用clip剪輯之后會(huì)有一個(gè)黑色的圓圈
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
canvas.width=800;
canvas.height=600;
context.arc(100,75,50,0*Math.PI,2.5*Math.PI);
context.stroke();
context.clip();
var img = new Image();
img.src="1.jpg";
img.onload=function(){
context.drawImage(img,0,0);
context.stroke();
}
