[sane-devel] bug in test backend

Henning Meier-Geinitz henning@meier-geinitz.de
Wed, 18 Dec 2002 18:06:04 +0100


On Wed, Dec 18, 2002 at 05:01:34PM +0100, Oliver Rauch wrote:
> > Have I said before that I don't like the double meaning of
> > sane_cancel ("stop current action" + "this was the last scan in a
> > series")? :-)
> >
> > The frame is over after EOF. So why do we need sane_cancel here in
> > normal operation?
> I think the intention is to make sure that the backend nows that the
> frontend will not ask for any additional images.
> What I remember about some discussions with David Mosberger and Andreas Beck 
> is the following example:
> we have a scanner that produces several images at the same time.
> - sane_start is called the first time => e.g. 10 images are scanned at the 
> same time.
> - sane_read until EOF => first image is transmitted to the frontend
> - sane_start
> - sane_read until EOF => second image is transmitted to the frontend
> when the frontend does not ask for more images and does not call sane_cancel 
> then the backend does not know that it can throw awy the last eight images.
> so a sane_start indicates: give me more
> a sane_cancel indicates: throw away the rest.

I see. However the rest of the standard (v1) doesn't say anything about
multiple images as far as I know. So how can the frontend know about