QGraphicsView scroll problem or retained image on screen

[chinghungpan]

Please Help me!!! And sorry about my poor English.
I add QGraphicsRectItem in QGraphicsScene, and set very large SceneRect. QGraphicsView show scroller up.
When mouse press , move on QGraphicsScene, I will do QGraphicsRectItem->setRect() .
When mouse release will hide QGraphicsRectItem.
when I move mouse and scroller , some time mouse release will have some retained image on QGraphicsView

my code:

ggraphicsView::ggraphicsView(QWidget *parent):
    QGraphicsView(parent)
 
{
    m_qGraphicsScene = new QGraphicsScene;
    setScene(m_qGraphicsScene);
    //selection box
    m_pGRecItemSelectionBox=new QGraphicsRectItem();
    m_qGraphicsScene->addItem(m_pGRecItemSelectionBox);
    m_qGraphicsScene->setSceneRect(QRectF(0,0, 600,1000));
}
 
void ggraphicsView::mousePressEvent( QMouseEvent* event)
{
     m_ptStartPoint = mapToScene(event->pos());
     m_pGRecItemSelectionBox->setRect(QRectF(m_ptStartPoint, QSize()));
     m_pGRecItemSelectionBox->show();
}
 
void ggraphicsView::mouseMoveEvent (QMouseEvent* event)
{
    m_ptMovePoint = mapToScene(event->pos());
    m_pGRecItemSelectionBox->setRect(QRectF(m_ptStartPoint, m_ptMovePoint).normalized());
    m_pGRecItemSelectionBox->setBrush(QBrush(QColor(128, 128, 255, 100),Qt::SolidPattern));
    m_pGRecItemSelectionBox->setPen(QPen(Qt::NoPen));
 
}
void ggraphicsView::mouseReleaseEvent( QMouseEvent* event)
{
    m_pGRecItemSelectionBox->hide();
}

ggraphicsView::ggraphicsView(QWidget *parent):
    QGraphicsView(parent)

{
    m_qGraphicsScene = new QGraphicsScene;
    setScene(m_qGraphicsScene);
    //selection box
    m_pGRecItemSelectionBox=new QGraphicsRectItem();
    m_qGraphicsScene->addItem(m_pGRecItemSelectionBox);
    m_qGraphicsScene->setSceneRect(QRectF(0,0, 600,1000));
}

void ggraphicsView::mousePressEvent( QMouseEvent* event)
{
     m_ptStartPoint = mapToScene(event->pos());
     m_pGRecItemSelectionBox->setRect(QRectF(m_ptStartPoint, QSize()));
     m_pGRecItemSelectionBox->show();
}

void ggraphicsView::mouseMoveEvent (QMouseEvent* event)
{
    m_ptMovePoint = mapToScene(event->pos());
    m_pGRecItemSelectionBox->setRect(QRectF(m_ptStartPoint, m_ptMovePoint).normalized());
    m_pGRecItemSelectionBox->setBrush(QBrush(QColor(128, 128, 255, 100),Qt::SolidPattern));
    m_pGRecItemSelectionBox->setPen(QPen(Qt::NoPen));

}
void ggraphicsView::mouseReleaseEvent( QMouseEvent* event)
{
    m_pGRecItemSelectionBox->hide();
}

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problem: retained image ,when mouse move & wheel together.
未命名.png

[stampede]

I don't know what you are trying to do, but maybe try calling QGraphicsScene::update() at the end of move and release handlers.

[chinghungpan]

it is weird, i answer my question.
this quest I try to do QRubberBand.
mouse press and move show a Rectangle, mouse release will disappear.

It is about viewport update. if someone have same problem, u can see QGraphicsView::ViewportUpdateMode.

[wysota]

You always use some viewport update mode Maybe you disabled automatic updates.