/* Shader for applying a bias and scale factor to a rectangle texture during drawing.
 * Can be used to apply f(g)=(g + prescaleoffset)*scalefactor + postscaleoffset;
 * (w)2006 by Mario Kleiner. Licensed under MIT license.
*/

#extension GL_ARB_texture_rectangle : enable

/* We currently only support rectangular textures: */
uniform sampler2DRect Image;

uniform float prescaleoffset;
uniform float postscaleoffset;
uniform float scalefactor;

void main()
{
    vec4 incolor = texture2DRect(Image, gl_TexCoord[0].st);
    /* Just pass-through the alpha value, do not modify it: */
    gl_FragColor.a = incolor.a;
    /* Apply mapping to RGB channels... */
    gl_FragColor.rgb = ((incolor.rgb + vec3(prescaleoffset)) * scalefactor) + vec3(postscaleoffset);
}