js原生碰撞检测

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
div{100px;
    height:100px;
}
#box{background:red; position:absolute; }
#box1{background:green;position:absolute;top:300px; left:300px;}
</style>
<script>
//两个碰撞的盒子。是建立在一个不动的基础上。所以可以根据不动的盒子求出四个方向的left和top值。然后再判断其是否碰撞，且碰撞的过程随时改变其层级，（原需 var 8个变量，现在只需4个变量）
function collText(obj,left,top,obj1){
            var l1=obj.offsetLeft-obj.offsetWidth;
            var t1=obj.offsetTop-obj.offsetHeight;
            var r1=obj.offsetLeft+obj.offsetWidth;
            var b1=obj.offsetTop+obj.offsetHeight;
            if(left<l1||top<t1||left>r1||top>b1){
                obj.style.zIndex=3;
                obj1.style.zIndex=1;
                return true;    
            }else{
                obj.style.zIndex=1;
                obj1.style.zIndex=3;
                return false;
            }
};
window.onload=function(){
    var oBox=document.getElementById('box');    
    var oBox1=document.getElementById('box1');
    oBox.onmousedown=function(ev){
        var oEvent= ev   ||    event;
        var disX=oEvent.clientX-oBox.offsetLeft;
        var disY=oEvent.clientY-oBox.offsetTop;
        document.onmousemove=function(ev){
            var oEvent= ev  ||    event;
            var l=oEvent.clientX-disX;
            var t=oEvent.clientY-disY;
            oBox.style.left=l+'px'    ;
            oBox.style.top=t+'px'    ;
            if(collText(oBox1,l,t,oBox)){
                oBox1.style.background='green';
            }else{
                oBox1.style.background='yellow';        
            }
            
        };
        document.onmouseup=function(){
            document.onmousemove=null;    
            document.onmouseup=null;
            oBox.reseaseCapture&&oBox.reseaseCapture();
        };
        oBox.setCapture&&oBox.setCapture();
        return false;
    }
    oBox1.onmousedown=function(ev){
        var oEvent= ev ||    event;
        
        var disX1=oEvent.clientX-oBox1.offsetLeft;
        var disY1=oEvent.clientY-oBox1.offsetTop;
        document.onmousemove=function(ev){
            var oEvent= ev ||    event;
            var le=oEvent.clientX-disX1;
            var to=oEvent.clientY-disY1;
            oBox1.style.left=le+'px'    ;
            oBox1.style.top=to+'px'    ;
            if(collText(oBox,le,to,oBox1)){
                oBox.style.background='red';
            }else{
                oBox.style.background='#000';        
            }
        };
        document.onmouseup=function(){
            document.onmousemove=null;    
            document.onmouseup=null;
            oBox1.reseaseCapture&&oBox1.reseaseCapture();
        }
        
        oBox1.setCapture&&oBox1.setCapture();
        return false;
    }
}
</script>
</head>

<body>
<div id="box"></div>
<div id="box1"></div>
</body>
</html>
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原文地址：https://www.cnblogs.com/jasonwang2y60/p/6083949.html