[sane-devel] sane_control_option question

[Henning Meier-Geinitz]

Hi,

On Fri, Oct 14, 2005 at 12:20:44AM -0400, Fred Odendaal wrote:
> The SANE API defines the sane_control_option as:
> 
> SANE_Status sane_control_option (SANE_Handle h, SANE_Int n,
>                                 SANE_Action a, void *v,
>                                 SANE_Int * i);
> 
> Where the argument i is used to convey information back to the frontend. 
> How do I tell the front end to reload options (SANE_INFO_RELOAD_OPTIONS) 
> when it supplies a null argument for i?

You can't. If the frontend send NULL, it's not interested in reloading
the options.

> I want to have the user set the y resolution and have the x resolution 
> automatically update correspondingly. This works  for xscanimage, but 
> not xsane.

I'm a bit surprised that xsane send NULL. Are you sure that his is the
case? At least for the "normal" options it honors reload requests.

If the x resolution directly depends on y, can't you just use one
resolution (option "resolution") and set the other one in the backend
accordingly?

Typically "resolution" means "X resolution". E.g. for most scanners
supported by the gt68xx backend you can select these resolutions:

Resolution    X      Y
100           100    100
300           300    300
600           600    600
1200          600    1200

So only one resolution is selected by the frontend and the backend
decides which X and Y resolutions it uses.

Bye,
  Henning