SDL_gamma.c
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/*
SDL - Simple DirectMedia Layer
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Copyright (C) 1997-2006 Sam Lantinga
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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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
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Lesser General Public License for more details.
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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
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Sam Lantinga
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slouken@libsdl.org
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*/
/* Gamma correction support */
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#include "SDL_config.h"
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#ifdef HAVE_MATH_H
#include <math.h> /* Used for calculating gamma ramps */
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#else
/* Math routines from uClibc: http://www.uclibc.org */
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#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
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#include "SDL_stdlib.h"
#include "SDL_string.h"
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#include "SDL_error.h"
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#include "SDL_sysvideo.h"
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static void CalculateGammaRamp(float gamma, Uint16 *ramp)
{
int i;
/* 0.0 gamma is all black */
if ( gamma <= 0.0 ) {
for ( i=0; i<256; ++i ) {
ramp[i] = 0;
}
return;
} else
/* 1.0 gamma is identity */
if ( gamma == 1.0 ) {
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 = 0.0;
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 ) {
*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;
}
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int SDL_SetGammaRamp(const Uint16 *red, const Uint16 *green, const Uint16 *blue)
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{
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 ) {
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SDL_memcpy(&video->gamma[0*256], red, 256*sizeof(*video->gamma));
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}
if ( green ) {
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SDL_memcpy(&video->gamma[1*256], green, 256*sizeof(*video->gamma));
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}
if ( blue ) {
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SDL_memcpy(&video->gamma[2*256], blue, 256*sizeof(*video->gamma));
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}
/* 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 ) {
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video->gamma = SDL_malloc(3*256*sizeof(*video->gamma));
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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 ) {
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SDL_memcpy(red, &video->gamma[0*256], 256*sizeof(*red));
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}
if ( green ) {
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SDL_memcpy(green, &video->gamma[1*256], 256*sizeof(*green));
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}
if ( blue ) {
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SDL_memcpy(blue, &video->gamma[2*256], 256*sizeof(*blue));
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}
return 0;
}