayGammaRamp) {
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172 /* Get the real hardware gamma */
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173 _this->GetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
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174 } else {
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175 /* Assume an identity gamma */
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176 int i;
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177 for (i = 0; i < 256; ++i) {
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178 SDL_CurrentDisplay.gamma[0 * 256 + i] = (i << 8) | i;
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179 SDL_CurrentDisplay.gamma[1 * 256 + i] = (i << 8) | i;
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180 SDL_CurrentDisplay.gamma[2 * 256 + i] = (i << 8) | i;
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181 }
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182 }
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183 SDL_CurrentDisplay.saved_gamma = SDL_CurrentDisplay.gamma + (3 * 256);
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184 SDL_memcpy(SDL_CurrentDisplay.saved_gamma, SDL_CurrentDisplay.gamma,
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185 rampsize);
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186 }
0
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187
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188 /* Just copy from our internal table */
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189 if (red) {
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190 SDL_memcpy(red, &SDL_CurrentDisplay.gamma[0 * 256],
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191 256 * sizeof(*red));
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192 }
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193 if (green) {
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194 SDL_memcpy(green, &SDL_CurrentDisplay.gamma[1 * 256],
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195 256 * sizeof(*green));
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196 }
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197 if (blue) {
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198 SDL_memcpy(blue, &SDL_CurrentDisplay.gamma[2 * 256],
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199 256 * sizeof(*blue));
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200 }
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201 return 0;
0
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202 }
1895
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203
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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204 /* vi: set ts=4 sw=4 expandtab: */