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Thread: Preventing font scale in QGraphicsItem

  1. #1
    Join Date
    Feb 2015
    Qt products
    Qt4 Qt5
    Unix/X11 Windows

    Question Preventing font scale in QGraphicsItem

    I am using QGraphicsTextItem to paint the text on the scene. Text is painted along the path (QGraphicsPathItem), wich is parent of my QGraphicsTextItem - so the text rotation is changed to be along the path element and is sticked to it while zooming the view. But the font size of QGraphicsTextItem is also changing while zooming the view - this is what I am trying to avoid. If I set QGraphicsItem::ItemIgnoresTransformations flag to the QGraphicsTextItem it stops rotating while it's parent (QGraphicsPathItem) does.


    I do understand that I have to re-implement QGraphicsTextItem::paint function, but I am stuck with the coordination system. Here is the code (Label class inherits public QGraphicsTextItem):

    Qt Code:
    1. void Label::paint( QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget )
    2. {
    3. // Store current position and rotation
    4. QPointF position = pos();
    5. qreal angle = rotation();
    7. // Store current transformation matrix
    8. QTransform transform = painter->worldTransform();
    10. // Reset painter transformation
    11. painter->setTransform( QTransform() );
    13. // Rotate painter to the stored angle
    14. painter->rotate( angle );
    16. // Draw the text
    17. painter->drawText( mapToScene( position ), toPlainText() );
    19. // Restore transformation matrix
    20. painter->setTransform( transform );
    21. }
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    The position (and rotation) of my text on the screen is unpredictable :( What am I doing wrong? Thank you very much in advance.

  2. #2
    Join Date
    Jan 2008
    Alameda, CA, USA
    Thanked 852 Times in 839 Posts
    Qt products

    Default Re: Preventing font scale in QGraphicsItem

    Try putting the QGraphicsTextItem inside of a QGraphicsRectItem. Set ItemIgnoresTranformations on the text, but not on the rectangle. Set the rectangle size to match the bounds of your path. Rotate and scale the rectangle, instead of the text.

    You can set the rectangle to have no pen and no brush, which will basically make it invisible.

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