/* DualPipeHDRPipe1_FormattingShader.frag.txt -- Low byte image output formatter
 *
 * This shader is intended for use as a plugin for the 'FinalOutputFormattingBlit1'
 * chain of the Psychtoolbox-3 imaging pipeline.
 *
 * (c)2009 by Mario Kleiner, part of PTB-3, licensed to you under MIT license.
 * See file License.txt in the Psychtoolbox root folder for the license.
 *
 */

#extension GL_ARB_texture_rectangle : enable

uniform sampler2DRect Image;

/* Declare external function for color conversion: */
vec4 icmTransformColor(vec4 incolor);

void main()
{
    /* Get default texel read position (x,y): x is column, y is row of image. */
    vec2 readpos = gl_FragCoord.xy;

    /* Retrieve RGBA HDR input color value for pixel. */
    vec4 incolor = texture2DRect(Image, readpos);

    /* Apply some color transformation (clamping, gamma correction etc.): */
/*  Not yet implemented:   incolor = icmTransformColor(incolor); */

    /* Remap all color channels from 0.0 - 1.0 to 0 to 65535: */
    /* Perform rounding for non-integral numbers and add a small epsilon to take numeric roundoff into account: */
    vec3 index = floor(incolor.rgb * 65535.0 + 0.5) + 0.01;

    /* Compute low bytes (8 LSBs) for color components. */
    vec3 lowbytes = mod(index, 256.0) / 255.0;

    /* Output low byte into framebuffer pixel: */
    gl_FragColor.rgb = lowbytes;

    /* Fix alpha channel to 1.0. */
    gl_FragColor.a = 1.0;
}