/*
 * File: SquareWaveApertureShader.frag.txt 
 * Shader for drawing of basic parameterized square wave grating patches.
 * Applies a circular aperture of radius 'Radius'.
 *
 * Copyright 2011, Ian Andolina <http://github.com/iandol>, licenced under the MIT Licence
 *
 */

uniform float Radius;
uniform vec2  Center;

uniform vec4 Offset;

float Dist;

varying vec4  baseColor;
varying float Phase;
varying float FreqTwoPi;

void main()
{
    /* Query current output texel position: */
    vec2 pos = gl_TexCoord[0].xy;

    /* find our distance from center */
    Dist = distance(pos, Center);

    /* If distance to center (aka radius of pixel) > Radius, discard this pixel: */
    if (Dist > Radius) discard;

    /* Evaluate sine grating at requested position, frequency and phase: */
    float sv = sin(pos.x * FreqTwoPi + Phase);
    sv = smoothstep(-0.2, 0.2, sv) * 2.0 - 1.0;

    /* Multiply/Modulate base color and alpha with calculated sine          */
    /* values, add some constant color/alpha Offset, assign as final fragment */
    /* output color: */
    gl_FragColor = (baseColor * sv) + Offset;
    gl_FragColor.a = sv;
}