QPrinter / QPrintDialog issue

[d_stranz]

Using Qt 5.2 on Windows 7 64bit. I am building a 32-bit app

I am trying to get printing working. I have a weird problem that I can't seem to figure out. If I create a QPrinter instance using this code:

QPrinter * pPrinter = new QPrinter( QPrinterInfo::defaultPrinter(), QPrinter::ScreenResolution );

QPrinter * pPrinter = new QPrinter( QPrinterInfo::defaultPrinter(), QPrinter::ScreenResolution );

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and then look at the values for

QPrinter::pageRect( QPrinter::Inch ) and QPrinter::paperRect( QPrinter::Inch )

QPrinter::pageRect( QPrinter::Inch ) and QPrinter::paperRect( QPrinter::Inch )

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I get the results I would expect for my default printer (Letter size paper, 8.5 x 11 inches).

If I then pass this QPrinter instance to QPrintDialog and open it:

if ( pPrinter && pPrinter->isValid() )
{
	QPrintDialog dlg( pPrinter );
	dlg.setOptions( QAbstractPrintDialog::None );
 
	connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
        dlg.exec();
}

if ( pPrinter && pPrinter->isValid() )
{
	QPrintDialog dlg( pPrinter );
	dlg.setOptions( QAbstractPrintDialog::None );

	connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
        dlg.exec();
}

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and then examine those same values in the onPrinterAccepted() slot, those values are now completely messed up, typically QRectF( 0.0, 0.0, -0.0104166, -0.0104166)

This happens even if I do nothing at all with the dialog - let it display, don't do anything except click the "Print" button.

If I create the QPrintDialog without passing it a QPrinter instance:

QPrintDialog dlg;
dlg.setOptions( QAbstractPrintDialog::None );
 
connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
dlg.exec();

QPrintDialog dlg;
dlg.setOptions( QAbstractPrintDialog::None );

connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
dlg.exec();

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I get exactly the same behavior. If I select a different printer from the dialog, it doesn't matter what printer I choose, I still get the same messed up results if I let the dialog use my QPrinter instance or if I look at the one returned to the slot.

Changing the Unit type in the call to

QPrinter::pageRect()

QPrinter::pageRect()

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results in different values being returned, but they are always wrong and always a negative height and width.

I have confirmed that there is only one plugins/printsupport directory on my machine, so it can't be pulling in a mis-matched "windowsprintersupport" DLL

I do not know if it is relevant, but the code that does the printing is in a static library, linked into my app. The Print QAction's triggered() signal in the GUI is connected to a slot in the library that kicks off the printing.

Any ideas what I might be doing wrong?

[d_stranz]

Here's a minimal compilable example to demonstrate the problem. I have attached the PNG file to this post. With the QPrintDialog code commented out (as shown below), I get the results in the attached PDF file using PDFCreator as my default printer.

I would greatly appreciate it if someone could run this code and tell me if it also fails for you when you allow the QPrintDialog code to execute.

// PrintingTestDlg.h:
 
#ifndef PRINTINGTESTDLG_H
#define PRINTINGTESTDLG_H
 
#include <QDialog>
 
class QPrinter;
class QLabel;
 
class PrintingTestDlg : public QDialog
{
	Q_OBJECT
 
public:
	PrintingTestDlg(QWidget *parent = 0);
	~PrintingTestDlg();
 
protected slots:
	void	onPrint();
	void	onPrinterAccepted( QPrinter * pPrinter );
 
private:
	QLabel *	mpLabel;
};
 
#endif // PRINTINGTESTDLG_H

// PrintingTestDlg.h:

#ifndef PRINTINGTESTDLG_H
#define PRINTINGTESTDLG_H

#include <QDialog>

class QPrinter;
class QLabel;

class PrintingTestDlg : public QDialog
{
	Q_OBJECT

public:
	PrintingTestDlg(QWidget *parent = 0);
	~PrintingTestDlg();

protected slots:
	void	onPrint();
	void	onPrinterAccepted( QPrinter * pPrinter );

private:
	QLabel *	mpLabel;
};

#endif // PRINTINGTESTDLG_H

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// PrintingTestDlg.cpp:
 
#include "PrintingTestDlg.h"
 
#include <QHBoxLayout>
#include <QPixmap>
#include <QLabel>
#include <QPushButton>
#include <QPrinter>
#include <QPrinterInfo>
#include <QPrintDialog>
#include <QPainter>
 
PrintingTestDlg::PrintingTestDlg(QWidget *parent)
	: QDialog(parent)
{
	QHBoxLayout *	pLayout = new QHBoxLayout( this );
 
	QPushButton *	pPrintBtn = new QPushButton( this );
	pPrintBtn->setText( "Print" );
 
	pLayout->addWidget( pPrintBtn );
 
	mpLabel = new QLabel( this )	;
	mpLabel->setPixmap( QPixmap( "./logo11w.png" ) );
 
	pLayout->addWidget( mpLabel );
	setLayout( pLayout );
 
	connect( pPrintBtn, SIGNAL( clicked() ), this, SLOT( onPrint() ) );
}
 
PrintingTestDlg::~PrintingTestDlg()
{
}
 
void PrintingTestDlg::onPrint()
{
	QPrinterInfo	printerInfo = QPrinterInfo::defaultPrinter();
 
	QPrinter * pPrinter = 0;
	if ( !printerInfo.isNull() )
		pPrinter = new QPrinter( printerInfo, QPrinter::ScreenResolution );
 
	if ( pPrinter && pPrinter->isValid() )
	{
		QPrintDialog	dlg( pPrinter );
		dlg.setOptions( QAbstractPrintDialog::None );
 
		// With this line un-commented, the printing works correctly for the
		// default printer with default settings
		onPrinterAccepted( pPrinter );
 
		// Un-comment these two lines, and comment out the line above to see what happens
		// when the QPrintDialog is used.
// 		connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
// 		dlg.exec();
 
		delete pPrinter;
	}
}
 
void PrintingTestDlg::onPrinterAccepted( QPrinter * pPrinter )
{
	QString	printName = pPrinter->printerName();
	QRectF	paperRect = pPrinter->paperRect( QPrinter::DevicePixel );
	QRectF	pageRect = pPrinter->pageRect( QPrinter::DevicePixel );
	QRect		plotRect = mpLabel->rect();
 
	double xscale = pageRect.width() / double( plotRect.width() );
	double yscale = pageRect.height() / double( plotRect.height() );
	double scale = qMin( xscale, yscale );
 
	QPainter	painter( pPrinter );
	painter.translate( paperRect.x() + pageRect.width() / 2,
		paperRect.y() + pageRect.height() / 2 );
	painter.scale( scale, scale );
	painter.translate( -plotRect.width() / 2, -plotRect.height() / 2 );
 
	mpLabel->render( &painter );
}

// PrintingTestDlg.cpp:

#include "PrintingTestDlg.h"

#include <QHBoxLayout>
#include <QPixmap>
#include <QLabel>
#include <QPushButton>
#include <QPrinter>
#include <QPrinterInfo>
#include <QPrintDialog>
#include <QPainter>

PrintingTestDlg::PrintingTestDlg(QWidget *parent)
	: QDialog(parent)
{
	QHBoxLayout *	pLayout = new QHBoxLayout( this );

	QPushButton *	pPrintBtn = new QPushButton( this );
	pPrintBtn->setText( "Print" );

	pLayout->addWidget( pPrintBtn );

	mpLabel = new QLabel( this )	;
	mpLabel->setPixmap( QPixmap( "./logo11w.png" ) );

	pLayout->addWidget( mpLabel );
	setLayout( pLayout );

	connect( pPrintBtn, SIGNAL( clicked() ), this, SLOT( onPrint() ) );
}

PrintingTestDlg::~PrintingTestDlg()
{
}

void PrintingTestDlg::onPrint()
{
	QPrinterInfo	printerInfo = QPrinterInfo::defaultPrinter();

	QPrinter * pPrinter = 0;
	if ( !printerInfo.isNull() )
		pPrinter = new QPrinter( printerInfo, QPrinter::ScreenResolution );

	if ( pPrinter && pPrinter->isValid() )
	{
		QPrintDialog	dlg( pPrinter );
		dlg.setOptions( QAbstractPrintDialog::None );

		// With this line un-commented, the printing works correctly for the
		// default printer with default settings
		onPrinterAccepted( pPrinter );

		// Un-comment these two lines, and comment out the line above to see what happens
		// when the QPrintDialog is used.
// 		connect( &dlg, SIGNAL( accepted( QPrinter * ) ), this, SLOT( onPrinterAccepted( QPrinter * ) ) );
// 		dlg.exec();

		delete pPrinter;
	}
}

void PrintingTestDlg::onPrinterAccepted( QPrinter * pPrinter )
{
	QString	printName = pPrinter->printerName();
	QRectF	paperRect = pPrinter->paperRect( QPrinter::DevicePixel );
	QRectF	pageRect = pPrinter->pageRect( QPrinter::DevicePixel );
	QRect		plotRect = mpLabel->rect();

	double xscale = pageRect.width() / double( plotRect.width() );
	double yscale = pageRect.height() / double( plotRect.height() );
	double scale = qMin( xscale, yscale );

	QPainter	painter( pPrinter );
	painter.translate( paperRect.x() + pageRect.width() / 2,
		paperRect.y() + pageRect.height() / 2 );
	painter.scale( scale, scale );
	painter.translate( -plotRect.width() / 2, -plotRect.height() / 2 );

	mpLabel->render( &painter );
}

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