下雪代码特效

最近圣诞节了弄了一个下雪的代码特效，本人觉得还可以就写一个随笔记录一下，方便以后用可以找到。

/** @license
 * DHTML Snowstorm! JavaScript-based snow for web pages
 * Making it snow on the internets since 2003. You're welcome.
 * -----------------------------------------------------------
 * Version 1.44.20131215 (Previous rev: 1.44.20131208)
 * Copyright (c) 2007, Scott Schiller. All rights reserved.
 * Code provided under the BSD License
 * http://schillmania.com/projects/snowstorm/license.txt
 */
var snowStorm = (function(window, document) {

    // --- 基本属性（共性） ---
    this.autoStart = true;          // 雪是否应该自动启动或不启动。
    this.excludeMobile = true;      
    this.flakesMax = 128;           
    this.flakesMaxActive = 100;     
    this.animationInterval = 33;    
    this.useGPU = true;             
    this.className = null;          
    this.excludeMobile = true;      
    this.flakeBottom = null;        
    this.followMouse = false;       
    this.snowColor = '#fff';        
    this.snowCharacter = '';          
    this.snowStick = false;         
    this.targetElement = null;      
    this.useMeltEffect = true;      
    this.useTwinkleEffect = false;  
    this.usePositionFixed = false;  
    this.usePixelPosition = false;  

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

    this.freezeOnBlur = false;      
    this.flakeLeftOffset = 0;      
    this.flakeRightOffset = 0;      
    this.flakeWidth = 50;           
    this.flakeHeight = 50;          
    this.vMaxX = 3;                 
    this.vMaxY = 4;                 
    this.zIndex = 0;                

    // --- "No user-serviceable parts inside" past this point, yadda yadda ---

    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, 2000/(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');
        var startTime = new Date().getMilliseconds();
        var snowImgHtml = '';
        switch(startTime % 13){
            case 0:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_1.png" />';
                break;
            case 1:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow2.png" />';
                break;
            case 2:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_6.png" />';
                break;
            case 3:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_4.png" />';
                break;
            case 4:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow1.png" />';
                break;
            case 5:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_4.png" />';
                break;
            case 6:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow4.png" />';
                break;
            case 7:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow9.png" />';
                break;
            case 8:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_6.png" />';
                break;
            case 9:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_5.png" />';
                break;
            case 10:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow5.png" />';
                break;
            case 11:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow3.png" />';
                break;
            default:
                snowImgHtml = '<img src="http://images.cnblogs.com/cnblogs_com/sunny520/1137300/o_snow1.png" />';
        }
        this.o.innerHTML = snowImgHtml;
        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.top = 'auto';
                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);
            s.vX = 0;
            s.vY = 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));