window.onload?=?function(){
????var?canvasWidth?=?800;
????var?canvasHeight?=?600;
????var?canvas?=?document.getElementById("canvas");
????var?context?=?canvas.getContext("2d");
????canvas.width?=?canvasWidth;
????canvas.height?=?canvasHeight;
????var?image?=?new?Image();
????var?clippingRegion?=?{x:400,y:200,r:50};
????image.src?=?"img/293731.jpg";
????image.onload?=?function?(e)?{
????????initCanvas();
????????//context.drawImage(image,0,0);
????}
????//
????function?initCanvas(){
????????draw(Image,clippingRegion);
????}
????function?setCliippingRegion(clippingRegion){
????????context.beginPath();
????????context.arc(clippingRegion.x,clippingRegion.y,clippingRegion.r,0,Math.PI*2,false);
????????context.clip();
????}
????function?draw(image,clippingRegion){
????????context.clearRect(0,0,canvas.width,canvas.height);
????????context.save();
????????setCliippingRegion(clippingRegion);
????????context.drawImage(image,0,0);
????????context.restore();
????}
}
2016-08-05
函數(shù)與函數(shù)之間存在訪問(wèn)域的問(wèn)題，window.onload是將頁(yè)面全部加載完成，包括圖片，image.onload也是圖片加載，重復(fù)使用不好，去掉window.onload試試