public void request_image (ClipboardImageReceivedFunc callback)
Requests the contents of the clipboard as image.
When the image is later received, it will be converted to a Pixbuf, and
callback will be called.
pixbuf parameter to
callback will contain the resulting
Pixbuf if the request succeeded, or null if it failed. This could happen for various reasons, in
particular if the clipboard was empty or if the contents of the clipboard could not be converted into an image.
a function to call when the image is received, or the retrieval fails. (It will always be called one way or the other.)
user data to pass to