文字居中：ctx.textAlign = "center";

元素居中：ctx.arc(screenWidth / 2, 122, 40, 0, 2 * Math.PI);

ctx.arc()的x轴为当前屏幕的宽度/2；

let screenWidth = 540;
let screenHeight = 960;
// 头像
if (photoimg) {ctx.setFillStyle('#000000')ctx.save();ctx.beginPath() //开始创建一个路径ctx.arc(screenWidth / 2, 122, 40, 0, 2 * Math.PI) //画一个圆形裁剪区域ctx.strokeStyle = 'transparent';ctx.stroke();ctx.clip() //裁剪ctx.drawImage(photoimg, 230, 82, 80, 80);ctx.restore()	
}// 昵称
if (that.userInfo) {let names = that.userInfo.nicknamectx.setFontSize(28);ctx.setFillStyle('#333333')ctx.font = 'normal blod 28px PingFangSC, PingFang SC';ctx.textAlign = "center"let titleW = ctx.measureText(names)ctx.fillText(names, screenWidth / 2, 196);
}