求老师解答
var clippingRegion={x:200,y:200,r:50}
context.arc(clippingRegion.x,clippingRegion.y,clippingRegion.r,Math.PI*2,false);
这样定义之后会出现 Cannot read property 'x' of undefined。
如果将context.arc()里面的参数直接写数字又没问题 为什么呢
Lure丶
2016-01-30
2 回答
var canvsWidth = 800;
var canvsHeight = 600;
var canvas = document.getElementById("canvas");
var cantext = canvas.getContext("2d");
canvas.width = canvsWidth;
canvas.height = canvsHeight;
var image = new Image();
var clippingRegion={x: 400 , y: 200 , r:200 }
image.src = "image.jpg";
image.onload=function(e){
initCanvas();
}
function initCanvas(){
draw(image, clippingRegion);
}
function setClippingRegion(){
cantext.beginPath();
cantext.arc(clippingRegion.x , clippingRegion.y , clippingRegion.r , 0 ,Math.PI*2 , false);
cantext.clip();
}
function draw(image, clippingRegion){
cantext.clearRect( 0, 0,canvas.width,canvas.height);
cantext.save();
setClippingRegion(clippingRegion);
cantext.drawImage(image , 0, 0);
cantext.restore();
}
function show(){
var clippingRegion.r=1000;
alert(clippingRegion.r);
draw(image, clippingRegion);
}为啥我设置了clip的半径为1000画面不起作用呀？
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