/*
 * Copyright (C) 2006 Oliver Hunt <ojh16@student.canterbury.ac.nz>.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */
 
/*
 * Performs the transformation:
 * P'(x,y) <- P( x + scale * (XC(x,y) - .5), y + scale * (YC(x,y) - .5))
 *
 * x/ychannel arguments are used to select the appropriate channel for x and
 * y displacement.  Hence each vector should have only one non-zero element,
 * which should have the value 1.0.
 *
 */

kernel vec4 displacementMap(sampler image, sampler map, vec4 xchannel, vec4 ychannel, float scale)
{
    vec2 samplePos = samplerCoord(image);
    vec4 XCYC = sample(map, samplerCoord(map));
    float xc = dot(XCYC, xchannel);
    float yc = dot(XCYC, ychannel);
    samplePos.x += scale*(xc-0.5);
    //flip the y-axis
    samplePos.y -= scale*(yc-0.5);
    return sample(image, samplePos);
}
