Exports a Surface to an image. To do this,
the svg string must be sent to a remote server and processed.
Sending the data
A post request is made to the URL. The following fields are sent:
- width: The width of the image
- height: The height of the image
- type: The image type to save as, see supportedTypes
- svg: The svg string for the surface
It is expected that the user will be prompted with an image download.
As such, the following options should be set on the server:
- Content-Disposition: 'attachment, filename="chart.png"'
- Content-Type: 'image/png'
Important: By default, chart data is sent to a server operated
by Sencha to do data processing. You may change this default by
setting the defaultUrl of this class.