[SOLVED] Why QPrinter need QtGUI

Pitchou

Hi everyone
I would to know why I must have a X11 server connection to use the QPrinter Class. In Qt 4.3, I wrote a programm which use Qprinter without the GUI and it works well.
But I need to compile it on a new platform which has Qt 4.6 and it doesn't work because of the GUI.

DO you have an answer ?
Thanks

bjanuario

Did u mention on .pro file that your project is a console ?
If so can you reproduce the error ?

Pitchou

Hi. yes, my .pro file has the console config.

@QT += core

TARGET = ptest
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app@

To use QPrinter (with Qt > 4.4), it needs QPaintDevice. This one needs QApplication which needs a server X connexion. That is I have deduced by testing only QPrinter in a test programm like this :

@#include <QtCore/QCoreApplication>
#include <Qt/qprinter.h>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
cout << "step 1" << endl;
QPrinter pt(QPrinter::HighResolution);
cout << "step 2" << endl;
}@

The programm abord before the step 2 :

bq. step 1
QPrinter: Must construct a QApplication before a QPaintDevice
Aborted

I don't know how to fix it because I can't change Qt version on the server and I think there isn't a "QPrinter like" class which do the same thing without needing server X connexion...

bjanuario

QPrint is now a QWidget class, so you are not able to print without gui. But you can do in a old fashion c++ way. Here some sample:
@#include <iostream.h>
#include <fstream.h>
#include <conio.h>

void main(void)
{
clrscr();
char filename[13];
char ch;
cout<<"\nEnter the text file name:";
cin.getline(filename,13);
cout<<"\n";
ifstream fin(filename, ios::in);
if(!fin)
{
cerr<<"\n Cannot open file !\n";
getch();
return;
}
char const * const PrinterName = "usb001:"; // Identify the printer port.
ofstream printer(PrinterName); // Open the printer stream.
if(!printer) // Ensure the printer stream opened ok.
{
cerr << "\a\n\tERROR: Unable to open " << PrinterName << endl;
cout << "\n\tPress the [ENTER] key to return ";
getch();
return;
}

while (! fin.eof())
{
    fin.get(ch);
    printer << (ch);
}

printer << endl << ends << flush;
printer.close(); // Finish the print job by closing the printer stream.
fin.close();

// Send a carriage return and a formfeed to the printer so that: a) this
// print job is ejected from the printer, and b) the next print job starts
// at the top left corner of the page.

fin.close(); // Close file./
cout << "\n\n\t\t\t\Printing...";
cout << "\n\n\ Please press the [ENTER] key to return";
getch();

return;

}@

AcerExtensa

You can't print without GUI using any of known printing library... GhostScript also needs X libraries... You can use framebuffers to do it in console mode, but you will need GUI libs in any way....

P.S.: Only Dot Printers do not need GUI to print ;)

bjanuario

[quote author="AcerExtensa" date="1370616218"]You can't print without GUI using any of known printing library... GhostScript also needs X libraries... You can use framebuffers to do it in console mode, but you will need GUI libs in any way....

P.S.: Only Dot Printers do not need GUI to print ;)[/quote]

U can print in Linux in every kind of printer without gui! U just need to have proper driver on kernel if not paralel or serial printer, is nothing to do about if is a dot printer or laser ... it's the port and driver issues.

AcerExtensa

@
[quote author="bjanuario" date="1370619483"]
U can print in Linux in every kind of printer without gui! U just need to have proper driver on kernel if not paralel or serial printer, is nothing to do about if is a dot printer or laser ... it's the port and driver issues.[/quote]
@

No, you can't :) all console printers uses framebuffers.... sure you can send to printer some kind of scratch and let print it, but we a talking not just physical printing... you can't generate print-page without X!

bjanuario

If u use graphics, for sure this will be kind tricky, but some printers support decode chars that then print graphics even without X, for text is straight on. I can assure u because we use this on linux ;) On windows i dunno if is possible ...

[quote author="AcerExtensa" date="1370639879"]@
[quote author="bjanuario" date="1370619483"]
U can print in Linux in every kind of printer without gui! U just need to have proper driver on kernel if not paralel or serial printer, is nothing to do about if is a dot printer or laser ... it's the port and driver issues.[/quote]
@

No, you can't :) all console printers uses framebuffers.... sure you can send to printer some kind of scratch and let print it, but we a talking not just physical printing... you can't generate print-page without X! [/quote]

AcerExtensa

Tell us what do you use and how do you do it! Maybe you have something what peoples with PostScript printers all other the world are looking for...

Pitchou

So, if I undestand what you said... Before Qt4.4, it was possible to use QPrinter to generate a PDF file but now, with Qt I can't print a PDF file with QPrinter if my Linux doesn't have a GUI ? ...

Do you know another way to print a QImage in a PDF file, without using GUI ?

AcerExtensa

QImage and QPrinter inherits QPaintDevice, and QPaintDevice is an GUI Class. So you need QtGUI library if you would like to use this two classes.

Pitchou

I have QtGUI library installed on the OS which is OpenSuse 11. But it's a server OS and it doesn't have server X connexion ...

So, I'm happy :/ My app can't work on the server.

Thanks for your answer.

AcerExtensa

you can still use virtual framebuffer like Xvfb

Pitchou

Thanks AcerExtensa ! XVFB was a good idea and now, the app works well ! :D
This thread can be closed

AcerExtensa

Please add prefix "[SOLVED]" to the left of the topic subject. Thanks!

fernando.lopes

Hi Pitchou.
How did you use XVFB to create the QPrinter?

I need to make a PDF printer in a console application and I get the same error you got.

Pitchou

Hi Fernando, I changed my way. I do not use XVFB anymore because I found a solution to use QPriner without serverX.

My error was to use QApplication, which require a serverX. I found a trick !

When you use QApplication, I think you use it like this :
@QApplication a(argc, argv,);@

Change it to have something like this : @QApplication a(argc, argv, false);@

The false attribute will force the program to work without a serverX and you can use QPrinter without any problem

fernando.lopes

Thank you Pitchou!
It is working now! :D