let setupCanvas = (): CanvasRenderingContext2D => {
let canvas = <HTMLCanvasElement>document.getElementById("myCanvasContainer");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
let _oldWidth = canvas.width;
let _oldHeight = canvas.height;
let dpr = window.devicePixelRatio || 1;
let rect = canvas.getBoundingClientRect();
canvas.width = rect.width * dpr;
canvas.height = rect.height * dpr;
canvas.style.width = `${_oldWidth}px`;
canvas.style.height = `${_oldHeight}px`;
let ctx = canvas.getContext('2d');
ctx.scale(dpr, dpr);
return ctx;
};
js canvas在高dpi设备上绘制