/*

 * 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);

}