[Development] Adding CPD support to Qt print dialog

[Tor Arne Vestbø]

> On 23 Sep 2022, at 19:21+02:00, Gaurav Guleria <gaurav.gen3 at gmail.com> wrote:
> 
> As far as I know, the CUPS is currently implemented in Qt at two different places: src/plugins/printsupport/cups/ and directly within the dialog src/printsupport/dialogs/qprintdialog_unix.cpp. By implementing CPDB support as a plugin, does it mean that we create a similar src/plugins/printsupport/cpdb which uses CPDB to enumerate printers instead of CUPS? If so, what about the unix print dialog, don't we need to add the CPDB code there too (#if QT_CONFIG(cpdb) ... #endif constructs, just like CUPS)?

The QCupsJobWidget is documented as "a widget to add to QPrintDialog to enable extra CUPS options such as Job Scheduling, Job Priority or Job Billing”, so I don’t think having any CPDB specific code in the UNIX print dialog is required as a first step to bring a CPDB print backend up.

Once we get to that point we can look at possibly adding new API for the print engines to deal with the needs of QCupsJobWidget and the like, so that we don’t need CUPS/CPDB specifics in the dialog code.

Cheers,
Tor Arne

> 
> On 9/19/22 21:59, Tor Arne Vestbø wrote:
>> 
>>> On 19 Sep 2022, at 18:21, Till Kamppeter <till.kamppeter at gmail.com> wrote:
>>> 
>>> On 19/09/2022 15:43, Tor Arne Vestbø wrote:
>>>>> First is to create a new Qt print backend, what, instead of communicating directly with CUPS, communicates with the CPDB backends. It is some kind of "middle end", on one end being a Qt print backend and on the other end being a CPDB frontend.''
>>>> This sounds like a good first step. It doesn’t involve any of the GUI bits, just the enumeration and communication with the various CPDB-exposed printers.
>>>> Since the QtPrintSupport module doesn’t depend on DBUS today (AFAIK), the CPDB print backend should be a plugin.
>>>> 
>>> OK, Gaurav so you should be able to provide the CPDB support as a plugin (Tor, is this a Qt print backend like the one for CUPS for example?).
>> Correct. Note that for Qt 6, some of the print engines that were previously plugins were moved into the QtPrintSupport library directly, such as the macOS print engine, but the interface for enumerating these from Qt’s point of view is still as print engine “plugins”. The CUPS engine is a fully standalone plugin, so it’s a good basis for the CPDB work.
>> 
>> Cheers,
>> Tor Arne
>> 
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