JS实现图片剪裁并预览效果

今天又疯狂学习了web前端的图片剪裁效果，可以有个区域来框住图片的某一部分，并可以预览框住的部分 

效果图如下：

看着是不是很炫呢

简单介绍下实现方法吧

1.布局就是左右两块div,右边的好说，主要是左边的，左边的用绝对布局的方式分了3层，最下面一层是一个半透明的图片，中间一层是原图，但被剪切成只有一块，也只显示这一块，可以用clip:rect方法实现，然后最上面一层就是自己写的一个边框，在边框上加了8个点，分别给这8个点定义位置。 

2.然后JS代码用了鼠标的点击事件来实现。 

下面贴上自己的代码：

index.html (这里要引用两个js文件，分别是jquery和jquery-ui，其中jquery可以引用网上的，jquery-ui我是自己下在本地引用的，大家可以自己去官网下载，不引用则不能实现拖动剪切框) 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 



 img.css
 

body {
 background-color: #333;
}

#box {
 position: absolute;
 top: 200px;
 left: 100px;
 width: 600px;
 height: 319px;
}

#img1 {
 
 opacity: 0.3;
 position:absolute;
 top: 0;
 left: 0;

}

#img2 {
 position: absolute;
 top: 0;
 left: 0;

 
 clip: rect(0, 200px, 200px, 0);
}

#main {
 position: absolute;
 border: 1px solid #fff;
 width:200px;
 height: 200px;
}

#preview {
 position: absolute;
 width: 600px;
 height: 319px;
 top:200px;
 left: 720px;
}
#preview img{
 
 position: absolute;
}

.minDiv {
 position: absolute;
 width: 8px;
 height: 8px;
 background-color: #fff;
}

.left-up {
 top:-4px;
 left: -4px;

 
 cursor: nw-resize;
}

.up {
 
 left: 50%;
 
 margin-left: -4px;
 top:-4px;
 cursor: n-resize;
}

.right-up {
 right: -4px;
 top: -4px;
 cursor: ne-resize;
}

.right {
 top: 50%;
 margin-top:-4px;
 right: -4px;
 cursor: e-resize;
}

.right-down {
 bottom: -4px;
 right: -4px;
 cursor: se-resize;
}

.down {
 left: 50%;
 margin-left: -4px;
 bottom: -4px;
 cursor: s-resize;
}

.left-down {
 left: -4px;
 bottom: -4px;
 cursor: sw-resize;
}

.left {
 bottom: 50%;
 margin-bottom: -4px;
 left: -4px;
 cursor: w-resize;
}
 img.js
 

// 在元素加载完之后执行，确保元素可以成功获取
window.onload =function(){

 document.onselectstart = new Function('event.returnValue=false;');
 $("#main").draggable({containment:'parent', drag:setChoice});
 var img = document.getElementById("img2");

 var rightDiv = document.getElementById("right");
 var upDiv = document.getElementById("up");
 var leftDiv = document.getElementById("left");
 var downDiv = document.getElementById("down");
 var leftupDiv = document.getElementById("left-up");
 var rightupDiv = document.getElementById("right-up");
 var rightdownDiv = document.getElementById("right-down");
 var leftdownDiv = document.getElementById("left-down");

 var mainDiv = document.getElementById("main");
 var ifKeyDown = false; 

 var contact = "";// 表示被按下的触点

 //鼠标按下状态
 rightDiv.onmousedown = function(e) {
 
 e.stopPropagation();
 ifKeyDown = true;
 contact = "right";
 }
 upDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "up";
 }
 leftDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "left";
 }
 downDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "down";
 }
 leftupDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "left-up";
 }
 rightupDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "right-up";
 }
 rightdownDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "right-down";
 }
 leftdownDiv.onmousedown = function(e) {
 e.stopPropagation();
 ifKeyDown = true;
 contact = "left-down";
 }

 //鼠标松开状态
 window.onmouseup = function() {
 ifKeyDown = false;
 }

 //鼠标移动事件
 window.onmousemove = function(e) {
 if(ifKeyDown == true){

 switch(contact){
 case "right": rightMove(e); break;
 case "up": upMove(e); break;
 case "left": leftMove(e); break;
 case "down": downMove(e); break;
 case "left-up": leftMove(e); upMove(e); break;
 case "right-up": rightMove(e); upMove(e); break;
 case "right-down": rightMove(e); downMove(e); break;
 case "left-down": leftMove(e); downMove(e); break;
 }

 }
 setChoice();
 setPreview();
 
 }
 //右边移动
 function rightMove(e) {
 var x = e.clientX; //鼠标x坐标
 var addWidth = ""; //鼠标移动后选取框增加的宽度
 var widthBefore = mainDiv.offsetWidth - 2; //选取框变化前的宽度，减2是为了减去边框border的宽，左右两边各为1px，所以是2
 addWidth = x - getPosition(mainDiv).left //鼠标移动后增加的宽度
 if(widthBefore <= img.width){
 mainDiv.style.width = addWidth + "px"; //选取框变化后的宽度
 } else {
 mainDiv.style.width = img.width + "px";
 }
 }

 //上边移动
 function upMove(e) {
 var topBefore = mainDiv.offsetTop;
 var y = e.clientY;//鼠标纵坐标
 var addHeight = 0;
 var mainY = getPosition(mainDiv).top;//选取框相对于屏幕上边的距离
 addHeight = y - mainY; //增加的高度
 var heightBefore = mainDiv.offsetHeight - 2;
 var bottom = topBefore + heightBefore;

 var heightAfter = heightBefore - addHeight;
 var topAfter = mainDiv.offsetTop + addHeight;

 if(topAfter < bottom && topAfter > -2){
 mainDiv.style.height = heightAfter + "px";
 mainDiv.style.top = topAfter + "px";
 }

 }

 //左边移动
 function leftMove(e) {
 // 左边框变化前距离父元素左边的距离
 var leftBefore = mainDiv.offsetLeft;
 // 鼠标按下停止后鼠标距离浏览器左边界的距离
 var x = e.clientX;
 // 定义增加的宽度
 var addWidth = 0;
 // 变化之前剪辑框的宽度
 var widthBefore = mainDiv.offsetWidth - 2;
 // 变化之前左边框距离浏览器左边界的距离
 var mainDivLeft = getPosition(mainDiv).left;
 // 右边框距离父元素的左边的距离
 var right = leftBefore + widthBefore;
 // 增加的宽度
 addWidth = x - mainDivLeft;
 // 变化之后剪辑框的宽度
 var widthAfter = widthBefore - addWidth;
 // 变化之后剪辑框离左边的距离
 var leftAfter = mainDiv.offsetLeft + addWidth;
 // 防止左边框移到右边框以外区域
 if(leftAfter < right && leftAfter > -2) {
 // 定义变化后的宽度
 mainDiv.style.width = widthAfter + "px";
 // 定义变化后距离左边父元素的距离
 mainDiv.style.left = leftAfter + "px";
 }
 
 }

 //下边移动
 function downMove(e) {
 var y = e.clientY;
 var addHeight = 0;
 var heightBefore = mainDiv.offsetHeight - 2;
 addHeight = y - getPosition(mainDiv).top;
 if(heightBefore <= img.height) {
 mainDiv.style.height = addHeight + "px";
 } else {
 mainDiv.style.height = img.height + "px";
 }
 
 }


 // 获取元素相对于屏幕左边的距离，利用offsetLeft
 // node为传入的元素
 function getPosition(node) {
 
 var left = node.offsetLeft;
 
 var top = node.offsetTop;
 
 var parent = node.offsetParent;
 
 while(parent != null) {
 
 left += parent.offsetLeft;
 
 top += parent.offsetTop;
 
 parent = parent.offsetParent;
 }
 return {"left":left,"top":top};
 }


 //设置选取区域高亮可见
 function setChoice() {
 var top = mainDiv.offsetTop;
 var right = mainDiv.offsetLeft + mainDiv.offsetWidth;
 var bottom = mainDiv.offsetTop + mainDiv.offsetHeight;
 var left = mainDiv.offsetLeft;
 img.style.clip = "rect("+ top+"px,"+ right+"px,"+ bottom +"px,"+ left+"px"+")"
 }

 //预览函数
 function setPreview() {
 var top = mainDiv.offsetTop;
 var right = mainDiv.offsetLeft + mainDiv.offsetWidth;
 var bottom = mainDiv.offsetTop + mainDiv.offsetHeight;
 var left = mainDiv.offsetLeft;
 var img3 = document.getElementById("img3");
 img3.style.clip = "rect("+ top+"px,"+ right+"px,"+ bottom +"px,"+ left+"px"+")"
 
 img3.style.top = -(top) + "px";
 img3.style.left = -(left) + "px";
 }
}

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