制作图片倾斜（tilt）效果

摘要：上面这段结构经过脚本处理之后，会被替换成下面的结构脚本分析我们利用了这个插件对上面的图片进行处理，来实现倾斜效果。

原文来自：

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http://tympanus.net/codrops/2015/05/28/image-tilt-effect/

所谓的倾斜效果，我也不知如何用语言描述，那就直接看Demo啦，下面我们会对这个效果的实现原理逐步分析：
http://codepen.io/CodingMonkeyzh/pen/jPYNyr

对一个图片添加该效果，首先，我们需要一个具有宽高的容器。DOM 结构非常简单。

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上面这段结构经过脚本处理之后，会被替换成下面的结构：

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我们利用了filtfx.js这个插件对上面的图片进行处理， 来实现倾斜效果。我在原来的代码中加入了一些注释，来帮助我们理解。下面我们对该插件的核心代码进行分析。

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function TiltFx(el, options) {
  this.el = el;
  this.options = extend({}, this.options);
  extend(this.options, options);
  this._init();
  this._initEvents();
}

这是构造函数，如果我们的文档中，加入了上面的插件，那么插件会遍历文档中具有tilt-effet的img元素，来调用构造函数TiltFx()：

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function init() {
  // 遍历所有拥有‘title-effect’类的img元素
  [].slice.call(document.querySelectorAll("img.tilt-effect")).forEach(function(img) {
    new TiltFx(img, JSON.parse(img.getAttribute("data-tilt-options")));
  });
}

TiltFx()具有一个原型属性，两个原型方法。原型属性配置了一些默认的参数用于调用：

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/**
 * 默认参数
 */
TiltFx.prototype.options = {
  extraImgs: 2, // 额外的辅助图片数量
  opacity: 0.7,
  bgfixed: true, // 底图是否固定
  movement: {    // 这是一些用于移动的参数
    perspective: 1000,
    translateX: -10,
    translateY: -10, 
    translateZ: 20,
    rotateX: 2,
    rotateY: 2,
    rotateZ: 0
  }
}

第一个原型方法是_init()，用于初始化DOM结点，生成我们的目标DOM结点：

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TiltFx.prototype._init = function() {
  this.tiltWrapper = document.createElement("div");
  this.tiltWrapper.className = "tilt";
  // main image element.
  this.tiltImgBack = document.createElement("div");
  this.tiltImgBack.className = "tilt__back";
  this.tiltImgBack.style.backgroundImage = "url(" + this.el.src + ")";
  this.tiltWrapper.appendChild(this.tiltImgBack);
  // image elements limit.
  if (this.options.extraImgs < 1) {
    this.options.extraImgs = 1;
  } else if (this.options.extraImgs > 5) {
    this.options.extraImgs = 5;
  }
  if (!this.options.movement.perspective) {
    this.options.movement.perspective = 0;
  }
  // add the extra image elements.
  this.imgElems = [];
  for (var i = 0; i < this.options.extraImgs; ++i) {
    var el = document.createElement("div");
    el.className = "tilt__front";
    el.style.backgroundImage = "url(" + this.el.src + ")";
    el.style.opacity = this.options.opacity;
    this.tiltWrapper.appendChild(el);
    this.imgElems.push(el);
  }
  if (!this.options.bgfixed) {
    this.imgElems.push(this.tiltImgBack);
    ++this.options.extraImgs;
  }
  // add it to the DOM and remove original img element.
  this.el.parentNode.insertBefore(this.tiltWrapper, this.el);
  this.el.parentNode.removeChild(this.el);
  // tiltWrapper properties: width/height/left/top
  this.view = {
    width: this.tiltWrapper.offsetWidth,
    height: this.tiltWrapper.offsetHeight
  };
};

另外一个原型方式是用于监听鼠标事件之类的：

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TiltFx.prototype._initEvents = function() {
  var self = this,
    moveOpts = self.options.movement;
  // mousemove event..
  this.tiltWrapper.addEventListener("mousemove", function(ev) {
    requestAnimationFrame(function() {
      // mouse position relative to the document.
      var mousepos = getMousePos(ev),
        // document scrolls.
        docScrolls = {
          left: document.body.scrollLeft + document.documentElement.scrollLeft,
          top: document.body.scrollTop + document.documentElement.scrollTop
        },
        bounds = self.tiltWrapper.getBoundingClientRect(),
        // mouse position relative to the main element (tiltWrapper).
        relmousepos = {
          x: mousepos.x - bounds.left - docScrolls.left,
          y: mousepos.y - bounds.top - docScrolls.top
        };
      // configure the movement for each image element.
      for (var i = 0, len = self.imgElems.length; i < len; ++i) {
        var el = self.imgElems[i],
          rotX = moveOpts.rotateX ? 2 * ((i + 1) * moveOpts.rotateX / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.rotateX / self.options.extraImgs) : 0,
          rotY = moveOpts.rotateY ? 2 * ((i + 1) * moveOpts.rotateY / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.rotateY / self.options.extraImgs) : 0,
          rotZ = moveOpts.rotateZ ? 2 * ((i + 1) * moveOpts.rotateZ / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.rotateZ / self.options.extraImgs) : 0,
          transX = moveOpts.translateX ? 2 * ((i + 1) * moveOpts.translateX / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.translateX / self.options.extraImgs) : 0,
          transY = moveOpts.translateY ? 2 * ((i + 1) * moveOpts.translateY / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.translateY / self.options.extraImgs) : 0,
          transZ = moveOpts.translateZ ? 2 * ((i + 1) * moveOpts.translateZ / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.translateZ / self.options.extraImgs) : 0;
        el.style.WebkitTransform = "perspective(" + moveOpts.perspective + "px) translate3d(" + transX + "px," + transY + "px," + transZ + "px) rotate3d(1,0,0," + rotX + "deg) rotate3d(0,1,0," + rotY + "deg) rotate3d(0,0,1," + rotZ + "deg)";
        el.style.transform = "perspective(" + moveOpts.perspective + "px) translate3d(" + transX + "px," + transY + "px," + transZ + "px) rotate3d(1,0,0," + rotX + "deg) rotate3d(0,1,0," + rotY + "deg) rotate3d(0,0,1," + rotZ + "deg)";
      }
    });
  });
  // reset all when mouse leaves the main wrapper.
  this.tiltWrapper.addEventListener("mouseleave", function(ev) {
    setTimeout(function() {
      for (var i = 0, len = self.imgElems.length; i < len; ++i) {
        var el = self.imgElems[i];
        el.style.WebkitTransform = "perspective(" + moveOpts.perspective + "px) translate3d(0,0,0) rotate3d(1,1,1,0deg)";
        el.style.transform = "perspective(" + moveOpts.perspective + "px) translate3d(0,0,0) rotate3d(1,1,1,0deg)";
      }
    }, 60);
  });
  // window resize
  window.addEventListener("resize", throttle(function(ev) {
    // recalculate tiltWrapper properties: width/height/left/top
    self.view = {
      width: self.tiltWrapper.offsetWidth,
      height: self.tiltWrapper.offsetHeight
    };
  }, 50));
};

我们可以看到，监听mousemove的事件处理函数中的计算比较复杂，关键的部分就是在这里：

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        var el = self.imgElems[i],
          rotX = moveOpts.rotateX ? 2 * ((i + 1) * moveOpts.rotateX / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.rotateX / self.options.extraImgs) : 0,
          rotY = moveOpts.rotateY ? 2 * ((i + 1) * moveOpts.rotateY / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.rotateY / self.options.extraImgs) : 0,
          rotZ = moveOpts.rotateZ ? 2 * ((i + 1) * moveOpts.rotateZ / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.rotateZ / self.options.extraImgs) : 0,
          transX = moveOpts.translateX ? 2 * ((i + 1) * moveOpts.translateX / self.options.extraImgs) / self.view.width * relmousepos.x - ((i + 1) * moveOpts.translateX / self.options.extraImgs) : 0,
          transY = moveOpts.translateY ? 2 * ((i + 1) * moveOpts.translateY / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.translateY / self.options.extraImgs) : 0,
          transZ = moveOpts.translateZ ? 2 * ((i + 1) * moveOpts.translateZ / self.options.extraImgs) / self.view.height * relmousepos.y - ((i + 1) * moveOpts.translateZ / self.options.extraImgs) : 0;
        el.style.WebkitTransform = "perspective(" + moveOpts.perspective + "px) translate3d(" + transX + "px," + transY + "px," + transZ + "px) rotate3d(1,0,0," + rotX + "deg) rotate3d(0,1,0," + rotY + "deg) rotate3d(0,0,1," + rotZ + "deg)";
        el.style.transform = "perspective(" + moveOpts.perspective + "px) translate3d(" + transX + "px," + transY + "px," + transZ + "px) rotate3d(1,0,0," + rotX + "deg) rotate3d(0,1,0," + rotY + "deg) rotate3d(0,0,1," + rotZ + "deg)";

这里我们根据鼠标的位置，计算出了各个图层对应的偏移量和旋转角度，然后对它们进行变换即可。
最后mouseleave之后，我们再把个个图层恢复到初始位置就行了。

Demo：http://codepen.io/CodingMonkeyzh/pen/jPYNyr