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Home  >  Article  >  Web Front-end  >  How to draw circles and rectangles using JavaScript

How to draw circles and rectangles using JavaScript

巴扎黑
巴扎黑Original
2017-09-14 11:53:222435browse

本文实例讲述了js绘制圆形和矩形的方法。分享给大家供大家参考。具体如下：

这里使用js来绘制圆形和矩形，支持选择图形的背景颜色，同时可设置圆角矩形、半径、正圆、矩形、正方形这几个选项。或许这些图形你不需要，但重要的是让你学会JavaScript绘制图形的方法，这是要表达的核心。

运行效果如下图所示：

具体代码如下：

<!doctype html>
<html>
<head>
<title>js来绘制圆形和矩形</title>
<style>
 *{margin:0; padding:0;}
 #p{position:absolute; background:#ccc;}
 .sel{ margin:30px auto; width:960px; overflow:hidden}
 li{ list-style:none; float:left; width:60px; height:20px;}
 #colors{ width:500px; float:left}
 .selColor{ float:left}
 #radius{ width:40px; height:20px;}
 .red{background:red;}
 .yellow{background:yellow;}
 .blue{background:blue;}
 .pink{background:pink;}
 .black{background:black;}
 .orange{background:orange;}
 .green{ background:green;}
 .xz{ width:340px; float:right;}
 #canvas{ width:960px; height:500px; border:1px solid #ccc; margin:0 auto}
</style>
<script>
function $Id(id)
{
 return document.getElementById(id); 
}
window.onload=function(){
 var oCanvas=$Id("canvas");
 var oRoud=$Id("roud");
 var oRadius=$Id("radius");
 var oCir=$Id("circle");
 var oSqu=$Id("squ");
 var oColors=$Id("colors");
 var aColors=oColors.getElementsByTagName("li");
 var color="red";
 var aInputs=document.getElementsByTagName("input");
 var xz="roud";
 var arr=[];
 for(var i=0;i<aInputs.length;i++)
 {
  if(aInputs[i].type=="checkbox")
  {
   arr.push(aInputs[i]); 
  }
 }
 for(var i=0;i<arr.length;i++)
 {
  arr[i].onclick=function()
  {
   if(!this.checked)
   {
    this.checked=false; 
   }
   else
   {
    for(var j=0;j<arr.length;j++)
    {
     arr[j].checked=false; 
    }
    this.checked=true; 
    xz=this.value;
   }
  } 
 }
 //选择颜色
 for(var i=0;i<aColors.length;i++)
 {
  aColors[i].onclick=function()
  {
   color=this.className; 
  } 
 }
 oCanvas.onmousedown=function(ev)
 {
   if(oCanvas.setCapture)
   {
    oCanvas.setCapture();
   }
   for(var i=0;i<arr.length;i++)
   {
    if(arr[i].checked)
    {
     arr[i].checked=true;
     xz= arr[i].value;
    } 
   }
   var oEv=ev||window.event;
   var disX=oEv.clientX;
   var disY=oEv.clientY;
   var oR=document.createElement("p");
   oR.id="p";
   oR.style.top=disY+"px";
   oR.style.left=disX+"px";
   oR.style.backgroundColor=color;
   document.body.appendChild(oR);
  document.onmousemove=function(ev)
  {
   var oEv=ev||window.event;
   var x=oEv.clientX;
   var y=oEv.clientY;
   if(x<oCanvas.offsetLeft)
   {
    x=oCanvas.offsetLeft; 
   }
   else if(x>oCanvas.offsetLeft+oCanvas.offsetWidth)
   {
    x=oCanvas.offsetLeft+oCanvas.offsetWidth
   }
   if(y<oCanvas.offsetTop)
   {
    y=oCanvas.offsetTop; 
   }
   else if(y>oCanvas.offsetTop+oCanvas.offsetHeight)
   {
    y=oCanvas.offsetTop+oCanvas.offsetHeight
   }
   oR.style.width=Math.abs(x-disX)+"px";
   oR.style.top=Math.min(disY,y)+"px";
   oR.style.left=Math.min(disX,x)+"px";
   switch(xz)
   {
    case "roud":
     oR.style.height=Math.abs(y-disY)+"px";
     oR.style.borderRadius=oRadius.value+"px";
     break; 
    case "circle":
     oR.style.height=Math.min(Math.abs(x-disX),Math.abs(y-disY))+"px";
     oR.style.width=Math.min(Math.abs(x-disX),Math.abs(y-disY))+"px";
     oR.style.borderRadius=(Math.min(Math.abs(x-disX),Math.abs(y-disY)))/2+"px";
     break;
    case "squ":
     oR.style.height=Math.abs(y-disY)+"px";
     break;
    case "square":
     oR.style.height=Math.min(Math.abs(x-disX),Math.abs(y-disY))+"px";
     oR.style.width=Math.min(Math.abs(x-disX),Math.abs(y-disY))+"px";
   }
  }
  document.onmouseup=function()
  {
   document.onmousemove=null;
   document.onmouseout=null;
   if(oCanvas.releaseCapture)
   {
    oCanvas.releaseCapture();
   } 
  }
  return false;
 }
}
</script>
</head>
<body>
 <p class="sel">
  <span class="selColor">请选择一种颜色</span>
 <ul id="colors">
  <li value="red" class="red"></li>
  <li value="yellow" class="yellow"></li>
  <li value="blue" class="blue"></li>
  <li value="pink" class="pink"></li>
  <li value="black" class="black"></li>
  <li value="orange" class="orange"></li>
  <li value="green" class="green"></li>
 </ul>
 <p class="xz">
  <input type="checkbox" value="roud" id="roud" />圆角矩形
  <label>半径</label><input type="text" value="" id="radius" />
  <input type="checkbox" id="circle" value="circle" />正圆
  <input type="checkbox" id="squ" value="squ" />矩形
  <input type="checkbox" id="square" value="square" />正方形
  </p>
 </p>
 <p id="canvas">
 </p>
</body>
</html>

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