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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997, 1998, 1999, 2000, 2001 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 Library General Public
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7 License as published by the Free Software Foundation; either
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8 version 2 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 Library 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 Library General Public
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16 License along with this library; if not, write to the Free
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17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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18
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19 Sam Lantinga
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20 slouken@devolution.com
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21 */
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22
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23 #ifdef SAVE_RCSID
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24 static char rcsid =
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25 "@(#) $Id$";
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26 #endif
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27
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28 /* Gamma correction support */
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29
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30 #define USE_MATH_H /* Used for calculating gamma ramps */
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31
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32 #ifdef USE_MATH_H
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33 #include <math.h>
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34 #endif
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35 #include <stdlib.h>
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36
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37 #include "SDL_error.h"
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38 #include "SDL_sysvideo.h"
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39
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40 #ifdef USE_MATH_H
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41 static void CalculateGammaRamp(float gamma, Uint16 *ramp)
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42 {
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43 int i;
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44
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45 /* 0.0 gamma is all black */
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46 if ( gamma <= 0.0 ) {
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47 for ( i=0; i<256; ++i ) {
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48 ramp[i] = 0;
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49 }
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50 return;
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51 } else
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52 /* 1.0 gamma is identity */
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53 if ( gamma == 1.0 ) {
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54 for ( i=0; i<256; ++i ) {
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55 ramp[i] = (i << 8) | i;
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56 }
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57 return;
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58 } else
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59 /* Calculate a real gamma ramp */
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60 { int value;
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61 gamma = 1.0f / gamma;
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62 for ( i=0; i<256; ++i ) {
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63 value = (int)(pow((double)i/256.0, gamma)*65535.0+0.5);
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64 if ( value > 65535 ) {
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65 value = 65535;
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66 }
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67 ramp[i] = (Uint16)value;
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68 }
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69 }
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70 }
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71 static void CalculateGammaFromRamp(float *gamma, Uint16 *ramp)
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72 {
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73 /* The following is adapted from a post by Garrett Bass on OpenGL
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74 Gamedev list, March 4, 2000.
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75 */
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76 float sum = 0.0;
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77 int i, count = 0;
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78
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79 *gamma = 1.0;
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80 for ( i = 1; i < 256; ++i ) {
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81 if ( (ramp[i] != 0) && (ramp[i] != 65535) ) {
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82 double B = (double)i / 256.0;
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83 double A = ramp[i] / 65535.0;
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84 sum += (float) ( log(A) / log(B) );
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85 count++;
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86 }
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87 }
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88 if ( count && sum ) {
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89 *gamma = 1.0f / (sum / count);
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90 }
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91 }
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92 #endif /* USE_MATH_H */
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93
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94 int SDL_SetGamma(float red, float green, float blue)
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95 {
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96 int succeeded;
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97 SDL_VideoDevice *video = current_video;
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98 SDL_VideoDevice *this = current_video;
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99
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100 succeeded = -1;
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101 #ifdef USE_MATH_H
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102 /* Prefer using SetGammaRamp(), as it's more flexible */
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103 {
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104 Uint16 ramp[3][256];
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105
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106 CalculateGammaRamp(red, ramp[0]);
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107 CalculateGammaRamp(green, ramp[1]);
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108 CalculateGammaRamp(blue, ramp[2]);
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109 succeeded = SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
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110 }
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111 #else
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112 SDL_SetError("Gamma correction not supported");
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113 #endif
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114 if ( (succeeded < 0) && video->SetGamma ) {
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115 SDL_ClearError();
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116 succeeded = video->SetGamma(this, red, green, blue);
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117 }
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118 return succeeded;
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119 }
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120
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121 /* Calculating the gamma by integrating the gamma ramps isn't exact,
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122 so this function isn't officially supported.
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123 */
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124 int SDL_GetGamma(float *red, float *green, float *blue)
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125 {
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126 int succeeded;
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127 SDL_VideoDevice *video = current_video;
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128 SDL_VideoDevice *this = current_video;
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129
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130 succeeded = -1;
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131 #ifdef USE_MATH_H
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132 /* Prefer using GetGammaRamp(), as it's more flexible */
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133 {
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134 Uint16 ramp[3][256];
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135
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136 succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
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137 if ( succeeded >= 0 ) {
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138 CalculateGammaFromRamp(red, ramp[0]);
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139 CalculateGammaFromRamp(green, ramp[1]);
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140 CalculateGammaFromRamp(blue, ramp[2]);
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141 }
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142 }
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143 #else
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144 SDL_SetError("Gamma correction not supported");
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145 #endif
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146 if ( (succeeded < 0) && video->GetGamma ) {
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147 SDL_ClearError();
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148 succeeded = video->GetGamma(this, red, green, blue);
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149 }
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150 return succeeded;
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151 }
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152
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153 int SDL_SetGammaRamp(Uint16 *red, Uint16 *green, Uint16 *blue)
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154 {
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155 int succeeded;
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156 SDL_VideoDevice *video = current_video;
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157 SDL_VideoDevice *this = current_video;
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158 SDL_Surface *screen = SDL_PublicSurface;
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159
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160 /* Verify the screen parameter */
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161 if ( !screen ) {
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162 SDL_SetError("No video mode has been set");
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163 return -1;
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164 }
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165
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166 /* Lazily allocate the gamma tables */
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167 if ( ! video->gamma ) {
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168 SDL_GetGammaRamp(0, 0, 0);
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169 }
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170
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171 /* Fill the gamma table with the new values */
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172 if ( red ) {
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173 memcpy(&video->gamma[0*256], red, 256*sizeof(*video->gamma));
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174 }
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175 if ( green ) {
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176 memcpy(&video->gamma[1*256], green, 256*sizeof(*video->gamma));
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177 }
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178 if ( blue ) {
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179 memcpy(&video->gamma[2*256], blue, 256*sizeof(*video->gamma));
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180 }
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181
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182 /* Gamma correction always possible on split palettes */
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183 if ( (screen->flags & SDL_HWPALETTE) == SDL_HWPALETTE ) {
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184 SDL_Palette *pal = screen->format->palette;
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185
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186 /* If physical palette has been set independently, use it */
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187 if(video->physpal)
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188 pal = video->physpal;
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189
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190 SDL_SetPalette(screen, SDL_PHYSPAL,
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191 pal->colors, 0, pal->ncolors);
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192 return 0;
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193 }
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194
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195 /* Try to set the gamma ramp in the driver */
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196 succeeded = -1;
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197 if ( video->SetGammaRamp ) {
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198 succeeded = video->SetGammaRamp(this, video->gamma);
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199 } else {
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200 SDL_SetError("Gamma ramp manipulation not supported");
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201 }
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202 return succeeded;
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203 }
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204
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205 int SDL_GetGammaRamp(Uint16 *red, Uint16 *green, Uint16 *blue)
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206 {
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207 SDL_VideoDevice *video = current_video;
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208 SDL_VideoDevice *this = current_video;
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209
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210 /* Lazily allocate the gamma table */
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211 if ( ! video->gamma ) {
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212 video->gamma = malloc(3*256*sizeof(*video->gamma));
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213 if ( ! video->gamma ) {
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214 SDL_OutOfMemory();
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215 return -1;
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216 }
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217 if ( video->GetGammaRamp ) {
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218 /* Get the real hardware gamma */
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219 video->GetGammaRamp(this, video->gamma);
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220 } else {
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221 /* Assume an identity gamma */
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222 int i;
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223 for ( i=0; i<256; ++i ) {
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224 video->gamma[0*256+i] = (i << 8) | i;
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225 video->gamma[1*256+i] = (i << 8) | i;
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226 video->gamma[2*256+i] = (i << 8) | i;
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227 }
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228 }
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229 }
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230
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231 /* Just copy from our internal table */
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232 if ( red ) {
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233 memcpy(red, &video->gamma[0*256], 256*sizeof(*red));
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234 }
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235 if ( green ) {
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236 memcpy(green, &video->gamma[1*256], 256*sizeof(*green));
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237 }
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238 if ( blue ) {
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239 memcpy(blue, &video->gamma[2*256], 256*sizeof(*blue));
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240 }
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241 return 0;
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242 }
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