QGraphicsLineItem :: paint () artifacts

I have my own class that inherits from QGraphicsLineItem

and overrides the method paint()

for drawing a thick line with an arrow:

void MyGraphicsItem::paint( QPainter* aPainter,
                            const QStyleOptionGraphicsItem* aOption,
                            QWidget* aWidget /*= nullptr*/ )
{
    Q_UNUSED( aOption );
    Q_UNUSED( aWidget );

    QLineF cLine = line();

    aPainter->setPen( QPen( Qt::black, 6, Qt::SolidLine ) );
    aPainter->drawLine( cLine );

    qreal lineAngle = cLine.angle();

    const qreal radius = 2.0;
    QLineF head1 = cLine;
    head1.setAngle(lineAngle+32);
    head1.setLength( 12 );
    QLineF head2 = cLine;
    head2.setAngle(lineAngle-32);
    head2.setLength( 12 );

    aPainter->drawLine( head1 );
    aPainter->drawLine( head2 );

    aPainter->setPen( QPen( Qt::yellow, 2, Qt::SolidLine ) );

    aPainter->drawLine( cLine );

    aPainter->drawLine( head1 );
    aPainter->drawLine( head2 );
}

      

        
        
        
      

    

This seems to be causing the artifacts to render when I draw an element around the scene. From what I can tell, because I set the thickness to QPen

, what leads me to believe that I should somehow draw outside of the elements rectangle?

What is causing my rendering problem and how can I solve it?

Note that the background is not redrawn on the image - this happens with any other objects in the scene that are also dragged by the arrow.

Edit: I think this is actually my problem:

Subclassing QGraphicsView and setting drawBackground

Edit again: The issue seems to be background related, but using full blown updates port updates kill performance, so I came up with this, which seems to increase CPU usage by 3% rather than binding one core to 100% use.

// This code lives in the QGraphicsScene constructor, doesn't have to be there though since QGraphicsScene::setBackgroundBrush is public.
int gridSizeX = 25;
int gridSizeY = 20;
QImage singleGrid( gridSizeX, gridSizeY, QImage::Format_RGB32 );
singleGrid.fill( Qt::white );
{
    QPainter painter( &singleGrid );

    // Lighter background
    painter.setPen( QPen( QColor( 240, 240, 240 ) ));

    qreal midx = gridSizeX / 2;
    qreal midy = gridSizeY / 2;
    painter.drawLine( 0, midy, gridSizeX, midy );
    painter.drawLine( midx, 0, midx, gridSizeY );

    // Darker foregound
    painter.setPen( QPen( QColor( 180, 180, 180 ) ));
    painter.drawRect( 0, 0, gridSizeX, gridSizeY );

    painter.end();
}
QBrush brushBackground( singleGrid );
setBackgroundBrush( brushBackground );

      

        
        
        
      

    

The scene then repeats that brush throughout, resulting in the same mesh background effect that even works when scaling / scaling.:.)