How to draw circles and rectangles using JavaScript
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>
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