qgraphicsview cursor setting logic

[mcarter]

This widget is one of several components. I need the cursor to change just on the widget itself and not on the entire application so the override cursor is not an option.

So I took your suggestion and implemented a custom event (with the code below), but the event is processed before returning back to qgraphicsview and same issue happens :-(

I even added the ability to change the viewport cursor from the view context menu, and the same thing happens . . . the set cursor and the change cursor event are happening before the qv mouse move event and when it returns to the mouse event, it sets the cursor to the original "unwanted" cursor.

#ifndef __EVENT_H__
#define __EVENT_H__
 
#include <QEvent>
#include <QCursor>
 
class SetCursorEvent : public QEvent
{
public:
    SetCursorEvent( const QCursor & cursor )
     :  QEvent( SetCursorEvent::type() ),
        m_cursor( cursor )
    {}
 
    virtual ~SetCursorEvent()
    {}
 
    static QEvent::Type type()
    {
        return EventType;
    }
 
    QCursor cursor() const
    {
        return m_cursor;
    }
 
private:
    static QEvent::Type EventType;
    QCursor m_cursor;
};
 
#endif

#ifndef __EVENT_H__
#define __EVENT_H__

#include <QEvent>
#include <QCursor>

class SetCursorEvent : public QEvent
{
public:
    SetCursorEvent( const QCursor & cursor )
     :  QEvent( SetCursorEvent::type() ),
        m_cursor( cursor )
    {}

    virtual ~SetCursorEvent()
    {}

    static QEvent::Type type()
    {
        return EventType;
    }

    QCursor cursor() const
    {
        return m_cursor;
    }

private:
    static QEvent::Type EventType;
    QCursor m_cursor;
};

#endif

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#ifndef __VIEW_H__
#define __VIEW_H__
 
#include "event.h"
 
#include <QDebug>
#include <QEvent>
#include <QGraphicsView>
 
class View : public QGraphicsView
{
    Q_OBJECT
 
public:
    View( QWidget* parent = 0 ) : QGraphicsView( parent )
    {
        setFrameStyle( QFrame::NoFrame );
        setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
        setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
    }
 
protected:
    bool viewportEvent( QEvent * event )
    {
        if( QEvent::CursorChange == event->type() )
        {
            qDebug() << "Cursor Change:" << viewport()->cursor().shape();
        }
        else if( SetCursorEvent::type() == event->type() )
        {
            SetCursorEvent * e = static_cast<SetCursorEvent*>(event);
            qDebug() << "SetCursorEvent:" << e->cursor().shape();
            viewport()->setCursor( e->cursor() );
        }
        return QGraphicsView::viewportEvent(event);
    }
};
 
#endif

#ifndef __VIEW_H__
#define __VIEW_H__

#include "event.h"

#include <QDebug>
#include <QEvent>
#include <QGraphicsView>

class View : public QGraphicsView
{
    Q_OBJECT

public:
    View( QWidget* parent = 0 ) : QGraphicsView( parent )
    {
        setFrameStyle( QFrame::NoFrame );
        setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
        setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
    }

protected:
    bool viewportEvent( QEvent * event )
    {
        if( QEvent::CursorChange == event->type() )
        {
            qDebug() << "Cursor Change:" << viewport()->cursor().shape();
        }
        else if( SetCursorEvent::type() == event->type() )
        {
            SetCursorEvent * e = static_cast<SetCursorEvent*>(event);
            qDebug() << "SetCursorEvent:" << e->cursor().shape();
            viewport()->setCursor( e->cursor() );
        }
        return QGraphicsView::viewportEvent(event);
    }
};

#endif

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#include "event.h"
#include "window.h"
#include "view.h"
#include "item.h"
 
#include <QAction>
#include <QApplication>
#include <QGraphicsScene>
#include <QMenu>
 
QEvent::Type SetCursorEvent::EventType =
                    static_cast<QEvent::Type>(QEvent::registerEventType());
 
Window::Window( QWidget * p )
 :  QMainWindow( p )
{
    m_scene = new QGraphicsScene( 0, 0, 1000, 1000);
    m_scene->setBackgroundBrush(QBrush(Qt::black, Qt::SolidPattern));
 
    m_view = new View;
    m_view->setScene(m_scene);
    m_view->fitInView( m_scene->sceneRect() );
    setCentralWidget(m_view);
 
    m_view->setContextMenuPolicy( Qt::CustomContextMenu );
    connect( m_view,
                SIGNAL( customContextMenuRequested(const QPoint &) ),
                SLOT( viewContextMenu(const QPoint &) ) );
 
    m_view->viewport()->setCursor( Qt::CrossCursor );
}
 
Window::~Window()
{
}
 
void Window::viewContextMenu( const QPoint & pt )
{
    QMenu contextMenu;
    QAction * act;
 
    contextMenu.addAction( tr("Extract Item") );
    contextMenu.addAction( tr("Change Cursor") );
 
    act = contextMenu.exec( m_view->viewport()->mapToGlobal(pt) );
    if( NULL != act )
    {
        switch( contextMenu.actions().indexOf(act) )
        {
            case 0:
            {
                Item *item = new Item;
                item->setRect( QRectF( 0, 0, 100, 100 ) );
                item->setPen( QPen(Qt::green) );
                item->setBrush( QBrush(Qt::red) );
                item->setPos( m_view->mapToScene(pt) );
                item->setCursor( Qt::SizeAllCursor );
                item->setFlag( QGraphicsItem::ItemIsMovable, true );
                connect( item,
                    SIGNAL( requestContextMenu(const QPoint&,const QRectF&) ),
                    SLOT( extractContextMenu(const QPoint&,const QRectF&) ) );
                m_scene->addItem(item);
 
                m_view->setContextMenuPolicy( Qt::DefaultContextMenu );
                m_view->viewport()->setCursor( Qt::ForbiddenCursor );
                break;
            }
            case 1:
            {
                Qt::CursorShape shape;
                if( m_view->viewport()->cursor().shape() == Qt::OpenHandCursor )
                {
                    shape = Qt::CrossCursor;
                }
                else
                {
                    shape = Qt::OpenHandCursor;
                }
                SetCursorEvent * e = new SetCursorEvent( shape );
                QApplication::postEvent( m_view->viewport(), e );
                //m_view->viewport()->setCursor( shape );
                break;
            }
        }
    }
}
 
void Window::extractContextMenu( const QPoint & pt, const QRectF & /*rect*/ )
{
    QMenu contextMenu;
    QAction * act;
    Item *pGI = qobject_cast<Item*>(sender());
 
    contextMenu.addAction( tr("Done") );
    contextMenu.addAction( tr("Change Cursor") );
 
    act = contextMenu.exec( pt );
    if( NULL != act )
    {
        switch( contextMenu.actions().indexOf(act) )
        {
            case 0:
            {
                m_view->setContextMenuPolicy( Qt::CustomContextMenu );
                m_view->scene()->removeItem( pGI );
                delete pGI;
                //m_view->viewport()->setCursor( Qt::CrossCursor );
                SetCursorEvent * e = new SetCursorEvent( Qt::CrossCursor );
                QApplication::postEvent( m_view->viewport(), e );
                break;
            }
            case 1:
            {
                //m_view->viewport()->setCursor( Qt::WaitCursor );
                SetCursorEvent * e = new SetCursorEvent( Qt::WaitCursor );
                QApplication::postEvent( m_view->viewport(), e );
                break;
            }
        }
    }
}

#include "event.h"
#include "window.h"
#include "view.h"
#include "item.h"

#include <QAction>
#include <QApplication>
#include <QGraphicsScene>
#include <QMenu>

QEvent::Type SetCursorEvent::EventType =
                    static_cast<QEvent::Type>(QEvent::registerEventType());

Window::Window( QWidget * p )
 :  QMainWindow( p )
{
    m_scene = new QGraphicsScene( 0, 0, 1000, 1000);
    m_scene->setBackgroundBrush(QBrush(Qt::black, Qt::SolidPattern));

    m_view = new View;
    m_view->setScene(m_scene);
    m_view->fitInView( m_scene->sceneRect() );
    setCentralWidget(m_view);

    m_view->setContextMenuPolicy( Qt::CustomContextMenu );
    connect( m_view,
                SIGNAL( customContextMenuRequested(const QPoint &) ),
                SLOT( viewContextMenu(const QPoint &) ) );

    m_view->viewport()->setCursor( Qt::CrossCursor );
}

Window::~Window()
{
}

void Window::viewContextMenu( const QPoint & pt )
{
    QMenu contextMenu;
    QAction * act;

    contextMenu.addAction( tr("Extract Item") );
    contextMenu.addAction( tr("Change Cursor") );

    act = contextMenu.exec( m_view->viewport()->mapToGlobal(pt) );
    if( NULL != act )
    {
        switch( contextMenu.actions().indexOf(act) )
        {
            case 0:
            {
                Item *item = new Item;
                item->setRect( QRectF( 0, 0, 100, 100 ) );
                item->setPen( QPen(Qt::green) );
                item->setBrush( QBrush(Qt::red) );
                item->setPos( m_view->mapToScene(pt) );
                item->setCursor( Qt::SizeAllCursor );
                item->setFlag( QGraphicsItem::ItemIsMovable, true );
                connect( item,
                    SIGNAL( requestContextMenu(const QPoint&,const QRectF&) ),
                    SLOT( extractContextMenu(const QPoint&,const QRectF&) ) );
                m_scene->addItem(item);

                m_view->setContextMenuPolicy( Qt::DefaultContextMenu );
                m_view->viewport()->setCursor( Qt::ForbiddenCursor );
                break;
            }
            case 1:
            {
                Qt::CursorShape shape;
                if( m_view->viewport()->cursor().shape() == Qt::OpenHandCursor )
                {
                    shape = Qt::CrossCursor;
                }
                else
                {
                    shape = Qt::OpenHandCursor;
                }
                SetCursorEvent * e = new SetCursorEvent( shape );
                QApplication::postEvent( m_view->viewport(), e );
                //m_view->viewport()->setCursor( shape );
                break;
            }
        }
    }
}

void Window::extractContextMenu( const QPoint & pt, const QRectF & /*rect*/ )
{
    QMenu contextMenu;
    QAction * act;
    Item *pGI = qobject_cast<Item*>(sender());

    contextMenu.addAction( tr("Done") );
    contextMenu.addAction( tr("Change Cursor") );

    act = contextMenu.exec( pt );
    if( NULL != act )
    {
        switch( contextMenu.actions().indexOf(act) )
        {
            case 0:
            {
                m_view->setContextMenuPolicy( Qt::CustomContextMenu );
                m_view->scene()->removeItem( pGI );
                delete pGI;
                //m_view->viewport()->setCursor( Qt::CrossCursor );
                SetCursorEvent * e = new SetCursorEvent( Qt::CrossCursor );
                QApplication::postEvent( m_view->viewport(), e );
                break;
            }
            case 1:
            {
                //m_view->viewport()->setCursor( Qt::WaitCursor );
                SetCursorEvent * e = new SetCursorEvent( Qt::WaitCursor );
                QApplication::postEvent( m_view->viewport(), e );
                break;
            }
        }
    }
}

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[wysota]

In that case use a singleshot timer or QMetaObject::invokeMethod() to call the cursor change functionality with a small delay (e.g. 20ms). The delay will not be noticable to the user.

[mcarter]

With singleShot timer, I can get the delay but the single/slot does not allow any arguments, eg new cursorMask . . . but I can probably work around that.
With invokeMethod, I can call the needed method with the proper argument, but I do not see a way to specify a delay? Am I missing something? Or are you saying to just use a 20 ms sleep?

[wysota]

With singleShot timer, I can get the delay but the single/slot does not allow any arguments, eg new cursorMask . . . but I can probably work around that.
With invokeMethod, I can call the needed method with the proper argument, but I do not see a way to specify a delay? Am I missing something? Or are you saying to just use a 20 ms sleep?

No, no sleep(). You can store the "argument" in some member variable and then fetch it from there when the timer fires.

[mcarter]

Right, no sleep . . . was just thinking how to use the invokeMethod.

I implemented the singleShot timer, and while it works with my linux laptop, it does not seem to work on my windows test machine. The cursor changes, but once I move the mouse it reverts to the previous cursor again.

I did find QTBUG-3732 and QTBUG-4190 in the Qt bug reports, which both seem exactly related to what I am seeing. However, they are both closed (2009/2010). What is the best procedure to re-open these bugs, because it looks like an obvious logic problem with the cursor and graphicsview. My suggestion would be to get rid of the internal originalCursor and use the cursor of the GraphicsView, since that it not really used anywhere, for the cursor of the viewport. I guess in the meantime I need to abort what I am trying to accomplish or try to "fix" graphicsview with my oen code.

Also, when I was working in windows, I noticed that the cursors are really unusable with a view that is mostly black (especially CrossCursor) . . . the cursor just "disappears". Do I need to use a custom cursor to get the same feel as with linux and X11?