colors.js

/*jslint sloppy: true, white: true */
var toDegree = 180 / Math.PI;
function fromArgb(a, r, g, b) {
    return 'rgba(' + r + ', ' + g + ', ' + b + ', ' + a/255 + ')';
}
function convertHsvToRgb(h, s, v) {
    var a, b, c, d, hueFloor;
    h = h / 360;
    if (s > 0) {
        if (h >= 1) {
            h = 0;
        }
        h = 6 * h;
        hueFloor = Math.floor(h);
        a = Math.round(255 * v * (1.0 - s));
        b = Math.round(255 * v * (1.0 - (s * (h - hueFloor))));
        c = Math.round(255 * v * (1.0 - (s * (1.0 - (h - hueFloor)))));
        d = Math.round(255 * v);

        switch (hueFloor) {
            case 0: return fromArgb(255, d, c, a);
            case 1: return fromArgb(255, b, d, a);
            case 2: return fromArgb(255, a, d, c);
            case 3: return fromArgb(255, a, b, d);
            case 4: return fromArgb(255, c, a, d);
            case 5: return fromArgb(255, d, a, b);
            default: return fromArgb(0, 0, 0, 0);
        } 
    }
    d = v * 255;
    return fromArgb(255, d, d, d);
}

function getColor(x, y) {
    var hue = Math.atan2(y, x) * toDegree + 360;
    return convertHsvToRgb(hue, 1, 1);
}