Painting problem for QGraphicsItem

[vivekpurohit]

I have to draw polygons on a scene. The polygon coordinates (in meters) are defined in a file like this:

POLYGON LAYER 3
21510.021 -77875.788 21767.976 -78175.582 22040.392 -78262.410
22762.365 -78488.670 23023.361 -78840.834 23401.474 -78810.424
23574.386 -78526.898 23190.596 -78121.994 22981.393 -77899.388
22236.109 -77426.189 21510.021 -77875.788

A Polygon resides in layers which can be any from 1 to 10.

I create Layers which are QGraphicsItem and add them to scene using scene.additem().
Then i create Polygons which are also QGraphicsItem and set the corresponding layer as its parent item.

Code Polygon.cpp:

Polygon::Polygon(QList<QPointF> *polygonPointList, qreal minX, qreal maxX, qreal minY, qreal maxY, QColor color)
{
    _pen = new QPen();
    _pen->setColor(color);
    _rectWidth = maxX-minX;
    _rectHeight = maxY-minY;
    _rectX = -(_rectWidth)/2.0;
    _rectY = -(_rectHeight)/2.0; 
 
    _polygonPath = new QPainterPath();
    _polygonPath->moveTo(polygonPointList->takeAt(0));
 
    while(!polygonPointList->isEmpty()){
        _polygonPath->lineTo(polygonPointList->takeAt(0));
    }
}
 
QRectF Polygon::boundingRect() const
{
    qreal adjustment = 2.000;
    return QRectF(_rectX-adjustment,_rectY-adjustment,_rectWidth+2*adjustment,_rectHeight+2*adjustment);
}
 
void Polygon::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->setPen(*_pen);
    painter->drawPath(*_polygonPath);
    return;
}

Polygon::Polygon(QList<QPointF> *polygonPointList, qreal minX, qreal maxX, qreal minY, qreal maxY, QColor color)
{
    _pen = new QPen();
    _pen->setColor(color);
    _rectWidth = maxX-minX;
    _rectHeight = maxY-minY;
    _rectX = -(_rectWidth)/2.0;
    _rectY = -(_rectHeight)/2.0; 

    _polygonPath = new QPainterPath();
    _polygonPath->moveTo(polygonPointList->takeAt(0));
    
    while(!polygonPointList->isEmpty()){
        _polygonPath->lineTo(polygonPointList->takeAt(0));
    }
}

QRectF Polygon::boundingRect() const
{
    qreal adjustment = 2.000;
    return QRectF(_rectX-adjustment,_rectY-adjustment,_rectWidth+2*adjustment,_rectHeight+2*adjustment);
}

void Polygon::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->setPen(*_pen);
    painter->drawPath(*_polygonPath);
    return;
}

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Problem:
The polygons get painted on the scene but when I scroll the view they don't get repainted correctly.I think
this may be due to incorrect boundingRects. What is the problem with the code above??

[MarekR22]

Why reinvent the weel? Just use QGraphicsPolygonItem.