canvas绘制圆角头像

如果你想绘制的网页包含一个圆弧形的头像的canvas图片,但是头像本身是正方形的,需要的方法如下:
首先, 拿到头像在画布上的坐标和宽高:(具体怎么获取不在此做具体介绍)

let {avatarX, avatarY, avatarW, avatarH} = {20, 20, 80, 80};

然后 只需要调用以下函数即可:

let Canvas = document.createElement('canvas');
let ctx = Canvas.getContext("2d");
let avatar = new Image();
avatar.src = '../src/xx.png';
avatar.onload = (scaleBy = 2) => {
   circleImg(ctx, avatar, avatarX * scaleBy, avatarY * scaleBy, avatarW * scaleBy / 2);
}

// r: 半径
function circleImg(ctx, img, x, y, r) {
    ctx.save();
    var d =2 * r;
    var cx = x + r;
    var cy = y + r;
    ctx.arc(cx, cy, r, 0, 2 * Math.PI);
    ctx.clip();
    ctx.drawImage(img, x, y, d, d);
    ctx.restore();
}

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