snowstorm.js

/** @license
 * DHTML Snowstorm! JavaScript-based snow for web pages
 * Making it snow on the internets since 2003. You're welcome.
 * -----------------------------------------------------------
 * Version 1.44.20131208 (Previous rev: 1.44.20131125)
 * Copyright (c) 2007, Scott Schiller. All rights reserved.
 * Code provided under the BSD License
 * http://schillmania.com/projects/snowstorm/license.txt
 */

/*jslint nomen: true, plusplus: true, sloppy: true, vars: true, white: true */
/*global window, document, navigator, clearInterval, setInterval */

var snowStorm = (function (window, document) {

    // --- common properties ---

    this.autoStart = true;          // Whether the snow should start automatically or not.
    this.excludeMobile = true;      // Snow is likely to be bad news for mobile phones' CPUs (and batteries.) Enable at your own risk.
    this.flakesMax = 128;           // Limit total amount of snow made (falling + sticking)
    this.flakesMaxActive = 64;      // Limit amount of snow falling at once (less = lower CPU use)
    this.animationInterval = 33;    // Theoretical "miliseconds per frame" measurement. 20 = fast + smooth, but high CPU use. 50 = more conservative, but slower
    this.useGPU = true;             // Enable transform-based hardware acceleration, reduce CPU load.
    this.className = null;          // CSS class name for further customization on snow elements
    this.excludeMobile = true;      // Snow is likely to be bad news for mobile phones' CPUs (and batteries.) By default, be nice.
    this.flakeBottom = null;        // Integer for Y axis snow limit, 0 or null for "full-screen" snow effect
    this.followMouse = true;        // Snow movement can respond to the user's mouse
    this.snowColor = '#fff';        // Don't eat (or use?) yellow snow.
    this.snowCharacter = '•';  // • = bullet, · is square on some systems etc.
    this.snowStick = true;          // Whether or not snow should "stick" at the bottom. When off, will never collect.
    this.targetElement = null;      // element which snow will be appended to (null = document.body) - can be an element ID eg. 'myDiv', or a DOM node reference
    this.useMeltEffect = true;      // When recycling fallen snow (or rarely, when falling), have it "melt" and fade out if browser supports it
    this.useTwinkleEffect = false;  // Allow snow to randomly "flicker" in and out of view while falling
    this.usePositionFixed = false;  // true = snow does not shift vertically when scrolling. May increase CPU load, disabled by default - if enabled, used only where supported
    this.usePixelPosition = false;  // Whether to use pixel values for snow top/left vs. percentages. Auto-enabled if body is position:relative or targetElement is specified.

    // --- less-used bits ---

    this.freezeOnBlur = true;       // Only snow when the window is in focus (foreground.) Saves CPU.
    this.flakeLeftOffset = 0;       // Left margin/gutter space on edge of container (eg. browser window.) Bump up these values if seeing horizontal scrollbars.
    this.flakeRightOffset = 0;      // Right margin/gutter space on edge of container
    this.flakeWidth = 8;            // Max pixel width reserved for snow element
    this.flakeHeight = 8;           // Max pixel height reserved for snow element
    this.vMaxX = 5;                 // Maximum X velocity range for snow
    this.vMaxY = 4;                 // Maximum Y velocity range for snow
    this.zIndex = 0;                // CSS stacking order applied to each snowflake

    // --- "No user-serviceable parts inside" past this point.---

    var storm = this,
        features,
        // UA sniffing and backCompat rendering mode checks for fixed position, etc.
        isIE = navigator.userAgent.match(/msie/i),
        isIE6 = navigator.userAgent.match(/msie 6/i),
        isMobile = navigator.userAgent.match(/mobile|opera m(ob|in)/i),
        isBackCompatIE = (isIE && document.compatMode === 'BackCompat'),
        noFixed = (isBackCompatIE || isIE6),
        screenX = null, screenX2 = null, screenY = null, scrollY = null, docHeight = null, vRndX = null, vRndY = null,
        windOffset = 1,
        windMultiplier = 2,
        flakeTypes = 6,
        fixedForEverything = false,
        targetElementIsRelative = false,
        opacitySupported = (function () {
            try {
                document.createElement('div').style.opacity = '0.5';
            } catch (e) {
                return false;
            }
            return true;
        }()),
        didInit = false,
        docFrag = document.createDocumentFragment();

    features = (function () {

        var getAnimationFrame;

        /**
         * hat tip: paul irish
         * http://paulirish.com/2011/requestanimationframe-for-smart-animating/
         * https://gist.github.com/838785
         */

        function timeoutShim(callback) {
            window.setTimeout(callback, 1000 / (storm.animationInterval || 20));
        }

        var _animationFrame = (window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            window.mozRequestAnimationFrame ||
            window.oRequestAnimationFrame ||
            window.msRequestAnimationFrame ||
            timeoutShim);

        // apply to window, avoid "illegal invocation" errors in Chrome
        getAnimationFrame = _animationFrame ? function () {
            return _animationFrame.apply(window, arguments);
        } : null;

        var testDiv;

        testDiv = document.createElement('div');

        function has(prop) {

            // test for feature support
            var result = testDiv.style[prop];
            return (result !== undefined ? prop : null);

        }

        // note local scope.
        var localFeatures = {

            transform: {
                ie: has('-ms-transform'),
                moz: has('MozTransform'),
                opera: has('OTransform'),
                webkit: has('webkitTransform'),
                w3: has('transform'),
                prop: null // the normalized property value
            },

            getAnimationFrame: getAnimationFrame

        };

        localFeatures.transform.prop = (
            localFeatures.transform.w3 ||
            localFeatures.transform.moz ||
            localFeatures.transform.webkit ||
            localFeatures.transform.ie ||
            localFeatures.transform.opera
        );

        testDiv = null;

        return localFeatures;

    }());

    this.timer = null;
    this.flakes = [];
    this.disabled = false;
    this.active = false;
    this.meltFrameCount = 20;
    this.meltFrames = [];

    this.setXY = function (o, x, y) {

        if (!o) {
            return false;
        }

        if (storm.usePixelPosition || targetElementIsRelative) {

            o.style.left = (x - storm.flakeWidth) + 'px';
            o.style.top = (y - storm.flakeHeight) + 'px';

        } else if (noFixed) {

            o.style.right = (100 - (x / screenX * 100)) + '%';
            // avoid creating vertical scrollbars
            o.style.top = (Math.min(y, docHeight - storm.flakeHeight)) + 'px';

        } else {

            if (!storm.flakeBottom) {

                // if not using a fixed bottom coordinate...
                o.style.right = (100 - (x / screenX * 100)) + '%';
                o.style.bottom = (100 - (y / screenY * 100)) + '%';

            } else {

                // absolute top.
                o.style.right = (100 - (x / screenX * 100)) + '%';
                o.style.top = (Math.min(y, docHeight - storm.flakeHeight)) + 'px';

            }

        }

    };

    this.events = (function () {

        var old = (!window.addEventListener && window.attachEvent), slice = Array.prototype.slice,
            evt = {
                add: (old ? 'attachEvent' : 'addEventListener'),
                remove: (old ? 'detachEvent' : 'removeEventListener')
            };

        function getArgs(oArgs) {
            var args = slice.call(oArgs), len = args.length;
            if (old) {
                args[1] = 'on' + args[1]; // prefix
                if (len > 3) {
                    args.pop(); // no capture
                }
            } else if (len === 3) {
                args.push(false);
            }
            return args;
        }

        function apply(args, sType) {
            var element = args.shift(),
                method = [evt[sType]];
            if (old) {
                element[method](args[0], args[1]);
            } else {
                element[method].apply(element, args);
            }
        }

        function addEvent() {
            apply(getArgs(arguments), 'add');
        }

        function removeEvent() {
            apply(getArgs(arguments), 'remove');
        }

        return {
            add: addEvent,
            remove: removeEvent
        };

    }());

    function rnd(n, min) {
        if (isNaN(min)) {
            min = 0;
        }
        return (Math.random() * n) + min;
    }

    function plusMinus(n) {
        return (parseInt(rnd(2), 10) === 1 ? n * -1 : n);
    }

    this.randomizeWind = function () {
        var i;
        vRndX = plusMinus(rnd(storm.vMaxX, 0.2));
        vRndY = rnd(storm.vMaxY, 0.2);
        if (this.flakes) {
            for (i = 0; i < this.flakes.length; i++) {
                if (this.flakes[i].active) {
                    this.flakes[i].setVelocities();
                }
            }
        }
    };

    this.scrollHandler = function () {
        var i;
        // "attach" snowflakes to bottom of window if no absolute bottom value was given
        scrollY = (storm.flakeBottom ? 0 : parseInt(window.scrollY || document.documentElement.scrollTop || (noFixed ? document.body.scrollTop : 0), 10));
        if (isNaN(scrollY)) {
            scrollY = 0; // Netscape 6 scroll fix
        }
        if (!fixedForEverything && !storm.flakeBottom && storm.flakes) {
            for (i = 0; i < storm.flakes.length; i++) {
                if (storm.flakes[i].active === 0) {
                    storm.flakes[i].stick();
                }
            }
        }
    };

    this.resizeHandler = function () {
        if (window.innerWidth || window.innerHeight) {
            screenX = window.innerWidth - 16 - storm.flakeRightOffset;
            screenY = (storm.flakeBottom || window.innerHeight);
        } else {
            screenX = (document.documentElement.clientWidth || document.body.clientWidth || document.body.scrollWidth) - (!isIE ? 8 : 0) - storm.flakeRightOffset;
            screenY = storm.flakeBottom || document.documentElement.clientHeight || document.body.clientHeight || document.body.scrollHeight;
        }
        docHeight = document.body.offsetHeight;
        screenX2 = parseInt(screenX / 2, 10);
    };

    this.resizeHandlerAlt = function () {
        screenX = storm.targetElement.offsetWidth - storm.flakeRightOffset;
        screenY = storm.flakeBottom || storm.targetElement.offsetHeight;
        screenX2 = parseInt(screenX / 2, 10);
        docHeight = document.body.offsetHeight;
    };

    this.freeze = function () {
        // pause animation
        if (!storm.disabled) {
            storm.disabled = 1;
        } else {
            return false;
        }
        storm.timer = null;
    };

    this.resume = function () {
        if (storm.disabled) {
            storm.disabled = 0;
        } else {
            return false;
        }
        storm.timerInit();
    };

    this.toggleSnow = function () {
        if (!storm.flakes.length) {
            // first run
            storm.start();
        } else {
            storm.active = !storm.active;
            if (storm.active) {
                storm.show();
                storm.resume();
            } else {
                storm.stop();
                storm.freeze();
            }
        }
    };

    this.stop = function () {
        var i;
        this.freeze();
        for (i = 0; i < this.flakes.length; i++) {
            this.flakes[i].o.style.display = 'none';
        }
        storm.events.remove(window, 'scroll', storm.scrollHandler);
        storm.events.remove(window, 'resize', storm.resizeHandler);
        if (storm.freezeOnBlur) {
            if (isIE) {
                storm.events.remove(document, 'focusout', storm.freeze);
                storm.events.remove(document, 'focusin', storm.resume);
            } else {
                storm.events.remove(window, 'blur', storm.freeze);
                storm.events.remove(window, 'focus', storm.resume);
            }
        }
    };

    this.show = function () {
        var i;
        for (i = 0; i < this.flakes.length; i++) {
            this.flakes[i].o.style.display = 'block';
        }
    };

    this.SnowFlake = function (type, x, y) {
        var s = this;
        this.type = type;
        this.x = x || parseInt(rnd(screenX - 20), 10);
        this.y = (!isNaN(y) ? y : -rnd(screenY) - 12);
        this.vX = null;
        this.vY = null;
        this.vAmpTypes = [1, 1.2, 1.4, 1.6, 1.8]; // "amplification" for vX/vY (based on flake size/type)
        this.vAmp = this.vAmpTypes[this.type] || 1;
        this.melting = false;
        this.meltFrameCount = storm.meltFrameCount;
        this.meltFrames = storm.meltFrames;
        this.meltFrame = 0;
        this.twinkleFrame = 0;
        this.active = 1;
        this.fontSize = (10 + (this.type / 5) * 10);
        this.o = document.createElement('div');
        this.o.innerHTML = storm.snowCharacter;
        if (storm.className) {
            this.o.setAttribute('class', storm.className);
        }
        this.o.style.color = storm.snowColor;
        this.o.style.position = (fixedForEverything ? 'fixed' : 'absolute');
        if (storm.useGPU && features.transform.prop) {
            // GPU-accelerated snow.
            this.o.style[features.transform.prop] = 'translate3d(0px, 0px, 0px)';
        }
        this.o.style.width = storm.flakeWidth + 'px';
        this.o.style.height = storm.flakeHeight + 'px';
        this.o.style.fontFamily = 'arial,verdana';
        this.o.style.cursor = 'default';
        this.o.style.overflow = 'hidden';
        this.o.style.fontWeight = 'normal';
        this.o.style.zIndex = storm.zIndex;
        docFrag.appendChild(this.o);

        this.refresh = function () {
            if (isNaN(s.x) || isNaN(s.y)) {
                // safety check
                return false;
            }
            storm.setXY(s.o, s.x, s.y);
        };

        this.stick = function () {
            if (noFixed || (storm.targetElement !== document.documentElement && storm.targetElement !== document.body)) {
                s.o.style.top = (screenY + scrollY - storm.flakeHeight) + 'px';
            } else if (storm.flakeBottom) {
                s.o.style.top = storm.flakeBottom + 'px';
            } else {
                s.o.style.display = 'none';
                s.o.style.bottom = '0%';
                s.o.style.position = 'fixed';
                s.o.style.display = 'block';
            }
        };

        this.vCheck = function () {
            if (s.vX >= 0 && s.vX < 0.2) {
                s.vX = 0.2;
            } else if (s.vX < 0 && s.vX > -0.2) {
                s.vX = -0.2;
            }
            if (s.vY >= 0 && s.vY < 0.2) {
                s.vY = 0.2;
            }
        };

        this.move = function () {
            var vX = s.vX * windOffset, yDiff;
            s.x += vX;
            s.y += (s.vY * s.vAmp);
            if (s.x >= screenX || screenX - s.x < storm.flakeWidth) { // X-axis scroll check
                s.x = 0;
            } else if (vX < 0 && s.x - storm.flakeLeftOffset < -storm.flakeWidth) {
                s.x = screenX - storm.flakeWidth - 1; // flakeWidth;
            }
            s.refresh();
            yDiff = screenY + scrollY - s.y + storm.flakeHeight;
            if (yDiff < storm.flakeHeight) {
                s.active = 0;
                if (storm.snowStick) {
                    s.stick();
                } else {
                    s.recycle();
                }
            } else {
                if (storm.useMeltEffect && s.active && s.type < 3 && !s.melting && Math.random() > 0.998) {
                    // ~1/1000 chance of melting mid-air, with each frame
                    s.melting = true;
                    s.melt();
                    // only incrementally melt one frame
                    // s.melting = false;
                }
                if (storm.useTwinkleEffect) {
                    if (s.twinkleFrame < 0) {
                        if (Math.random() > 0.97) {
                            s.twinkleFrame = parseInt(Math.random() * 8, 10);
                        }
                    } else {
                        s.twinkleFrame--;
                        if (!opacitySupported) {
                            s.o.style.visibility = (s.twinkleFrame && s.twinkleFrame % 2 === 0 ? 'hidden' : 'visible');
                        } else {
                            s.o.style.opacity = (s.twinkleFrame && s.twinkleFrame % 2 === 0 ? 0 : 1);
                        }
                    }
                }
            }
        };

        this.animate = function () {
            // main animation loop
            // move, check status, die etc.
            s.move();
        };

        this.setVelocities = function () {
            s.vX = vRndX + rnd(storm.vMaxX * 0.12, 0.1);
            s.vY = vRndY + rnd(storm.vMaxY * 0.12, 0.1);
        };

        this.setOpacity = function (o, opacity) {
            if (!opacitySupported) {
                return false;
            }
            o.style.opacity = opacity;
        };

        this.melt = function () {
            if (!storm.useMeltEffect || !s.melting) {
                s.recycle();
            } else {
                if (s.meltFrame < s.meltFrameCount) {
                    s.setOpacity(s.o, s.meltFrames[s.meltFrame]);
                    s.o.style.fontSize = s.fontSize - (s.fontSize * (s.meltFrame / s.meltFrameCount)) + 'px';
                    s.o.style.lineHeight = storm.flakeHeight + 2 + (storm.flakeHeight * 0.75 * (s.meltFrame / s.meltFrameCount)) + 'px';
                    s.meltFrame++;
                } else {
                    s.recycle();
                }
            }
        };

        this.recycle = function () {
            s.o.style.display = 'none';
            s.o.style.position = (fixedForEverything ? 'fixed' : 'absolute');
            s.o.style.bottom = 'auto';
            s.setVelocities();
            s.vCheck();
            s.meltFrame = 0;
            s.melting = false;
            s.setOpacity(s.o, 1);
            s.o.style.padding = '0px';
            s.o.style.margin = '0px';
            s.o.style.fontSize = s.fontSize + 'px';
            s.o.style.lineHeight = (storm.flakeHeight + 2) + 'px';
            s.o.style.textAlign = 'center';
            s.o.style.verticalAlign = 'baseline';
            s.x = parseInt(rnd(screenX - storm.flakeWidth - 20), 10);
            s.y = parseInt(rnd(screenY) * -1, 10) - storm.flakeHeight;
            s.refresh();
            s.o.style.display = 'block';
            s.active = 1;
        };

        this.recycle(); // set up x/y coords etc.
        this.refresh();

    };

    this.snow = function () {
        var active = 0, flake = null, i, j;
        for (i = 0, j = storm.flakes.length; i < j; i++) {
            if (storm.flakes[i].active === 1) {
                storm.flakes[i].move();
                active++;
            }
            if (storm.flakes[i].melting) {
                storm.flakes[i].melt();
            }
        }
        if (active < storm.flakesMaxActive) {
            flake = storm.flakes[parseInt(rnd(storm.flakes.length), 10)];
            if (flake.active === 0) {
                flake.melting = true;
            }
        }
        if (storm.timer) {
            features.getAnimationFrame(storm.snow);
        }
    };

    this.mouseMove = function (e) {
        if (!storm.followMouse) {
            return true;
        }
        var x = parseInt(e.clientX, 10);
        if (x < screenX2) {
            windOffset = -windMultiplier + (x / screenX2 * windMultiplier);
        } else {
            x -= screenX2;
            windOffset = (x / screenX2) * windMultiplier;
        }
    };

    this.createSnow = function (limit, allowInactive) {
        var i;
        for (i = 0; i < limit; i++) {
            storm.flakes[storm.flakes.length] = new storm.SnowFlake(parseInt(rnd(flakeTypes), 10));
            if (allowInactive || i > storm.flakesMaxActive) {
                storm.flakes[storm.flakes.length - 1].active = -1;
            }
        }
        storm.targetElement.appendChild(docFrag);
    };

    this.timerInit = function () {
        storm.timer = true;
        storm.snow();
    };

    this.init = function () {
        var i;
        for (i = 0; i < storm.meltFrameCount; i++) {
            storm.meltFrames.push(1 - (i / storm.meltFrameCount));
        }
        storm.randomizeWind();
        storm.createSnow(storm.flakesMax); // create initial batch
        storm.events.add(window, 'resize', storm.resizeHandler);
        storm.events.add(window, 'scroll', storm.scrollHandler);
        if (storm.freezeOnBlur) {
            if (isIE) {
                storm.events.add(document, 'focusout', storm.freeze);
                storm.events.add(document, 'focusin', storm.resume);
            } else {
                storm.events.add(window, 'blur', storm.freeze);
                storm.events.add(window, 'focus', storm.resume);
            }
        }
        storm.resizeHandler();
        storm.scrollHandler();
        if (storm.followMouse) {
            storm.events.add(isIE ? document : window, 'mousemove', storm.mouseMove);
        }
        storm.animationInterval = Math.max(20, storm.animationInterval);
        storm.timerInit();
    };

    this.start = function (bFromOnLoad) {
        if (!didInit) {
            didInit = true;
        } else if (bFromOnLoad) {
            // already loaded and running
            return true;
        }
        if (typeof storm.targetElement === 'string') {
            var targetID = storm.targetElement;
            storm.targetElement = document.getElementById(targetID);
            if (!storm.targetElement) {
                throw new Error('Snowstorm: Unable to get targetElement "' + targetID + '"');
            }
        }
        if (!storm.targetElement) {
            storm.targetElement = (document.body || document.documentElement);
        }
        if (storm.targetElement !== document.documentElement && storm.targetElement !== document.body) {
            // re-map handler to get element instead of screen dimensions
            storm.resizeHandler = storm.resizeHandlerAlt;
            //and force-enable pixel positioning
            storm.usePixelPosition = true;
        }
        storm.resizeHandler(); // get bounding box elements
        storm.usePositionFixed = (storm.usePositionFixed && !noFixed && !storm.flakeBottom); // whether or not position:fixed is to be used
        if (window.getComputedStyle) {
            // attempt to determine if body or user-specified snow parent element is relatlively-positioned.
            try {
                targetElementIsRelative = (window.getComputedStyle(storm.targetElement, null).getPropertyValue('position') === 'relative');
            } catch (e) {
                // oh well
                targetElementIsRelative = false;
            }
        }
        fixedForEverything = storm.usePositionFixed;
        if (screenX && screenY && !storm.disabled) {
            storm.init();
            storm.active = true;
        }
    };

    function doDelayedStart() {
        window.setTimeout(function () {
            storm.start(true);
        }, 20);
        // event cleanup
        storm.events.remove(isIE ? document : window, 'mousemove', doDelayedStart);
    }

    function doStart() {
        if (!storm.excludeMobile || !isMobile) {
            doDelayedStart();
        }
        // event cleanup
        storm.events.remove(window, 'load', doStart);
    }

    // hooks for starting the snow
    if (storm.autoStart) {
        storm.events.add(window, 'load', doStart, false);
    }

    return this;

}(window, document));