[Kde-graphics-devel] Re: Using libksane from a non-graphical application

[Ben Martin]

On Wed, 2011-04-27 at 10:09 +0300, Kåre Särs wrote:
> On Tuesday 26 April 2011 13:26:25 Ben Martin wrote:
> > Hi,
> >   I decided to allow libferris to mount scanners at long last. The
> > basics of this exposure is to configure sane and grab an image to jpg or
> > png. The code in skanlite does very similar things, but as a filesystem
> > I don't create any graphical interface. 
> > 
> >   It turns out that things work well from the console, though the calls
> > to KMessageBox::sorry() in KSaneWidgetPrivate::oneFinalScanDone() are
> > quite deadly as the dialog is not shown and the whole thing seems to
> > hang there. A visit to gdb shows that the dialog is up and not shown in
> > the backtrace.
> > 
> >   Inside imageReady() I call scanCancel() to try to avoid these
> > KMessageBoxes but it seems I get two scanDone() signals anyway and the
> > second one complains that the ADF is out of ammo and thus the
> > KMessageBox is attempted by libksane.
> 
> I guess it would not bee to much of a problem to disable those message boxes.

I have them disabled locally. I'm not sure what the desired KDE way for
a more standing fix is. My first thought was the make them generated in
a virtual method in ksane, or maybe as a callback which you can set to
override.

The other idea might be to have ksane check if the qapplication instance
is graphical or not... or just have a setShowErrorsOnConsole( bool )
maybe?

> 
> I have a hunch that you will need an X server running to be able to create a 
> QWidget... 

This seemed to be one of the downsides, that and requiring the linking
of GUI code to get at the scanner. But its probably better to try to
refactor ksane at some stage than write my own sane wrapper from
scratch.

> 
> > 
> >   About the only other thing I see that would be handy is a 
> > QList< QString > getDeviceNames() const;
> > sort of method to enumerate the scanners. This assumes that there is any
> > interest in allowing non graphical clients to pick at libksane. Other
> > than that libksane allows fairly straightforward scanning from the
> > console. :)
> 
> "QList< QString > getDeviceNames() const;" is actually a feature that I have 
> had in the plans for some time, but I have not had enough of an itch to do it 
> (nobody using it). It should not be a big problem to implement.
> 
> The proper way to it would be to have a "void initGetDeviceList() const;" that 
> initiates the thread and a signal that returns the device list. This because 
> the getting of the list can take several seconds. Then a convenience function 
> that sits and waits for the signal to be returned.
> 
> I'll add an entry to the feature plan before the soft freeze and we can check 
> what it needs to disable the dialogs and add the getDeviceNames().

Well, I had hacked together a sync method as above. The patch uses the
async init() and signal that is the much nicer design. So now half the
things are done :)

Though you'll want to remove my commenting out the kmessagebox lines in
the patch.

> 
> 
> 
> > 
> > (oh, I'm not on list, please CC relies if any).
> 
> Sure, I'm happy if somebody wants to use/improve libksane :)

Thanks for creating & working on it! It definitely made adding scanner
support fairly quick. libksane is the code (updated to use the attached
patch) that I used to add this:
http://monkeyiq.blogspot.com/2011/04/blocking-nostril.html

> 
> > 
> > 
> 
> /Kåre
> 

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