text: /*
      SDL - Simple DirectMedia Layer
      Copyright (C) 1997-2009 Sam Lantinga
  
      This library is free software; you can redistribute it and/or
      modify it under the terms of the GNU Lesser General Public
      License as published by the Free Software Foundation; either
      version 2.1 of the License, or (at your option) any later version.
  
      This library is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      Lesser General Public License for more details.
  
      You should have received a copy of the GNU Lesser General Public
      License along with this library; if not, write to the Free Software
      Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  
      Sam Lantinga
      slouken@libsdl.org
  */
  #include "SDL_config.h"
  
  /* Gamma correction support */
  
  #ifdef HAVE_MATH_H
  #include <math.h>	/* Used for calculating gamma ramps */
  #else
  /* Math routines from uClibc: http://www.uclibc.org */
  #include "math_private.h"
  #include "e_sqrt.h"
  #include "e_pow.h"
  #include "e_log.h"
  #define pow(x, y)	__ieee754_pow(x, y)
  #define log(x)		__ieee754_log(x)
  #endif
  
  #include "SDL_sysvideo.h"
  
  
  static void CalculateGammaRamp(float gamma, Uint16 *ramp)
  {
  	int i;
  
  	/* 0.0 gamma is all black */
  	if ( gamma <= 0.0f ) {
  		for ( i=0; i<256; ++i ) {
  			ramp[i] = 0;
  		}
  		return;
  	} else
  	/* 1.0 gamma is identity */
  	if ( gamma == 1.0f ) {
  		for ( i=0; i<256; ++i ) {
  			ramp[i] = (i << 8) | i;
  		}
  		return;
  	} else
  	/* Calculate a real gamma ramp */
  	{ int value;
  		gamma = 1.0f / gamma;
  		for ( i=0; i<256; ++i ) {
  			value = (int)(pow((double)i/256.0, gamma)*65535.0+0.5);
  			if ( value > 65535 ) {
  				value = 65535;
  			}
  			ramp[i] = (Uint16)value;
  		}
  	}
  }
  static void CalculateGammaFromRamp(float *gamma, Uint16 *ramp)
  {
  	/* The following is adapted from a post by Garrett Bass on OpenGL
  	   Gamedev list, March 4, 2000.
  	 */
  	float sum = 0.0f;
  	int i, count = 0;
  
  	*gamma = 1.0;
  	for ( i = 1; i < 256; ++i ) {
  	    if ( (ramp[i] != 0) && (ramp[i] != 65535) ) {
  	        double B = (double)i / 256.0;
  	        double A = ramp[i] / 65535.0;
  	        sum += (float) ( log(A) / log(B) );
  	        count++;
  	    }
  	}
  	if ( count && sum > 0.0f ) {
  		*gamma = 1.0f / (sum / count);
  	}
  }
  
  int SDL_SetGamma(float red, float green, float blue)
  {
  	int succeeded;
  	SDL_VideoDevice *video = current_video;
  	SDL_VideoDevice *this  = current_video;	
  
  	succeeded = -1;
  	/* Prefer using SetGammaRamp(), as it's more flexible */
  	{
  		Uint16 ramp[3][256];
  
  		CalculateGammaRamp(red, ramp[0]);
  		CalculateGammaRamp(green, ramp[1]);
  		CalculateGammaRamp(blue, ramp[2]);
  		succeeded = SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
  	}
  	if ( (succeeded < 0) && video->SetGamma ) {
  		SDL_ClearError();
  		succeeded = video->SetGamma(this, red, green, blue);
  	}
  	return succeeded;
  }
  
  /* Calculating the gamma by integrating the gamma ramps isn't exact,
     so this function isn't officially supported.
  */
  int SDL_GetGamma(float *red, float *green, float *blue)
  {
  	int succeeded;
  	SDL_VideoDevice *video = current_video;
  	SDL_VideoDevice *this  = current_video;	
  
  	succeeded = -1;
  	/* Prefer using GetGammaRamp(), as it's more flexible */
  	{
  		Uint16 ramp[3][256];
  
  		succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
  		if ( succeeded >= 0 ) {
  			CalculateGammaFromRamp(red, ramp[0]);
  			CalculateGammaFromRamp(green, ramp[1]);
  			CalculateGammaFromRamp(blue, ramp[2]);
  		}
  	}
  	if ( (succeeded < 0) && video->GetGamma ) {
  		SDL_ClearError();
  		succeeded = video->GetGamma(this, red, green, blue);
  	}
  	return succeeded;
  }
  
  int SDL_SetGammaRamp(const Uint16 *red, const Uint16 *green, const Uint16 *blue)
  {
  	int succeeded;
  	SDL_VideoDevice *video = current_video;
  	SDL_VideoDevice *this  = current_video;	
  	SDL_Surface *screen = SDL_PublicSurface;
  
  	/* Verify the screen parameter */
  	if ( !screen ) {
  		SDL_SetError("No video mode has been set");
  		return -1;
  	}
  
  	/* Lazily allocate the gamma tables */
  	if ( ! video->gamma ) {
  		SDL_GetGammaRamp(0, 0, 0);
  	}
  
  	/* Fill the gamma table with the new values */
  	if ( red ) {
  		SDL_memcpy(&video->gamma[0*256], red, 256*sizeof(*video->gamma));
  	}
  	if ( green ) {
  		SDL_memcpy(&video->gamma[1*256], green, 256*sizeof(*video->gamma));
  	}
  	if ( blue ) {
  		SDL_memcpy(&video->gamma[2*256], blue, 256*sizeof(*video->gamma));
  	}
  
  	/* Gamma correction always possible on split palettes */
  	if ( (screen->flags & SDL_HWPALETTE) == SDL_HWPALETTE ) {
  		SDL_Palette *pal = screen->format->palette;
  
  		/* If physical palette has been set independently, use it */
  		if(video->physpal)
  		        pal = video->physpal;
  		      
  		SDL_SetPalette(screen, SDL_PHYSPAL,
  			       pal->colors, 0, pal->ncolors);
  		return 0;
  	}
  
  	/* Try to set the gamma ramp in the driver */
  	succeeded = -1;
  	if ( video->SetGammaRamp ) {
  		succeeded = video->SetGammaRamp(this, video->gamma);
  	} else {
  		SDL_SetError("Gamma ramp manipulation not supported");
  	}
  	return succeeded;
  }
  
  int SDL_GetGammaRamp(Uint16 *red, Uint16 *green, Uint16 *blue)
  {
  	SDL_VideoDevice *video = current_video;
  	SDL_VideoDevice *this  = current_video;	
  
  	/* Lazily allocate the gamma table */
  	if ( ! video->gamma ) {
  		video->gamma = SDL_malloc(3*256*sizeof(*video->gamma));
  		if ( ! video->gamma ) {
  			SDL_OutOfMemory();
  			return -1;
  		}
  		if ( video->GetGammaRamp ) {
  			/* Get the real hardware gamma */
  			video->GetGammaRamp(this, video->gamma);
  		} else {
  			/* Assume an identity gamma */
  			int i;
  			for ( i=0; i<256; ++i ) {
  				video->gamma[0*256+i] = (i << 8) | i;
  				video->gamma[1*256+i] = (i << 8) | i;
  				video->gamma[2*256+i] = (i << 8) | i;
  			}
  		}
  	}
  
  	/* Just copy from our internal table */
  	if ( red ) {
  		SDL_memcpy(red, &video->gamma[0*256], 256*sizeof(*red));
  	}
  	if ( green ) {
  		SDL_memcpy(green, &video->gamma[1*256], 256*sizeof(*green));
  	}
  	if ( blue ) {
  		SDL_memcpy(blue, &video->gamma[2*256], 256*sizeof(*blue));
  	}
  	return 0;
  }
  