Cesium：为图形添加边框

翻遍Cesium文档未能发现border相关内容，但src支持canvas格式索性通过canvas添加图片。

/**
 * 为图形添加边框
 * @param entity cesium实体
 * @param url 图片地址
 * @param color 边框颜色
 */
export const addBorderToImage = (entity, url,color = 'green') => {
  const canvas = document.createElement('canvas');
  canvas.width = entity.billboard.width
  canvas.height = entity.billboard.height
  const ctx = canvas.getContext('2d')
  let image = new Image()
  image.crossOrigin = "anonymous";
  image.width = canvas.width
  image.height = canvas.height
  image.onload = () => {
    ctx.drawImage(image,0,0, canvas.width, canvas.height)
    ctx.strokeStyle = color
    ctx.lineWidth = 6
    ctx.rect(0,0,canvas.width,canvas.height)
    ctx.stroke()
    entity.billboard.image = canvas
  }
  image.src = url
}