图片一些转换和处理

/** 将url转化为img对象 */
export function urltoImage(url, fn) {
  var img = new Image()
  img.src = url
  return img
}
/** img对象转化为canvas对象 */
export function imagetoCanvas(image) {
  var cvs = document.createElement('canvas')
  var ctx = cvs.getContext('2d')
  cvs.width = image.width
  cvs.height = image.height
  ctx.drawImage(image, 0, 0, cvs.width, cvs.height)
  return cvs
}
//quality图片压缩质量，前端压缩的话，可以用到这个属性
export function canvasToDataURL(canvas, format, quality) {
  return canvas.toDataURL(format || 'image/jpeg', quality || 1.0)
}