处理谷歌地图marker旋转

/*
* 功能：使用canvas旋转图标，并生成路径
* 参数：options（Object）
* 用途：处理谷歌地图marker旋转
* */
const setRotation = (options) => {
  return new Promise((resolve, reject) => {
    let w = options.width || 40
    let h = options.height || 40
    let canvas = document.createElement('canvas')
    canvas.width = w
    canvas.height = h
    let ctx = canvas.getContext('2d')
    let angle = options.deg ? options.deg * Math.PI / 180 : 0
    let centerX = w / 2
    let centerY = h / 2
    let dataURL = ''
    let img = new Image()
    img.src = options.url
    img.onload = function() {
      ctx.clearRect(0, 0, w, h)
      ctx.save()
      ctx.translate(centerX, centerY)
      ctx.rotate(angle)
      ctx.translate(-centerX, -centerY)
      ctx.drawImage(img, centerX/2, 0)
      ctx.restore()
      dataURL = canvas.toDataURL('image/png')
      resolve({
        size: options.size,
        origin: options.origin,
        url: dataURL
      })
    }
  })
}