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