[Qt-interest] bug with mouse events

[Ivan S. Lyapunov]

Hello.

I'm write a small program and i want to make frameless parent window with
mouse dragging enabled
This code has a bug on Windows XP (and m.b anywhere else)
when system panel with Start menu button is placed on left or on top of the
desktop
qwidget::mouseMoveEvent receives incorrect coordinates, so the dragging
window jump to the width()/heith() of the system Start menu panel.
The manual drag works if Qt::Popup style is enabled to widget but it is not
a correct style for use.

I'm using qt 4.5 rc1, compiled this Visual Studio 2005 SP1
the sample of the problem code is attached

// QMoveError.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <QtGui/QApplication>

#include <QtGui/QWidget>
#include <QtGui/QDesktopWidget>

#include "QErrWidget.h"

int _tmain(int argc, char* argv[])
{
    QApplication app(argc, argv);
    QApplication::desktop()->availableGeometry();

    QWidget *q = new QErrWidget;
    q->show();
    return app.exec();
}

// QErrWidget.h
//

#include <QtGui/QWidget>

#ifndef QERRWIDGET_H
#define QERRWIDGET_H

class QErrWidget :    public QWidget
{
private:
    int _dx, _dy;
    bool m_drag;

protected:
    virtual void mouseMoveEvent(QMouseEvent *event);
    virtual void mousePressEvent(QMouseEvent *event);
    virtual void mouseReleaseEvent(QMouseEvent *event);

public:
    QErrWidget(void);
    virtual ~QErrWidget(void);
};



#endif

// QErrWidget.cpp

#include "QErrWidget.h"

#include <QtGui/QApplication>
#include <QtGui/QWidget>
#include <QtGui/QDesktopWidget>
#include <QtGui/QMouseEvent>

QErrWidget::QErrWidget(void)
: QWidget(0, Qt::Window | Qt::WindowMinimizeButtonHint |
Qt::WindowSystemMenuHint | Qt::FramelessWindowHint),
    _dx(-1), _dy(-1), m_drag(false)
{
    resize(320, 240);
    move((QApplication::desktop()->size().width() - width()) / 2,
(QApplication::desktop()->size().height() - height()) / 2);
}

QErrWidget::~QErrWidget(void)
{
}

void QErrWidget::mousePressEvent(QMouseEvent *event)
{
    // drag window operations here
    if (!m_drag && Qt::LeftButton == event->button()) {
        _dx = event->x();
        _dy = event->y();
        m_drag = true;
    }
}

void QErrWidget::mouseReleaseEvent(QMouseEvent *event)
{
    // drag window operations here
    m_drag = false;
}

void QErrWidget::mouseMoveEvent(QMouseEvent *event)
{
    // drag window operations here
    if (m_drag) {
        const int dx = event->x() - _dx;
        const int dy = event->y() - _dy;
        move(this->x() + dx, this->y() + dy);
    }
}
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