Detecting and reacting to mouse dragging in QGraphicsView?

[swbluto]

Ok, so I'm trying to do things with the MousePress, MouseRelease and MouseMove events and they all seem to work as far as they seem like they're literally supposed to work, but I use a custom boolean "mouseDown" to detect if the mouse is down and realized I need to process code whenever the mouse is down, whether moving or not. MousePress only triggers on a mouse press, MouseRelease only triggers when it's released, and MouseMove only triggers when the mouse is moved. How can I implement something that's triggered whenever the custom boolean "mouseDown" is true (or any condition is true for that matter)?

Ok, I never did implement the "execute whenever mousedown" is true, but I found another way around the problem I was having. When I move the mouse with the button down and then stopped, the "change x" variable of the image didn't go to zero (i.e. the image kept moving), so I needed to find a way to detect when the mouse stopped moving and that's what the mouseDown boolean was for.

However, I found that just by resetting the "change x" variable of the image to zero after advancing the image with "advance()" did what I wanted to. So no problems there.

Now, I need to make it "unchoppy" and the image seems to "slip" in regard to the mouse moving when I move "fast". I think I need advance() to trigger whenever the mouse is moved instead of on a fixed time interval... how would I do that? I'm thinking it has something to do with slots.

wait, would it be as simple as calling advance() inside the mouseMove event function? Can I even call advance() inside the QGraphicsScene class? *investigates*

Woah! I just found that I could call advance() directly inside the QGraphicsScene subclass and now it's truly dragging! Here's my code just in case some other n00b might benefit from it.

//#include <Q4MemArray>
//#include "canvas.h"
//#include <q4progressdialog.h>
//#include <Q4PointArray>
//#include <Q4PtrList>
//#include <QPixmap>
//#include "mapscene.h"
//#include <Q4PopupMenu>
 
#include <QApplication>
#include <QGraphicsEllipseItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QtGui>
 
#include <qdatetime.h>
#include <qmainwindow.h>
#include <qstatusbar.h>
#include <qmessagebox.h>
#include <qmenubar.h>
#include <qapplication.h>
#include <qpainter.h>
#include <qprinter.h>
#include <qlabel.h>
#include <qimage.h>
#include <qpixmap.h>
#include <QMouseEvent>
#include <QStyleOptionGraphicsItem>
#include <qdebug.h>
#include <stdlib.h>
#include <qtimer.h>
 
 
QString myImgName = "myimg.png";
static QImage *myImg;
 
        int xOffset;
        int yOffset;
 
  static const int imageRTTI = 984376;
 
void debug(QString s)
{
    qDebug(s.toAscii());
}
 
class mapScene: public QGraphicsScene
{
    public:
        mapScene();
 
        int mouseMoveX;
        int mouseMoveY;
        QPointF prevMousePoint;
        QPointF currMousePoint;
 
        bool mouseDown;
    protected:
        void mouseMoveEvent ( QGraphicsSceneMouseEvent * mouseEvent );
        void mousePressEvent ( QGraphicsSceneMouseEvent * mouseEvent );
        void mouseReleaseEvent ( QGraphicsSceneMouseEvent * mouseEvent );
 
};
 
mapScene::mapScene()
{
    mouseDown = false;
    mouseMoveX = 0;
    mouseMoveY = 0;
    xOffset =0;
    yOffset =0;
 
}
 
void mapScene::mouseMoveEvent( QGraphicsSceneMouseEvent * event)
{
    if(mouseDown)
    {
        QString dummy;
        debug("mommy");
        /*
        debug(dummy.setNum(event->pos().x()));
        debug(dummy.setNum(event->lastPos().x()));
        debug(dummy.setNum(event->lastScenePos().x()));
        debug(dummy.setNum(event->scenePos().x()));
        */
          xOffset = (int)(event->scenePos().x() - event->lastScenePos().x());
          yOffset = (int)(event->scenePos().y() - event->lastScenePos().y());
          advance();
    }
    else
    {
        xOffset = 0;
        yOffset = 0;
    }
}
 
void mapScene::mousePressEvent( QGraphicsSceneMouseEvent * event)
{
    mouseDown = true;
}
 
void mapScene::mouseReleaseEvent( QGraphicsSceneMouseEvent * event)
{
    mouseDown = false;
    xOffset = 0;
    yOffset = 0;
}
 
 
 
class ImageItem: public QGraphicsRectItem
{
public:
    ImageItem( QImage img );
    int rtti () const { return imageRTTI; }
    void advance(int phase);
protected:
    void paint( QPainter *, const QStyleOptionGraphicsItem *option, QWidget *widget );
private:
    QImage image;
    QPixmap pixmap;
    int state;
};
 
 
void ImageItem::advance(int phase)
{
 
        moveBy(xOffset,yOffset);
        xOffset = 0; yOffset = 0;
}
 
 
ImageItem::ImageItem( QImage img )
    : image(img)
{
    state = 0;
    setRect(0, 0, image.width(), image.height());
    setFlag(ItemIsMovable);
#if !defined(Q_WS_QWS)
    pixmap = pixmap.fromImage(image, Qt::OrderedAlphaDither);
#endif
}
 
void ImageItem::paint( QPainter *p, const QStyleOptionGraphicsItem *option, QWidget * )
{
// On Qt/Embedded, we can paint a QImage as fast as a QPixmap,
// but on other platforms, we need to use a QPixmap.
#if defined(Q_WS_QWS)
    p->drawImage( option->exposedRect, image, option->exposedRect, Qt::OrderedAlphaDither );
#else
    p->drawPixmap( option->exposedRect, pixmap, option->exposedRect );
#endif
}
 
int main( int argc, char **argv )
{
 
    QApplication app(argc, argv);
 
    mapScene scene;//mapScene scene;
    scene.setSceneRect( -500.0, -500.0, 1000.0, 1000.0 );//( -100.0, -100.0, 200.0, 200.0 );
 
    myImg = new QImage;
    myImg->load(myImgName);
 
 
    QAbstractGraphicsShapeItem* i = new ImageItem(*myImg);
    scene.addItem(i);
    i->setPos(-50,-50);
 
 
 
    QGraphicsView view( &scene );
   // view.setDragMode(QGraphicsView::ScrollHandDrag);
    view.setRenderHints( QPainter::Antialiasing );
    view.show();
 
    return app.exec();
}

//#include <Q4MemArray>
//#include "canvas.h"
//#include <q4progressdialog.h>
//#include <Q4PointArray>
//#include <Q4PtrList>
//#include <QPixmap>
//#include "mapscene.h"
//#include <Q4PopupMenu>

#include <QApplication>
#include <QGraphicsEllipseItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QtGui>

#include <qdatetime.h>
#include <qmainwindow.h>
#include <qstatusbar.h>
#include <qmessagebox.h>
#include <qmenubar.h>
#include <qapplication.h>
#include <qpainter.h>
#include <qprinter.h>
#include <qlabel.h>
#include <qimage.h>
#include <qpixmap.h>
#include <QMouseEvent>
#include <QStyleOptionGraphicsItem>
#include <qdebug.h>
#include <stdlib.h>
#include <qtimer.h>


QString myImgName = "myimg.png";
static QImage *myImg;

        int xOffset;
        int yOffset;

  static const int imageRTTI = 984376;

void debug(QString s)
{
    qDebug(s.toAscii());
}

class mapScene: public QGraphicsScene
{
    public:
        mapScene();

        int mouseMoveX;
        int mouseMoveY;
        QPointF prevMousePoint;
        QPointF currMousePoint;

        bool mouseDown;
    protected:
        void mouseMoveEvent ( QGraphicsSceneMouseEvent * mouseEvent );
        void mousePressEvent ( QGraphicsSceneMouseEvent * mouseEvent );
        void mouseReleaseEvent ( QGraphicsSceneMouseEvent * mouseEvent );

};

mapScene::mapScene()
{
    mouseDown = false;
    mouseMoveX = 0;
    mouseMoveY = 0;
    xOffset =0;
    yOffset =0;

}

void mapScene::mouseMoveEvent( QGraphicsSceneMouseEvent * event)
{
    if(mouseDown)
    {
        QString dummy;
        debug("mommy");
        /*
        debug(dummy.setNum(event->pos().x()));
        debug(dummy.setNum(event->lastPos().x()));
        debug(dummy.setNum(event->lastScenePos().x()));
        debug(dummy.setNum(event->scenePos().x()));
        */
          xOffset = (int)(event->scenePos().x() - event->lastScenePos().x());
          yOffset = (int)(event->scenePos().y() - event->lastScenePos().y());
          advance();
    }
    else
    {
        xOffset = 0;
        yOffset = 0;
    }
}

void mapScene::mousePressEvent( QGraphicsSceneMouseEvent * event)
{
    mouseDown = true;
}

void mapScene::mouseReleaseEvent( QGraphicsSceneMouseEvent * event)
{
    mouseDown = false;
    xOffset = 0;
    yOffset = 0;
}



class ImageItem: public QGraphicsRectItem
{
public:
    ImageItem( QImage img );
    int rtti () const { return imageRTTI; }
    void advance(int phase);
protected:
    void paint( QPainter *, const QStyleOptionGraphicsItem *option, QWidget *widget );
private:
    QImage image;
    QPixmap pixmap;
    int state;
};


void ImageItem::advance(int phase)
{

        moveBy(xOffset,yOffset);
        xOffset = 0; yOffset = 0;
}


ImageItem::ImageItem( QImage img )
    : image(img)
{
    state = 0;
    setRect(0, 0, image.width(), image.height());
    setFlag(ItemIsMovable);
#if !defined(Q_WS_QWS)
    pixmap = pixmap.fromImage(image, Qt::OrderedAlphaDither);
#endif
}

void ImageItem::paint( QPainter *p, const QStyleOptionGraphicsItem *option, QWidget * )
{
// On Qt/Embedded, we can paint a QImage as fast as a QPixmap,
// but on other platforms, we need to use a QPixmap.
#if defined(Q_WS_QWS)
    p->drawImage( option->exposedRect, image, option->exposedRect, Qt::OrderedAlphaDither );
#else
    p->drawPixmap( option->exposedRect, pixmap, option->exposedRect );
#endif
}

int main( int argc, char **argv )
{

    QApplication app(argc, argv);

    mapScene scene;//mapScene scene;
    scene.setSceneRect( -500.0, -500.0, 1000.0, 1000.0 );//( -100.0, -100.0, 200.0, 200.0 );

    myImg = new QImage;
    myImg->load(myImgName);


    QAbstractGraphicsShapeItem* i = new ImageItem(*myImg);
    scene.addItem(i);
    i->setPos(-50,-50);



    QGraphicsView view( &scene );
   // view.setDragMode(QGraphicsView::ScrollHandDrag);
    view.setRenderHints( QPainter::Antialiasing );
    view.show();

    return app.exec();
}

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I'm now trying to get this dragging behavior to work for multiple images all at the same time but only one image (coindentally, the first one that I added to the scene) moves, but if the first one goes off the screen, then the second one moves, albeit at a slower rate than the mouse moving meaning it's only getting triggered to move a part of the time the mouse is moved. It seems this is sufficiently different to deserve its own thread, so I'm posting that issue at http://www.qtcentre.org/forum/f-qt-p...ene-25083.html .