QPainter::begin: Paint device returned engine == 0, type: 2

[hsfougaris]

This is a long shot given the nature of my problem, but can anyone here help me debug this message I'm seeing in my debug output?
QPainter::begin: Paint device returned engine == 0, type: 2

It occurs when I add about 10 columns with checkboxes to a QTreeView and QTreeWidget, and I hover over the columns or resize them.

I tried first with a QTreeWidget and creating everything manually (like calling setItemWidget(..) with a QCheckBox as an argument.
I then tried it with a QStandardItemModel by adding QStandardItems with setCheckable set to true.

I get the exact same behaviour: a few messages like that every now and then.
The actual functionality of the form and control don't seem to be affected; Should I just ignore it?
I am running under Windows 7/64 bit with QtCreator 2.1 (my app is not 64 bit).

Thank you,
Harry Sfougaris

[ZapB]

Have you tried debugging into Qt to see what causes this message (you'll need a debug build of Qt)? Can you provide a small compilable example that reproduces this please?

[shiroki]

I agree with ZapB. You have to provide a compilable example or a backtrace for this issue. without seeing the code, it's impossible to tell what the problem is.

[hsfougaris]

Ok, here it is.

Since I can't attach the project:
It's a simple project, the one creator generates.
I added in designer a treeview to the MainWindow and laid it out vertically.

mainwindow.h
@
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QStandardItemModel>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

private:
Ui::MainWindow *ui;
void prepareDataSrc();
QStandardItemModel *dataSrc;
};

#endif // MAINWINDOW_H
@

mainwindow.cpp:
@
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QStandardItem>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
dataSrc = new QStandardItemModel();
prepareDataSrc();
ui->tVw->setModel(dataSrc);
ui->tVw->expandAll();
ui->tVw->setColumnWidth(0, 250);
}

void MainWindow::prepareDataSrc(){
QStringList hdr;
hdr << "Descr" << "Col0" << "Col1" << "Col2" << "Col3" << "Col4" << "Col5" << "Col6" << "Col7" << "Col8" << "Col9";

dataSrc->setHorizontalHeaderLabels(hdr);

for (int i = 0; i < 100; i++) {
    QList<QStandardItem*> iRow;
    QStandardItem *iDescr = new QStandardItem();
    iDescr->setText( QString("Item #%1").arg(i));
    iDescr->setEditable(false);
    iDescr->setData(i, Qt::UserRole);

    iRow << iDescr;
    for (int i2 = 0; i2 < 10; i2++) {
        QStandardItem *_i = new QStandardItem();
        _i->setCheckable(true);
        _i->setEditable(false);
        _i->setTristate(false);
        _i->setData(i2, Qt::UserRole);
         _i->setCheckState(Qt::Checked);
         iRow << _i;
    }
    if (iDescr->hasChildren()) {
        QFont f = iDescr->font();
        f.setBold(true);
        iDescr->setFont(f);
    }
    dataSrc->invisibleRootItem()->appendRow(iRow);
}

}

MainWindow::~MainWindow()
{
delete ui;
}
@

main.cpp:
@
#include <QtGui/QApplication>
#include "mainwindow.h"
#include <QTextCodec>

int main(int argc, char *argv[])
{
QString c = "UTF-8";
QTextCodec::setCodecForTr(QTextCodec::codecForName(c.toLatin1()));
QTextCodec::setCodecForCStrings(QTextCodec::codecForName(c.toLatin1()));
QTextCodec::setCodecForLocale(QTextCodec::codecForName(c.toLatin1()));

QApplication a(argc, argv);
MainWindow w;
w.show();

return a.exec();

}
@

This reproduces it for me.
Thank you,
Harry

[ZapB]

I have tried it here (Gentoo Linux, Qt 4.7.2, raster paint engine) and I get no warnings at all from your example.

What version of Qt are you using? Did you build it yourself or is it a pre-compiled binary distribution of Qt? What paint engine are you using?

[hsfougaris]

I am running under Windows 7/64 bit with QtCreator 2.1.
I am using the pre-compiled binary distribution from Qt.

Paint engine? I don't know what you mean... I haven't done anything to explicitly use a particular engine.

[ZapB]

OK so you are likely using the raster paint engine then as that is the default on Windows.

Which version of Qt though? 4.7.0, 4.7.1, 4.7.2? Something older?

[hsfougaris]

I'm sorry I missed to specify it... 4.7.2

[giesbert]

Hi,

on windows using MSVS 2008 and pre build binaries, on Win7 32 bit, I can't reproduce this behavior.
But if you look at the Qt code it is printed out, when

@
bool QPainter::begin(QPaintDevice *pd)
{
....

d->engine = pd->paintEngine();

if (!d->engine) {
    qWarning("QPainter::begin: Paint device returned engine == 0, type: %d", pd->devType());
    return false;
}

....

@

It could perhaps be a 64 bit issue.

[hsfougaris]

But my app isn't a 64 bit app...
Thankfully whatever it misses to paint is not visible, but it's still strange...

[giesbert]

But you are using 64 but win 7.
Ups sorry, my system is win XP, not win 7

[hsfougaris]

So I guess this needs to be verified by someone running Win7/64 bit, to see if it can be reproduced...

[hsfougaris]

can anyone running Win7/64 bit, please run the above code to see if it can be reproduce?

[pinkieiknip]

Just tried this with W7/64 on Qt 4.8.3 MinGW distribution, no messages or warnings running this code. Also tried 4.7.4 MinGW distribution, no warnings there. It shows the items properly, the checkboxes and list also behave properly.