libkdeprint

[John Layt]

Right.

In this e-mail I'll address printFiles() and leave the other issues to 
separate e-mails.

I spent half my day at work today looking through the KDEPrint code to see 
exactly how printFiles does its magic, and I think the solution is fairly 
easy, depending on how fancy we want it to be.

printFiles() takes the list of files to print, then applies any valid 
pre-filters chosen in the print dialog to the files, then passes the file 
list to the specific printer system implementation you are using (CUPS, LPR, 
etc).  The implementation then reads the settings from KPrinter, translates 
them into the printer system specific commandline options, and executes the 
command.

In the case of CUPS, this is a KDEPrint utility found in 
kdelibs/kdeprint/cups/cupsdoprint.c which you pass the printer name, printer 
options and filenames.  It then calls the CUPS api for you and your files 
print.  For LPR the command is obviously 'lpr'.

Now, there's a fair bit of code wrapped around that, most just for nice job 
management, but some to respect the settings chosen in the print dialog.  
This can be found in classes like KPrinterImpl, KCupsPrinterImpl, 
KLprPrinterImpl, KDEPrintD and KPrintProcess.

My proposal is a 3 step one:
1) This is the proof of concept step.  Write a basic printFiles() that takes a 
QPrinter and a file list, reads the printer name from QPrinter, and executes 
cupsdoprint to send all the files to CUPS.  The key thing here is that 
QPrinter::printerName() provides a name usable for CUPS, which it appears to 
do.
2) Add code to detect between CUPS/LPR and add LPR support.
3) Add code to pass along other important settings, like print range and 
copies.

This won't be supported under Windows or OSX (but then the old one didn't work 
either), or other *nix backends like rlpr.  However some file formats 
supported by Okular use the normal QPainter which will be supported, so 
Okular will need to pop up a message telling the users "Sorry this file 
format printing not supported on Win/Mac, but x, y and z do work"

Nice plus is this method will work for any file format supported by CUPS.

Does this all look feasible?  Obviously there is no way it could be completed 
and QA'ed in time to make kdelibs for 4.0, so the 3 apps affected will have 
to include it directly for now, but it will only be a small amount of code.

If no-one else gets there first, I’ll start on this next week.

Another problem is the non-continuous page selection which Qt doesn’t 
support, e.g. selecting random pages from the preview list in KGhostView (I 
don't think Okular currently supports this?).  The work-around is that CUPS 
does support being passed a file and a list of non-continuous pages to print.  
So if a user has selected pages from the GUI, when we display the 
QPrintDialog we set the page range to Selection rather than All.  If they 
leave it at Selection, then we send the full file and the selected list of 
pages to CUPS to do the processing.  If they switch to All or Pages then we 
use those instead.  If they are not using CUPS (e.g. on LPR, Windows or OSX), 
then we first we pop up a message box saying "not supported, select All or a 
continuous range in Pages instead", then show the QPrintDialog with Selection 
disabled.

This is a nice to have but not vital, as the user can stll select continuous 
page ranges instead.

Now I just have to explain to the boss why that design document isn't 
ready :-)

John.

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