putImageData重新渲染像素，无法实现透明?
const createPixel = this.ctx.getImageData(this.pikaqiuX, this.pikaqiuY, 280, 280) let data = createPixel.data; let average = 0; for (let i = 0; i < data.length; i+=4) { data[i+3] = 0 } this.ctx.putImageData(createPixel, this.pikaqiuX, this.pikaqiuY) 把a设置为0，在开发工具上可以透明图像， 在预览中没有发生变化
