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  1. /*
  2.     SDL - Simple DirectMedia Layer
  3.     Copyright (C) 1997, 1998, 1999, 2000, 2001  Sam Lantinga
  4.  
  5.     This library is free software; you can redistribute it and/or
  6.     modify it under the terms of the GNU Library General Public
  7.     License as published by the Free Software Foundation; either
  8.     version 2 of the License, or (at your option) any later version.
  9.  
  10.     This library is distributed in the hope that it will be useful,
  11.     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12.     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13.     Library General Public License for more details.
  14.  
  15.     You should have received a copy of the GNU Library General Public
  16.     License along with this library; if not, write to the Free
  17.     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18.  
  19.     Sam Lantinga
  20.     slouken@devolution.com
  21. */
  22.  
  23.  
  24. /* Gamma correction support */
  25.  
  26. #define USE_MATH_H      /* Used for calculating gamma ramps */
  27.  
  28. #ifdef USE_MATH_H
  29. #include <math.h>
  30. #endif
  31. #include <stdlib.h>
  32.  
  33. #include "SDL_error.h"
  34. #include "SDL_sysvideo.h"
  35.  
  36. #ifdef USE_MATH_H
  37. static void CalculateGammaRamp(float gamma, Uint16 *ramp)
  38. {
  39.         int i;
  40.  
  41.         /* 0.0 gamma is all black */
  42.         if ( gamma <= 0.0 ) {
  43.                 for ( i=0; i<256; ++i ) {
  44.                         ramp[i] = 0;
  45.                 }
  46.                 return;
  47.         } else
  48.         /* 1.0 gamma is identity */
  49.         if ( gamma == 1.0 ) {
  50.                 for ( i=0; i<256; ++i ) {
  51.                         ramp[i] = (i << 8) | i;
  52.                 }
  53.                 return;
  54.         } else
  55.         /* Calculate a real gamma ramp */
  56.         { int value;
  57.                 gamma = 1.0f / gamma;
  58.                 for ( i=0; i<256; ++i ) {
  59.                         value = (int)(pow((double)i/256.0, gamma)*65535.0+0.5);
  60.                         if ( value > 65535 ) {
  61.                                 value = 65535;
  62.                         }
  63.                         ramp[i] = (Uint16)value;
  64.                 }
  65.         }
  66. }
  67. static void CalculateGammaFromRamp(float *gamma, Uint16 *ramp)
  68. {
  69.         /* The following is adapted from a post by Garrett Bass on OpenGL
  70.            Gamedev list, March 4, 2000.
  71.          */
  72.         float sum = 0.0;
  73.         int i, count = 0;
  74.  
  75.         *gamma = 1.0;
  76.         for ( i = 1; i < 256; ++i ) {
  77.             if ( (ramp[i] != 0) && (ramp[i] != 65535) ) {
  78.                 double B = (double)i / 256.0;
  79.                 double A = ramp[i] / 65535.0;
  80.                 sum += (float) ( log(A) / log(B) );
  81.                 count++;
  82.             }
  83.         }
  84.         if ( count && sum ) {
  85.                 *gamma = 1.0f / (sum / count);
  86.         }
  87. }
  88. #endif /* USE_MATH_H */
  89.  
  90. int SDL_SetGamma(float red, float green, float blue)
  91. {
  92.         int succeeded;
  93.         SDL_VideoDevice *video = current_video;
  94.         SDL_VideoDevice *this  = current_video;
  95.  
  96.         succeeded = -1;
  97. #ifdef USE_MATH_H
  98.         /* Prefer using SetGammaRamp(), as it's more flexible */
  99.         {
  100.                 Uint16 ramp[3][256];
  101.  
  102.                 CalculateGammaRamp(red, ramp[0]);
  103.                 CalculateGammaRamp(green, ramp[1]);
  104.                 CalculateGammaRamp(blue, ramp[2]);
  105.                 succeeded = SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
  106.         }
  107. #else
  108.         SDL_SetError("Gamma correction not supported");
  109. #endif
  110.         if ( (succeeded < 0) && video->SetGamma ) {
  111.                 SDL_ClearError();
  112.                 succeeded = video->SetGamma(this, red, green, blue);
  113.         }
  114.         return succeeded;
  115. }
  116.  
  117. /* Calculating the gamma by integrating the gamma ramps isn't exact,
  118.    so this function isn't officially supported.
  119. */
  120. int SDL_GetGamma(float *red, float *green, float *blue)
  121. {
  122.         int succeeded;
  123.         SDL_VideoDevice *video = current_video;
  124.         SDL_VideoDevice *this  = current_video;
  125.  
  126.         succeeded = -1;
  127. #ifdef USE_MATH_H
  128.         /* Prefer using GetGammaRamp(), as it's more flexible */
  129.         {
  130.                 Uint16 ramp[3][256];
  131.  
  132.                 succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
  133.                 if ( succeeded >= 0 ) {
  134.                         CalculateGammaFromRamp(red, ramp[0]);
  135.                         CalculateGammaFromRamp(green, ramp[1]);
  136.                         CalculateGammaFromRamp(blue, ramp[2]);
  137.                 }
  138.         }
  139. #else
  140.         SDL_SetError("Gamma correction not supported");
  141. #endif
  142.         if ( (succeeded < 0) && video->GetGamma ) {
  143.                 SDL_ClearError();
  144.                 succeeded = video->GetGamma(this, red, green, blue);
  145.         }
  146.         return succeeded;
  147. }
  148.  
  149. int SDL_SetGammaRamp(Uint16 *red, Uint16 *green, Uint16 *blue)
  150. {
  151.         int succeeded;
  152.         SDL_VideoDevice *video = current_video;
  153.         SDL_VideoDevice *this  = current_video;
  154.         SDL_Surface *screen = SDL_PublicSurface;
  155.  
  156.         /* Verify the screen parameter */
  157.         if ( !screen ) {
  158.                 SDL_SetError("No video mode has been set");
  159.                 return -1;
  160.         }
  161.  
  162.         /* Lazily allocate the gamma tables */
  163.         if ( ! video->gamma ) {
  164.                 SDL_GetGammaRamp(0, 0, 0);
  165.         }
  166.  
  167.         /* Fill the gamma table with the new values */
  168.         if ( red ) {
  169.                 memcpy(&video->gamma[0*256], red, 256*sizeof(*video->gamma));
  170.         }
  171.         if ( green ) {
  172.                 memcpy(&video->gamma[1*256], green, 256*sizeof(*video->gamma));
  173.         }
  174.         if ( blue ) {
  175.                 memcpy(&video->gamma[2*256], blue, 256*sizeof(*video->gamma));
  176.         }
  177.  
  178.         /* Gamma correction always possible on split palettes */
  179.         if ( (screen->flags & SDL_HWPALETTE) == SDL_HWPALETTE ) {
  180.                 SDL_Palette *pal = screen->format->palette;
  181.  
  182.                 /* If physical palette has been set independently, use it */
  183.                 if(video->physpal)
  184.                         pal = video->physpal;
  185.                      
  186.                 SDL_SetPalette(screen, SDL_PHYSPAL,
  187.                                pal->colors, 0, pal->ncolors);
  188.                 return 0;
  189.         }
  190.  
  191.         /* Try to set the gamma ramp in the driver */
  192.         succeeded = -1;
  193.         if ( video->SetGammaRamp ) {
  194.                 succeeded = video->SetGammaRamp(this, video->gamma);
  195.         } else {
  196.                 SDL_SetError("Gamma ramp manipulation not supported");
  197.         }
  198.         return succeeded;
  199. }
  200.  
  201. int SDL_GetGammaRamp(Uint16 *red, Uint16 *green, Uint16 *blue)
  202. {
  203.         SDL_VideoDevice *video = current_video;
  204.         SDL_VideoDevice *this  = current_video;
  205.  
  206.         /* Lazily allocate the gamma table */
  207.         if ( ! video->gamma ) {
  208.                 video->gamma = malloc(3*256*sizeof(*video->gamma));
  209.                 if ( ! video->gamma ) {
  210.                         SDL_OutOfMemory();
  211.                         return -1;
  212.                 }
  213.                 if ( video->GetGammaRamp ) {
  214.                         /* Get the real hardware gamma */
  215.                         video->GetGammaRamp(this, video->gamma);
  216.                 } else {
  217.                         /* Assume an identity gamma */
  218.                         int i;
  219.                         for ( i=0; i<256; ++i ) {
  220.                                 video->gamma[0*256+i] = (i << 8) | i;
  221.                                 video->gamma[1*256+i] = (i << 8) | i;
  222.                                 video->gamma[2*256+i] = (i << 8) | i;
  223.                         }
  224.                 }
  225.         }
  226.  
  227.         /* Just copy from our internal table */
  228.         if ( red ) {
  229.                 memcpy(red, &video->gamma[0*256], 256*sizeof(*red));
  230.         }
  231.         if ( green ) {
  232.                 memcpy(green, &video->gamma[1*256], 256*sizeof(*green));
  233.         }
  234.         if ( blue ) {
  235.                 memcpy(blue, &video->gamma[2*256], 256*sizeof(*blue));
  236.         }
  237.         return 0;
  238. }
  239.