/// ============================================================================
/*
Copyright (C) 2005 Robert Beckebans <trebor_7@users.sourceforge.net>
Please see the file "AUTHORS" for a list of contributors

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 2
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.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/
/// ============================================================================

uniform sampler2D	u_ColorMap;
uniform vec2		u_FBufScale;
uniform vec2		u_NPotScale;

const vec4 gloomStart = vec4(0.95,0.95,0.95,0.95);
float sqr(float x) { return x*x; }
vec4 sqr(vec4 x) { return x*x; }
vec4 expand_luminance(vec4 color)
{
	return color*(sqr(color.a*2.0)+1.0);
} 

void	main()
{
	vec2 st00 = gl_FragCoord.st;

	// calculate the screen texcoord in the 0.0 to 1.0 range
	st00 *= u_FBufScale;
	
	// scale by the screen non-power-of-two-adjust
	st00 *= u_NPotScale;
	
	// calculate luminance
	vec4 color = texture2D(u_ColorMap, st00);
	gl_FragColor = expand_luminance(color)-gloomStart;
}