/* SPDX-License-Identifier: BSD-2-Clause */
/*
From http://jgt.akpeters.com/papers/McGuire08/

Efficient, High-Quality Bayer Demosaic Filtering on GPUs

Morgan McGuire

This paper appears in issue Volume 13, Number 4.
---------------------------------------------------------
Copyright (c) 2008, Morgan McGuire. All rights reserved.
*/

//Vertex Shader


/** (w,h,1/w,1/h) */
uniform vec4            sourceSize;

/** Pixel position of the first red pixel in the */
/**  Bayer pattern.  [{0,1}, {0, 1}]*/
uniform vec2            firstRed;

/** .xy = Pixel being sampled in the fragment shader on the range [0, 1]
    .zw = ...on the range [0, sourceSize], offset by firstRed */
varying vec4            center;

/** center.x + (-2/w, -1/w, 1/w, 2/w); These are the x-positions */
/** of the adjacent pixels.*/
varying vec4            xCoord;

/** center.y + (-2/h, -1/h, 1/h, 2/h); These are the y-positions */
/** of the adjacent pixels.*/
varying vec4            yCoord;

void main(void) {
    center.xy = gl_MultiTexCoord0.xy;
    center.zw = gl_MultiTexCoord0.xy * sourceSize.xy + firstRed;

    vec2 invSize = sourceSize.zw;
    xCoord = center.x + vec4(-2.0 * invSize.x,
                             -invSize.x, invSize.x, 2.0 * invSize.x);
    yCoord = center.y + vec4(-2.0 * invSize.y,
                              -invSize.y, invSize.y, 2.0 * invSize.y);

    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}