Problem while removing QGraphicsPathItem from Scene after move.

Himanshu Rohilla

Hi everyone....

I am doing free hand drawing on QGraphicsView and QGraphicsScene. Following is my code:-

@WhiteBoardView::WhiteBoardView()
{
mDrawnPathItem = mWhiteBoardScene->addPath(QPainterPath());
mDrawnPathItem->setBrush( QColor(...) );
mDrawnPathItem->setPen(Qt::NoPen);
}

void WhiteBoardView::drawLineTo(const QPointF &previous, const QPointF &current, const QPen& drawPen)
{
QGraphicsLineItem lineHelper;
lineHelper.setLine( QLineF(previous, current) );
lineHelper.setPen(drawPen);

QPainterPath path = mDrawnPathItem->path();
    path.setFillRule(Qt::WindingFill);
    path.addPath( lineHelper.shape() );
path = path.simplified();

mDrawnPathItem->setPath(path);

m_DrawnItems << mDrawnPathItem;@

//mDrawnPathItem is of type QGraphicsPathItem* and was added in the constructor with an empty QPainterPath() and m_DrawnItems is a list of QGraphicsPathItem* .

Following code is to erase drawn line from scene :-

@void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

    //m_DrawnItems = QList<QGraphicsPathItem*>
    foreach( QGraphicsPathItem* item, m_DrawnItems)
    {
        QPainterPath drawnPath = item->path();
              drawnPath.subtracted(eraserPath)
        item->setPath(drawnPath);
    }
}@

I am doing drawing easily and removing drawn lines easily. But, If i move drawn line on scene and then remove or erase that moved line, it does not erase. I think, i am not getting the updated points of path.

Thanks in advance.... :)

raven-worx

how do you move the items exactly?

just a guess from me:
@
void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

        //m_DrawnItems = QList<QGraphicsPathItem*>
        foreach( QGraphicsPathItem* item, m_DrawnItems)
        {
            QPainterPath drawnPath = item->path();
                  drawnPath.subtracted(eraserPath.translated(item->pos()))
            item->setPath(drawnPath);
        }
    }

@

Himanshu Rohilla

Thanks to reply Raven.. Sorry but i am not moving like this. Following is my code to move:-

@
void WhiteBoardView::mousePressEvent (QMouseEvent *event)
{
previousPt = event->pos(); // previousPt is QPoint

vbMousePressed = true;   // vbMousePressed is bool type variable

if(event->button() == Qt::LeftButton)
{
       itemUnderMouse = this->itemAt(event->pos());   // itemUnderMouse is QGraphicsItem*
}

}

void WhiteBoardView::mouseMoveEvent (QMouseEvent *event)
{
vbMouseMoving = true;

if(event)
{
    if(vbMousePressed && vbMouseMoving)
    {
            if(itemUnderMouse == NULL)
            {
                return;
            }
            else
            {
                moveSelectedImg(event->pos());
            }

}
}
}

// Following function is used to move polygon.

void WhiteBoardView::moveSelectedImg(const QPoint &currnt)
{
if(currnt == previousPt || itemUnderMouse == NULL)
return;

int nXCor = currnt.x() - previousPt.x();
int nYCor = currnt.y() - previousPt.y();
itemUnderMouse->moveBy(nXCor, nYCor);

previousPt = currnt;

}

@

raven-worx

well...are you sure!?
check the "docs":http://qt-project.org/doc/qt-4.8/qgraphicsitem.html#moveBy and try my code pls.

Himanshu Rohilla

I could not move the QGraphicsPathItem according to your following code.

@void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

        //m_DrawnItems = QList<QGraphicsPathItem*>
        foreach( QGraphicsPathItem* item, m_DrawnItems)
        {
            QPainterPath drawnPath = item->path();
                  drawnPath.subtracted(eraserPath.translated(item->pos()))
            item->setPath(drawnPath);
        }
    }@

Himanshu Rohilla

Actually, i am moving the drawn QGraphicsPathItem over the QGraphicsView. This works fine. After moving, when i use eraser and move eraser over the new position of QGraphicsPathItem, it does not remove it but if i move eraser over its(QGraphicsPathItem's) last position, then it removes.

Himanshu Rohilla

I have checked that i am not able to find updated path of QGraphicsPathItem after using moveBy() function and also not able to store updated path in m_DrawnItems list.

raven-worx

try this:
@
drawnPath.subtracted(eraserPath.translated(-item->pos()))
@

or maybe it's easier to you if you dont move the item itself but only it's containing painterpath? Then there should also no changes be necessary in your eraser code.

@
void WhiteBoardView::moveSelectedImg(const QPoint &currnt)
{
if(currnt == previousPt || itemUnderMouse == NULL)
return;

int nXCor = currnt.x() - previousPt.x();
int nYCor = currnt.y() - previousPt.y();
QPainterPath path = ....; // get painter path from itemUnderMouse
    path.translate(nXCor, nXCor);
...  //set path back to item

previousPt = currnt;

}
@

Himanshu Rohilla

Ok.... But tell me that, should i use the following function with your suggestion ???

@/ Following function is used to move polygon.

void WhiteBoardView::moveSelectedImg(const QPoint &currnt)
{
if(currnt == previousPt || itemUnderMouse == NULL)
return;

int nXCor = currnt.x() - previousPt.x();
int nYCor = currnt.y() - previousPt.y();
itemUnderMouse->moveBy(nXCor, nYCor);

previousPt = currnt;

}@

Himanshu Rohilla

Sry, but it also does not work .... :(

Himanshu Rohilla

Raven, actually i forgot to tell you the code which execute on mouseRelease(). Sorry for this. Following code will execute on mouseRelease:-

@allItemsList = this->scene()->items();

                    qDebug() << "size of AllItemList" << allItemsList.size();

                    if(this->scene() != NULL)
                    {
                        this->setScene(mController->newSceneForView());   // It sets the new scene after translation of QGraphicsPathItems.

                        this->setSceneRect(qApp->desktop()->rect());

                        setGraphicsPathItem(this->scene());   // It sets QGraphicsPathItems for new Scene.

                        mController->updateBackground();   // It sets the white background.

                        for(int i=0; i<allItemsList.size(); i++)
                        {
                            QGraphicsItem* item = allItemsList[i];

                            if(mSelectedPolygonItem == qgraphicsitem_cast<QGraphicsPathItem*>(item))
                            {
                                this->scene()->addItem(item);

                                if(m_DrawnItems.contains(mSelectedPolygonItem))
                                {
                                    for(int i=0; i<m_DrawnItems.size(); i++)
                                    {
                                        if(m_DrawnItems[i] == mSelectedPolygonItem)
                                        {
                                            m_DrawnItems[i]->setPath(returnedPath);
                                        }
                                    }
                                }
                            }
                            else
                            {
                                this->scene()->addItem(item);
                            }
                        }
                    }

                    allItemsList.clear();@

smudibh20

Hey I want to do similar operation of moving a QGraphicsPathItem.
But I want to detect the movement, get the current coordinates of mouse pointer and redraw the path contained in that Item according to current coordinates.
How to do that?