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Thread: QGraphicsItem paint problem

  1. #1
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    Default QGraphicsItem paint problem

    Hello,

    I have following files

    architem.h
    =========

    Qt Code:
    1. #ifndef ARCITEM_H
    2. #define ARCITEM_H
    3.  
    4. #include <QtWidgets>
    5.  
    6. class ArcItem : public QGraphicsItem
    7. {
    8. public:
    9. ArcItem(QGraphicsItem *parent=0);
    10. ~ArcItem();
    11.  
    12. QRectF boundingRect() const;
    13. void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    14. void setRect(QRectF rct);
    15.  
    16. protected:
    17. QVariant itemChange(GraphicsItemChange change, const QVariant &value);
    18.  
    19. private:
    20. QRectF arcRect;
    21. int startAngle;
    22. int spanAngle;
    23.  
    24. };
    25.  
    26. #endif // ARCITEM_H
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    arcitem.cpp
    =========

    Qt Code:
    1. #include "arcitem.h"
    2.  
    3. ArcItem::ArcItem(QGraphicsItem *parent): QGraphicsItem(parent),
    4. arcRect(0,0,100,100),
    5. startAngle(1*16),
    6. spanAngle(200*16)
    7. {
    8. setFlags(ItemIsSelectable|ItemIsMovable|ItemSendsGeometryChanges);
    9. setData(0,"ArcItem");
    10. }
    11.  
    12. ArcItem::~ArcItem()
    13. {
    14.  
    15. }
    16.  
    17. QVariant ArcItem::itemChange(GraphicsItemChange change, const QVariant &value)
    18. {
    19. return QGraphicsItem::itemChange(change, value);
    20. }
    21.  
    22.  
    23.  
    24. QRectF ArcItem::boundingRect() const
    25. {
    26. return arcRect;
    27. }
    28.  
    29. void ArcItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    30. {
    31. Q_UNUSED(option)
    32. Q_UNUSED(widget)
    33. painter->save();
    34. painter->drawArc(arcRect,startAngle,spanAngle);
    35. painter->restore();
    36. }
    37.  
    38. void ArcItem::setRect(QRectF rct)
    39. {
    40. arcRect = rct;
    41. update(rct);
    42. }
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    When I am resizing this item using handles, it show uncleared lines on scene as the picture attached.
    Actually, boundingrect is set from outside of this class by calling setRect custom method in this class.
    Although item gets resized, it behaves as per attachment.
    Any help on this?


    Thanks

    Manish
    Attached Images Attached Images

  2. #2
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    Default Re: QGraphicsItem paint problem

    The new rect is not necessarly encompassing the old rect, right?

    So calling update with just the new rect might leave area unupdated that was part of the previous rect.

    Maybe call update with the union of the old and the new rect?

    Cheers,
    _

  3. #3
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    Default Re: QGraphicsItem paint problem

    Thanks Anda.
    I did that as well but still the problem persists. I have infact updated bigger viewport as well.

  4. #4
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    Default Re: QGraphicsItem paint problem

    Is your item the only item showing that problem?

    Have you tried without the ItemSendsGeometryChanges flag?

    Cheers,
    _

  5. #5
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    Default Re: QGraphicsItem paint problem

    I don't see you calling prepareGeometryChange() after the bounding rect is changed.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  6. #6
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    Default Re: QGraphicsItem paint problem

    Thanks Wysota.
    Yes, prepareGeometryChange() has made the trick. Now it is working well and the problem is solved.


    Thanks

    Manish

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