代码Canvas.htm
<!DOCTYPE html>
<html lang="en">
<head>
<title>canvas简单应用画各种图形状</title>
</head>
<!--<script language="javascript" src="jquery-1.8.3.js"></script>-->
<script language="javascript" type="text/javascript">
//通过画线段构造三角形
function draw_triangle(x1,y1,x2,y2,x3,y3){
var c = document.getElementById("canvas1");
var cxt = c.getContext("2d");
cxt.moveTo(x1,y1);
cxt.lineTo(x2,y2);
cxt.lineTo(x3,y3);
cxt.lineTo(x1,y1);
cxt.stroke();
}
//画三角进一步封装
function draw(){
draw_triangle(100,50,300,200,150,100);
}
//向canvas原型对象添加画扇形方法
CanvasRenderingContext2D.prototype.selector=function(x,y,radius,sDeg,eDeg){
//保存初始状态
this.save();
// 位移到目标点
this.translate(x, y);
this.beginPath();
// 画出圆弧
this.arc(0,0,radius,sDeg, eDeg);
// 再次保存以备旋转
this.save();
// 旋转至起始角度
this.rotate(eDeg);
// 移动到终点，准备连接终点与圆心
this.moveTo(radius,0);
// 连接到圆心
this.lineTo(0,0);
// 还原
this.restore();
// 旋转至起点角度
this.rotate(sDeg);
// 从圆心连接到起点
this.lineTo(radius,0);
this.closePath();
// 还原到最初保存的状态
this.restore();
return this;
}
function b(){
var c = document.getElementById("canvas1");
var cxt = c.getContext("2d");
//画线
/**cxt.moveTo(10,10);
cxt.lineTo(60,80);
cxt.stroke();**/
//画图片
/*cxt.beginPath();
var img = new Image();
img.src = 'b.jpg';
img.onload=function(){
cxt.drawImage(img,0,0);*/
//画圆环
/*cxt.clearRect(0,0,1200,400);
cxt.beginPath();
cxt.arc(300,100,60,Math.PI*2,false);
cxt.closePath();
cxt.fill();
cxt.fillStyle="white";
cxt.beginPath();
cxt.arc(300,100,50,Math.PI*2,false);
cxt.closePath();
cxt.fill();*/
//画圆弧
cxt.selector(100,100,50,0,Math.PI*0.75);
}
</script>
<body onload="b();">
<!--<canvas id="cans" width="500px" height="300px" style="border:1px solid red;">浏览器不支持canvas</canvas>-->
<canvas id="canvas1" width="1200" height="400" style="border:1px solid red">浏览器不支持该功能</canvas>
<button onclick="draw()">start</button>
</body>
</html>
运行效果：三角和圆弧
