xash3d-fwgs/engine/common/gamma.c

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/*
gamma.c - gamma routines
Copyright (C) 2011 Uncle Mike
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
*/
#include "common.h"
#include <mathlib.h>
#include "gl_local.h"
//-----------------------------------------------------------------------------
// Gamma conversion support
//-----------------------------------------------------------------------------
static byte texgammatable[256]; // palette is sent through this to convert to screen gamma
static byte lightgammatable[256];
static int lineargammatable[1024];
static int screengammatable[1024];
void BuildGammaTable( float lightgamma, float brightness )
{
int i, inf;
float f, g, g1, g3;
lightgamma = bound( 1.8f, lightgamma, 3.0f );
brightness = bound( 0.0f, brightness, 10.0f );
if( brightness <= 0.0f )
g3 = 0.125f;
else if( brightness > 1.0f )
g3 = 0.05f;
else g3 = 0.125f - (brightness * brightness) * 0.075f;
g = 1.0f / lightgamma;
g1 = GAMMA * g;
for( i = 0; i < 256; i++ )
{
f = pow( i / 255.f, GAMMA );
// scale up
if( brightness > 1.0f )
f = f * brightness;
// shift up
if( f <= g3 ) f = (f / g3) * 0.125f;
else f = 0.125f + ((f - g3) / (1.0f - g3)) * 0.875f;
// convert linear space to desired gamma space
inf = (int)( 255.0 * pow( f, g ));
lightgammatable[i] = bound( 0, inf, 255 );
}
for( i = 0; i < 256; i++ )
{
f = 255.0 * pow(( float )i / 255.0f, TEXGAMMA );
inf = (int)(f + 0.5f);
texgammatable[i] = bound( 0, inf, 255 );
}
for( i = 0; i < 1024; i++ )
{
// convert from screen gamma space to linear space
lineargammatable[i] = 1023 * pow( i / 1023.0, g1 );
// convert from linear gamma space to screen space
screengammatable[i] = 1023 * pow( i / 1023.0, 1.0 / g1 );
}
}
byte LightToTexGamma( byte b )
{
return lightgammatable[b];
}
byte TextureToGamma( byte b )
{
return texgammatable[b];
}