/**
 * Defines a new instance of the rainyday.js.
 * @param options options element with script parameters
 * @param canvas to be used (if not defined a new one will be created)
 */

function RainyDay(options, canvas) {

    if (this === window) { //if *this* is the window object, start over with a *new* object
        return new RainyDay(options);
    }

    this.img = options.image;
    var defaults = {
        opacity: 1,
        blur: 10,
        crop: [0, 0, this.img.naturalWidth, this.img.naturalHeight],
        enableSizeChange: true,
        parentElement: document.getElementsByTagName('body')[0],
        fps: 30,
        fillStyle: '#8ED6FF',
        enableCollisions: true,
        gravityThreshold: 3,
        gravityAngle: Math.PI / 2,
        gravityAngleVariance: 0,
        reflectionScaledownFactor: 5,
        reflectionDropMappingWidth: 200,
        reflectionDropMappingHeight: 200,
        width: this.img.clientWidth,
        height: this.img.clientHeight,
        position: 'absolute',
        top: 0,
        left: 0
    };

    // add the defaults to options
    for (var option in defaults) {
        if (typeof options[option] === 'undefined') {
            options[option] = defaults[option];
        }
    }
    this.options = options;

    this.drops = [];

    // prepare canvas elements
    this.canvas = canvas || this.prepareCanvas();
    this.prepareBackground(this.canvas.width, this.canvas.height);
    this.prepareGlass();

    // assume defaults
    this.reflection = this.REFLECTION_MINIATURE;
    this.trail = this.TRAIL_DROPS;
    this.gravity = this.GRAVITY_NON_LINEAR;
    this.collision = this.COLLISION_SIMPLE;

    // set polyfill of requestAnimationFrame
    this.setRequestAnimFrame();
}

/**
 * Create the main canvas over a given element
 * @returns HTMLElement the canvas
 */
RainyDay.prototype.prepareCanvas = function() {
    var canvas = document.createElement('canvas');
    canvas.style.position = this.options.position;
    canvas.style.top = this.options.top;
    canvas.style.left = this.options.left;
    canvas.width = this.options.width;
    canvas.height = this.options.height;
    this.options.parentElement.appendChild(canvas);
    if (this.enableSizeChange) {
        this.setResizeHandler();
    }
    return canvas;
};

RainyDay.prototype.setResizeHandler = function() {
    // use setInterval if oneresize event already use by other.
    if (window.onresize !== null) {
        window.setInterval(this.checkSize.bind(this), 100);
    } else {
        window.onresize = this.checkSize.bind(this);
        window.onorientationchange = this.checkSize.bind(this);
    }
};

/**
 * Periodically check the size of the underlying element
 */
RainyDay.prototype.checkSize = function() {
    var clientWidth = this.img.clientWidth;
    var clientHeight = this.img.clientHeight;
    var clientOffsetLeft = this.img.offsetLeft;
    var clientOffsetTop = this.img.offsetTop;
    var canvasWidth = this.canvas.width;
    var canvasHeight = this.canvas.height;
    var canvasOffsetLeft = this.canvas.offsetLeft;
    var canvasOffsetTop = this.canvas.offsetTop;

    if (canvasWidth !== clientWidth || canvasHeight !== clientHeight) {
        this.canvas.width = this.canvas.width;
        this.canvas.height = this.canvas.height;
        this.prepareBackground(this.canvas.width, this.canvas.height);
        this.glass.width = this.canvas.width;
        this.glass.height = this.canvas.height;
        this.prepareReflections();
    }
    if (canvasOffsetLeft !== clientOffsetLeft || canvasOffsetTop !== clientOffsetTop) {
        this.canvas.offsetLeft = clientOffsetLeft;
        this.canvas.offsetTop = clientOffsetTop;
    }
};

/**
 * Start animation loop
 */
RainyDay.prototype.animateDrops = function() {
    if (this.addDropCallback) {
        this.addDropCallback();
    }
    // |this.drops| array may be changed as we iterate over drops
    var dropsClone = this.drops.slice();
    var newDrops = [];
    for (var i = 0; i < dropsClone.length; ++i) {
        if (dropsClone[i].animate()) {
            newDrops.push(dropsClone[i]);
        }
    }
    this.drops = newDrops;
    window.requestAnimFrame(this.animateDrops.bind(this));
};

/**
 * Polyfill for requestAnimationFrame
 */
RainyDay.prototype.setRequestAnimFrame = function() {
    var fps = this.options.fps;
    window.requestAnimFrame = (function() {
        return window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            window.mozRequestAnimationFrame ||
            function(callback) {
                window.setTimeout(callback, 1000 / fps);
            };
    })();
};

/**
 * Create the helper canvas for rendering raindrop reflections.
 */
RainyDay.prototype.prepareReflections = function() {
    this.reflected = document.createElement('canvas');
    this.reflected.width = this.canvas.width / this.options.reflectionScaledownFactor;
    this.reflected.height = this.canvas.height / this.options.reflectionScaledownFactor;
    var ctx = this.reflected.getContext('2d');
    ctx.drawImage(this.img, this.options.crop[0], this.options.crop[1], this.options.crop[2], this.options.crop[3], 0, 0, this.reflected.width, this.reflected.height);
};

/**
 * Create the glass canvas.
 */
RainyDay.prototype.prepareGlass = function() {
    this.glass = document.createElement('canvas');
    this.glass.width = this.canvas.width;
    this.glass.height = this.canvas.height;
    this.context = this.glass.getContext('2d');
};

/**
 * Main function for starting rain rendering.
 * @param presets list of presets to be applied
 * @param speed speed of the animation (if not provided or 0 static image will be generated)
 */
RainyDay.prototype.rain = function(presets, speed) {
    // prepare canvas for drop reflections
    if (this.reflection !== this.REFLECTION_NONE) {
        this.prepareReflections();
    }

    this.animateDrops();

    // animation
    this.presets = presets;

    this.PRIVATE_GRAVITY_FORCE_FACTOR_Y = (this.options.fps * 0.001) / 25;
    this.PRIVATE_GRAVITY_FORCE_FACTOR_X = ((Math.PI / 2) - this.options.gravityAngle) * (this.options.fps * 0.001) / 50;

    // prepare gravity matrix
    if (this.options.enableCollisions) {

        // calculate max radius of a drop to establish gravity matrix resolution
        var maxDropRadius = 0;
        for (var i = 0; i < presets.length; i++) {
            if (presets[i][0] + presets[i][1] > maxDropRadius) {
                maxDropRadius = Math.floor(presets[i][0] + presets[i][1]);
            }
        }

        if (maxDropRadius > 0) {
            // initialize the gravity matrix
            var mwi = Math.ceil(this.canvas.width / maxDropRadius);
            var mhi = Math.ceil(this.canvas.height / maxDropRadius);
            this.matrix = new CollisionMatrix(mwi, mhi, maxDropRadius);
        } else {
            this.options.enableCollisions = false;
        }
    }

    for (var i = 0; i < presets.length; i++) {
        if (!presets[i][3]) {
            presets[i][3] = -1;
        }
    }

    var lastExecutionTime = 0;
    this.addDropCallback = function() {
        var timestamp = new Date().getTime();
        if (timestamp - lastExecutionTime < speed) {
            return;
        }
        lastExecutionTime = timestamp;
        var context = this.canvas.getContext('2d');
        context.clearRect(0, 0, this.canvas.width, this.canvas.height);
        context.drawImage(this.background, 0, 0, this.canvas.width, this.canvas.height);
        // select matching preset
        var preset;
        for (var i = 0; i < presets.length; i++) {
            if (presets[i][2] > 1 || presets[i][3] === -1) {
                if (presets[i][3] !== 0) {
                    presets[i][3]--;
                    for (var y = 0; y < presets[i][2]; ++y) {
                        this.putDrop(new Drop(this, Math.random() * this.canvas.width, Math.random() * this.canvas.height, presets[i][0], presets[i][1]));
                    }
                }
            } else if (Math.random() < presets[i][2]) {
                preset = presets[i];
                break;
            }
        }
        if (preset) {
            this.putDrop(new Drop(this, Math.random() * this.canvas.width, Math.random() * this.canvas.height, preset[0], preset[1]));
        }
        context.save();
        context.globalAlpha = this.opacity;
        context.drawImage(this.glass, 0, 0, this.canvas.width, this.canvas.height);
        context.restore();
    }
        .bind(this);
};

/**
 * Adds a new raindrop to the animation.
 * @param drop drop object to be added to the animation
 */
RainyDay.prototype.putDrop = function(drop) {
    drop.draw();
    if (this.gravity && drop.r > this.options.gravityThreshold) {
        if (this.options.enableCollisions) {
            this.matrix.update(drop);
        }
        this.drops.push(drop);
    }
};

/**
 * Clear the drop and remove from the list if applicable.
 * @drop to be cleared
 * @force force removal from the list
 * result if true animation of this drop should be stopped
 */
RainyDay.prototype.clearDrop = function(drop, force) {
    var result = drop.clear(force);
    if (result) {
        var index = this.drops.indexOf(drop);
        if (index >= 0) {
            this.drops.splice(index, 1);
        }
    }
    return result;
};

/**
 * Defines a new raindrop object.
 * @param rainyday reference to the parent object
 * @param centerX x position of the center of this drop
 * @param centerY y position of the center of this drop
 * @param min minimum size of a drop
 * @param base base value for randomizing drop size
 */

function Drop(rainyday, centerX, centerY, min, base) {
    this.x = Math.floor(centerX);
    this.y = Math.floor(centerY);
    this.r = (Math.random() * base) + min;
    this.rainyday = rainyday;
    this.context = rainyday.context;
    this.reflection = rainyday.reflected;
}

/**
 * Draws a raindrop on canvas at the current position.
 */
Drop.prototype.draw = function() {
    this.context.save();
    this.context.beginPath();

    var orgR = this.r;
    this.r = 0.95 * this.r;
    if (this.r < 3) {
        this.context.arc(this.x, this.y, this.r, 0, Math.PI * 2, true);
        this.context.closePath();
    } else if (this.colliding || this.yspeed > 2) {
        if (this.colliding) {
            var collider = this.colliding;
            this.r = 1.001 * (this.r > collider.r ? this.r : collider.r);
            this.x += (collider.x - this.x);
            this.colliding = null;
        }

        var yr = 1 + 0.1 * this.yspeed;
        this.context.moveTo(this.x - this.r / yr, this.y);
        this.context.bezierCurveTo(this.x - this.r, this.y - this.r * 2, this.x + this.r, this.y - this.r * 2, this.x + this.r / yr, this.y);
        this.context.bezierCurveTo(this.x + this.r, this.y + yr * this.r, this.x - this.r, this.y + yr * this.r, this.x - this.r / yr, this.y);
    } else {
        this.context.arc(this.x, this.y, this.r * 0.9, 0, Math.PI * 2, true);
        this.context.closePath();
    }

    this.context.clip();

    this.r = orgR;

    if (this.rainyday.reflection) {
        this.rainyday.reflection(this);
    }

    this.context.restore();
};

/**
 * Clears the raindrop region.
 * @param force force stop
 * @returns Boolean true if the animation is stopped
 */
Drop.prototype.clear = function(force) {
    this.context.clearRect(this.x - this.r - 1, this.y - this.r - 2, 2 * this.r + 2, 2 * this.r + 2);
    if (force) {
        this.terminate = true;
        return true;
    }
    if ((this.y - this.r > this.rainyday.h) || (this.x - this.r > this.rainyday.w) || (this.x + this.r < 0)) {
        // over edge so stop this drop
        return true;
    }
    return false;
};

/**
 * Moves the raindrop to a new position according to the gravity.
 */
Drop.prototype.animate = function() {
    if (this.terminate) {
        return false;
    }
    var stopped = this.rainyday.gravity(this);
    if (!stopped && this.rainyday.trail) {
        this.rainyday.trail(this);
    }
    if (this.rainyday.options.enableCollisions) {
        var collisions = this.rainyday.matrix.update(this, stopped);
        if (collisions) {
            this.rainyday.collision(this, collisions);
        }
    }
    return !stopped || this.terminate;
};

/**
 * TRAIL function: no trail at all
 */
RainyDay.prototype.TRAIL_NONE = function() {
    // nothing going on here
};

/**
 * TRAIL function: trail of small drops (default)
 * @param drop raindrop object
 */
RainyDay.prototype.TRAIL_DROPS = function(drop) {
    if (!drop.trailY || drop.y - drop.trailY >= Math.random() * 100 * drop.r) {
        drop.trailY = drop.y;
        this.putDrop(new Drop(this, drop.x + (Math.random() * 2 - 1) * Math.random(), drop.y - drop.r - 5, Math.ceil(drop.r / 5), 0));
    }
};

/**
 * TRAIL function: trail of unblurred image
 * @param drop raindrop object
 */
RainyDay.prototype.TRAIL_SMUDGE = function(drop) {
    var y = drop.y - drop.r - 3;
    var x = drop.x - drop.r / 2 + (Math.random() * 2);
    if (y < 0 || x < 0) {
        return;
    }
    this.context.drawImage(this.clearbackground, x, y, drop.r, 2, x, y, drop.r, 2);
};

/**
 * GRAVITY function: no gravity at all
 * @returns Boolean true if the animation is stopped
 */
RainyDay.prototype.GRAVITY_NONE = function() {
    return true;
};

/**
 * GRAVITY function: linear gravity
 * @param drop raindrop object
 * @returns Boolean true if the animation is stopped
 */
RainyDay.prototype.GRAVITY_LINEAR = function(drop) {
    if (this.clearDrop(drop)) {
        return true;
    }

    if (drop.yspeed) {
        drop.yspeed += this.PRIVATE_GRAVITY_FORCE_FACTOR_Y * Math.floor(drop.r);
        drop.xspeed += this.PRIVATE_GRAVITY_FORCE_FACTOR_X * Math.floor(drop.r);
    } else {
        drop.yspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_Y;
        drop.xspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_X;
    }

    drop.y += drop.yspeed;
    drop.draw();
    return false;
};

/**
 * GRAVITY function: non-linear gravity (default)
 * @param drop raindrop object
 * @returns Boolean true if the animation is stopped
 */
RainyDay.prototype.GRAVITY_NON_LINEAR = function(drop) {
    if (this.clearDrop(drop)) {
        return true;
    }

    if (drop.collided) {
        drop.collided = false;
        drop.seed = Math.floor(drop.r * Math.random() * this.options.fps);
        drop.skipping = false;
        drop.slowing = false;
    } else if (!drop.seed || drop.seed < 0) {
        drop.seed = Math.floor(drop.r * Math.random() * this.options.fps);
        drop.skipping = drop.skipping === false ? true : false;
        drop.slowing = true;
    }

    drop.seed--;

    if (drop.yspeed) {
        if (drop.slowing) {
            drop.yspeed /= 1.1;
            drop.xspeed /= 1.1;
            if (drop.yspeed < this.PRIVATE_GRAVITY_FORCE_FACTOR_Y) {
                drop.slowing = false;
            }

        } else if (drop.skipping) {
            drop.yspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_Y;
            drop.xspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_X;
        } else {
            drop.yspeed += 1 * this.PRIVATE_GRAVITY_FORCE_FACTOR_Y * Math.floor(drop.r);
            drop.xspeed += 1 * this.PRIVATE_GRAVITY_FORCE_FACTOR_X * Math.floor(drop.r);
        }
    } else {
        drop.yspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_Y;
        drop.xspeed = this.PRIVATE_GRAVITY_FORCE_FACTOR_X;
    }

    if (this.options.gravityAngleVariance !== 0) {
        drop.xspeed += ((Math.random() * 2 - 1) * drop.yspeed * this.options.gravityAngleVariance);
    }

    drop.y += drop.yspeed;
    drop.x += drop.xspeed;

    drop.draw();
    return false;
};

/**
 * Utility function to return positive min value
 * @param val1 first number
 * @param val2 second number
 */
RainyDay.prototype.positiveMin = function(val1, val2) {
    var result = 0;
    if (val1 < val2) {
        if (val1 <= 0) {
            result = val2;
        } else {
            result = val1;
        }
    } else {
        if (val2 <= 0) {
            result = val1;
        } else {
            result = val2;
        }
    }
    return result <= 0 ? 1 : result;
};

/**
 * REFLECTION function: no reflection at all
 */
RainyDay.prototype.REFLECTION_NONE = function() {
    this.context.fillStyle = this.options.fillStyle;
    this.context.fill();
};

/**
 * REFLECTION function: miniature reflection (default)
 * @param drop raindrop object
 */
RainyDay.prototype.REFLECTION_MINIATURE = function(drop) {
    var sx = Math.max((drop.x - this.options.reflectionDropMappingWidth) / this.options.reflectionScaledownFactor, 0);
    var sy = Math.max((drop.y - this.options.reflectionDropMappingHeight) / this.options.reflectionScaledownFactor, 0);
    var sw = this.positiveMin(this.options.reflectionDropMappingWidth * 2 / this.options.reflectionScaledownFactor, this.reflected.width - sx);
    var sh = this.positiveMin(this.options.reflectionDropMappingHeight * 2 / this.options.reflectionScaledownFactor, this.reflected.height - sy);
    var dx = Math.max(drop.x - 1.1 * drop.r, 0);
    var dy = Math.max(drop.y - 1.1 * drop.r, 0);
    this.context.drawImage(this.reflected, sx, sy, sw, sh, dx, dy, drop.r * 2, drop.r * 2);
};

/**
 * COLLISION function: default collision implementation
 * @param drop one of the drops colliding
 * @param collisions list of potential collisions
 */
RainyDay.prototype.COLLISION_SIMPLE = function(drop, collisions) {
    var item = collisions;
    var drop2;
    while (item != null) {
        var p = item.drop;
        if (Math.sqrt(Math.pow(drop.x - p.x, 2) + Math.pow(drop.y - p.y, 2)) < (drop.r + p.r)) {
            drop2 = p;
            break;
        }
        item = item.next;
    }

    if (!drop2) {
        return;
    }

    // rename so that we're dealing with low/high drops
    var higher,
        lower;
    if (drop.y > drop2.y) {
        higher = drop;
        lower = drop2;
    } else {
        higher = drop2;
        lower = drop;
    }

    this.clearDrop(lower);
    // force stopping the second drop
    this.clearDrop(higher, true);
    this.matrix.remove(higher);
    lower.draw();

    lower.colliding = higher;
    lower.collided = true;
};

/**
 * Resizes canvas, draws original image and applies blurring algorithm.
 */
RainyDay.prototype.prepareBackground = function() {
    this.background = document.createElement('canvas');
    this.background.width = this.canvas.width;
    this.background.height = this.canvas.height;

    this.clearbackground = document.createElement('canvas');
    this.clearbackground.width = this.canvas.width;
    this.clearbackground.height = this.canvas.height;

    var context = this.background.getContext('2d');
    context.clearRect(0, 0, this.canvas.width, this.canvas.height);

    context.drawImage(this.img, this.options.crop[0], this.options.crop[1], this.options.crop[2], this.options.crop[3], 0, 0, this.canvas.width, this.canvas.height);

    context = this.clearbackground.getContext('2d');
    context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    context.drawImage(this.img, this.options.crop[0], this.options.crop[1], this.options.crop[2], this.options.crop[3], 0, 0, this.canvas.width, this.canvas.height);

    if (!isNaN(this.options.blur) && this.options.blur >= 1) {
        this.stackBlurCanvasRGB(this.canvas.width, this.canvas.height, this.options.blur);
    }
};

/**
 * Implements the Stack Blur Algorithm (@see http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html).
 * @param width width of the canvas
 * @param height height of the canvas
 * @param radius blur radius
 */
RainyDay.prototype.stackBlurCanvasRGB = function(width, height, radius) {

    var shgTable = [
        [0, 9],
        [1, 11],
        [2, 12],
        [3, 13],
        [5, 14],
        [7, 15],
        [11, 16],
        [15, 17],
        [22, 18],
        [31, 19],
        [45, 20],
        [63, 21],
        [90, 22],
        [127, 23],
        [181, 24]
    ];

    var mulTable = [
        512, 512, 456, 512, 328, 456, 335, 512, 405, 328, 271, 456, 388, 335, 292, 512,
        454, 405, 364, 328, 298, 271, 496, 456, 420, 388, 360, 335, 312, 292, 273, 512,
        482, 454, 428, 405, 383, 364, 345, 328, 312, 298, 284, 271, 259, 496, 475, 456,
        437, 420, 404, 388, 374, 360, 347, 335, 323, 312, 302, 292, 282, 273, 265, 512,
        497, 482, 468, 454, 441, 428, 417, 405, 394, 383, 373, 364, 354, 345, 337, 328,
        320, 312, 305, 298, 291, 284, 278, 271, 265, 259, 507, 496, 485, 475, 465, 456,
        446, 437, 428, 420, 412, 404, 396, 388, 381, 374, 367, 360, 354, 347, 341, 335,
        329, 323, 318, 312, 307, 302, 297, 292, 287, 282, 278, 273, 269, 265, 261, 512,
        505, 497, 489, 482, 475, 468, 461, 454, 447, 441, 435, 428, 422, 417, 411, 405,
        399, 394, 389, 383, 378, 373, 368, 364, 359, 354, 350, 345, 341, 337, 332, 328,
        324, 320, 316, 312, 309, 305, 301, 298, 294, 291, 287, 284, 281, 278, 274, 271,
        268, 265, 262, 259, 257, 507, 501, 496, 491, 485, 480, 475, 470, 465, 460, 456,
        451, 446, 442, 437, 433, 428, 424, 420, 416, 412, 408, 404, 400, 396, 392, 388,
        385, 381, 377, 374, 370, 367, 363, 360, 357, 354, 350, 347, 344, 341, 338, 335,
        332, 329, 326, 323, 320, 318, 315, 312, 310, 307, 304, 302, 299, 297, 294, 292,
        289, 287, 285, 282, 280, 278, 275, 273, 271, 269, 267, 265, 263, 261, 259
    ];

    radius |= 0;

    var context = this.background.getContext('2d');
    var imageData = context.getImageData(0, 0, width, height);
    var pixels = imageData.data;
    var x,
        y,
        i,
        p,
        yp,
        yi,
        yw,
        rSum,
        gSum,
        bSum,
        rOutSum,
        gOutSum,
        bOutSum,
        rInSum,
        gInSum,
        bInSum,
        pr,
        pg,
        pb,
        rbs;
    var radiusPlus1 = radius + 1;
    var sumFactor = radiusPlus1 * (radiusPlus1 + 1) / 2;

    var stackStart = new BlurStack();
    var stackEnd = new BlurStack();
    var stack = stackStart;
    for (i = 1; i < 2 * radius + 1; i++) {
        stack = stack.next = new BlurStack();
        if (i === radiusPlus1) {
            stackEnd = stack;
        }
    }
    stack.next = stackStart;
    var stackIn = null;
    var stackOut = null;

    yw = yi = 0;

    var mulSum = mulTable[radius];
    var shgSum;
    for (var ssi = 0; ssi < shgTable.length; ++ssi) {
        if (radius <= shgTable[ssi][0]) {
            shgSum = shgTable[ssi - 1][1];
            break;
        }
    }

    for (y = 0; y < height; y++) {
        rInSum = gInSum = bInSum = rSum = gSum = bSum = 0;

        rOutSum = radiusPlus1 * (pr = pixels[yi]);
        gOutSum = radiusPlus1 * (pg = pixels[yi + 1]);
        bOutSum = radiusPlus1 * (pb = pixels[yi + 2]);

        rSum += sumFactor * pr;
        gSum += sumFactor * pg;
        bSum += sumFactor * pb;

        stack = stackStart;

        for (i = 0; i < radiusPlus1; i++) {
            stack.r = pr;
            stack.g = pg;
            stack.b = pb;
            stack = stack.next;
        }

        for (i = 1; i < radiusPlus1; i++) {
            p = yi + ((width - 1 < i ? width - 1 : i) << 2);
            rSum += (stack.r = (pr = pixels[p])) * (rbs = radiusPlus1 - i);
            gSum += (stack.g = (pg = pixels[p + 1])) * rbs;
            bSum += (stack.b = (pb = pixels[p + 2])) * rbs;

            rInSum += pr;
            gInSum += pg;
            bInSum += pb;

            stack = stack.next;
        }

        stackIn = stackStart;
        stackOut = stackEnd;
        for (x = 0; x < width; x++) {
            pixels[yi] = (rSum * mulSum) >> shgSum;
            pixels[yi + 1] = (gSum * mulSum) >> shgSum;
            pixels[yi + 2] = (bSum * mulSum) >> shgSum;

            rSum -= rOutSum;
            gSum -= gOutSum;
            bSum -= bOutSum;

            rOutSum -= stackIn.r;
            gOutSum -= stackIn.g;
            bOutSum -= stackIn.b;

            p = (yw + ((p = x + radius + 1) < (width - 1) ? p : (width - 1))) << 2;

            rInSum += (stackIn.r = pixels[p]);
            gInSum += (stackIn.g = pixels[p + 1]);
            bInSum += (stackIn.b = pixels[p + 2]);

            rSum += rInSum;
            gSum += gInSum;
            bSum += bInSum;

            stackIn = stackIn.next;

            rOutSum += (pr = stackOut.r);
            gOutSum += (pg = stackOut.g);
            bOutSum += (pb = stackOut.b);

            rInSum -= pr;
            gInSum -= pg;
            bInSum -= pb;

            stackOut = stackOut.next;

            yi += 4;
        }
        yw += width;
    }

    for (x = 0; x < width; x++) {
        gInSum = bInSum = rInSum = gSum = bSum = rSum = 0;

        yi = x << 2;
        rOutSum = radiusPlus1 * (pr = pixels[yi]);
        gOutSum = radiusPlus1 * (pg = pixels[yi + 1]);
        bOutSum = radiusPlus1 * (pb = pixels[yi + 2]);

        rSum += sumFactor * pr;
        gSum += sumFactor * pg;
        bSum += sumFactor * pb;

        stack = stackStart;

        for (i = 0; i < radiusPlus1; i++) {
            stack.r = pr;
            stack.g = pg;
            stack.b = pb;
            stack = stack.next;
        }

        yp = width;

        for (i = 1; i < radiusPlus1; i++) {
            yi = (yp + x) << 2;

            rSum += (stack.r = (pr = pixels[yi])) * (rbs = radiusPlus1 - i);
            gSum += (stack.g = (pg = pixels[yi + 1])) * rbs;
            bSum += (stack.b = (pb = pixels[yi + 2])) * rbs;

            rInSum += pr;
            gInSum += pg;
            bInSum += pb;

            stack = stack.next;

            if (i < (height - 1)) {
                yp += width;
            }
        }

        yi = x;
        stackIn = stackStart;
        stackOut = stackEnd;
        for (y = 0; y < height; y++) {
            p = yi << 2;
            pixels[p] = (rSum * mulSum) >> shgSum;
            pixels[p + 1] = (gSum * mulSum) >> shgSum;
            pixels[p + 2] = (bSum * mulSum) >> shgSum;

            rSum -= rOutSum;
            gSum -= gOutSum;
            bSum -= bOutSum;

            rOutSum -= stackIn.r;
            gOutSum -= stackIn.g;
            bOutSum -= stackIn.b;

            p = (x + (((p = y + radiusPlus1) < (height - 1) ? p : (height - 1)) * width)) << 2;

            rSum += (rInSum += (stackIn.r = pixels[p]));
            gSum += (gInSum += (stackIn.g = pixels[p + 1]));
            bSum += (bInSum += (stackIn.b = pixels[p + 2]));

            stackIn = stackIn.next;

            rOutSum += (pr = stackOut.r);
            gOutSum += (pg = stackOut.g);
            bOutSum += (pb = stackOut.b);

            rInSum -= pr;
            gInSum -= pg;
            bInSum -= pb;

            stackOut = stackOut.next;

            yi += width;
        }
    }

    context.putImageData(imageData, 0, 0);

};

/**
 * Defines a new helper object for Stack Blur Algorithm.
 */
function BlurStack() {
    this.r = 0;
    this.g = 0;
    this.b = 0;
    this.next = null;
}

/**
 * Defines a gravity matrix object which handles collision detection.
 * @param x number of columns in the matrix
 * @param y number of rows in the matrix
 * @param r grid size
 */
function CollisionMatrix(x, y, r) {
    this.resolution = r;
    this.xc = x;
    this.yc = y;
    this.matrix = new Array(x);
    for (var i = 0; i <= (x + 5); i++) {
        this.matrix[i] = new Array(y);
        for (var j = 0; j <= (y + 5); ++j) {
            this.matrix[i][j] = new DropItem(null);
        }
    }
}

/**
 * Updates position of the given drop on the collision matrix.
 * @param drop raindrop to be positioned/repositioned
 * @param forceDelete if true the raindrop will be removed from the matrix
 * @returns collisions if any
 */
CollisionMatrix.prototype.update = function(drop, forceDelete) {
    if (drop.gid) {
        if (!this.matrix[drop.gmx] || !this.matrix[drop.gmx][drop.gmy]) {
            return null;
        }
        this.matrix[drop.gmx][drop.gmy].remove(drop);
        if (forceDelete) {
            return null;
        }

        drop.gmx = Math.floor(drop.x / this.resolution);
        drop.gmy = Math.floor(drop.y / this.resolution);
        if (!this.matrix[drop.gmx] || !this.matrix[drop.gmx][drop.gmy]) {
            return null;
        }
        this.matrix[drop.gmx][drop.gmy].add(drop);

        var collisions = this.collisions(drop);
        if (collisions && collisions.next != null) {
            return collisions.next;
        }
    } else {
        drop.gid = Math.random().toString(36).substr(2, 9);
        drop.gmx = Math.floor(drop.x / this.resolution);
        drop.gmy = Math.floor(drop.y / this.resolution);
        if (!this.matrix[drop.gmx] || !this.matrix[drop.gmx][drop.gmy]) {
            return null;
        }

        this.matrix[drop.gmx][drop.gmy].add(drop);
    }
    return null;
};

/**
 * Looks for collisions with the given raindrop.
 * @param drop raindrop to be checked
 * @returns DropItem list of drops that collide with it
 */
CollisionMatrix.prototype.collisions = function(drop) {
    var item = new DropItem(null);
    var first = item;

    item = this.addAll(item, drop.gmx - 1, drop.gmy + 1);
    item = this.addAll(item, drop.gmx, drop.gmy + 1);
    item = this.addAll(item, drop.gmx + 1, drop.gmy + 1);

    return first;
};

/**
 * Appends all found drop at a given location to the given item.
 * @param to item to which the results will be appended to
 * @param x x position in the matrix
 * @param y y position in the matrix
 * @returns last discovered item on the list
 */
CollisionMatrix.prototype.addAll = function(to, x, y) {
    if (x > 0 && y > 0 && x < this.xc && y < this.yc) {
        var items = this.matrix[x][y];
        while (items.next != null) {
            items = items.next;
            to.next = new DropItem(items.drop);
            to = to.next;
        }
    }
    return to;
};

/**
 * Removed the drop from its current position
 * @param drop to be removed
 */
CollisionMatrix.prototype.remove = function(drop) {
    this.matrix[drop.gmx][drop.gmy].remove(drop);
};

/**
 * Defines a linked list item.
 */
function DropItem(drop) {
    this.drop = drop;
    this.next = null;
}

/**
 * Adds the raindrop to the end of the list.
 * @param drop raindrop to be added
 */
DropItem.prototype.add = function(drop) {
    var item = this;
    while (item.next != null) {
        item = item.next;
    }
    item.next = new DropItem(drop);
};

/**
 * Removes the raindrop from the list.
 * @param drop raindrop to be removed
 */
DropItem.prototype.remove = function(drop) {
    var item = this;
    var prevItem = null;
    while (item.next != null) {
        prevItem = item;
        item = item.next;
        if (item.drop.gid === drop.gid) {
            prevItem.next = item.next;
        }
    }
};