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Thread: QGraphicsItem paint not triggered

  1. #1
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    Default QGraphicsItem paint not triggered

    If I add my subclassed QGraphicsItem before I add anything else to the scene everything works fine. But if I add something else before then the paint method is never triggered in my new QGraphicsItem. Can somebody explain what I am missing?


    Qt Code:
    1. MyScene::MyScene(QObject *parent)
    2. : QGraphicsScene(parent), currentDrawItem(NULL), bDraw(false)
    3. {
    4. void MyScene::toggleSymbols()
    5. {
    6. if(bSymbols)
    7. {
    8. qDebug("false");
    9. bSymbols = false;
    10. }
    11. else
    12. {
    13. qDebug("true");
    14. bSymbols = true;
    15. symbols = new itemSymbols(); //Subclassed QGraphicsItem
    16. QPointF centerPos = QPointF(this->sceneRect().width()/2, this->sceneRect().height()/2);
    17. symbols->setCenterPos(centerPos);
    18. addItem(symbols);
    19. }
    20. }
    21. }
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    Qt Code:
    1. itemSymbols::itemSymbols() : QGraphicsItem()
    2. {
    3. void itemSymbols::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    4. {
    5. Debug("itemSymbols paint()");
    6. }
    7. }
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  2. #2
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    Default Re: QGraphicsItem paint not triggered

    How did you implement boundingRect() for the item?
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  3. #3
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    Default Re: QGraphicsItem paint not triggered

    I've modified the code a bit know but still the same result.

    In MyScene.cpp I create the Item and set it´s size like this
    Qt Code:
    1. symbols = new itemSymbols();
    2. QSizeF size(this->sceneRect().width()*0.05,this->sceneRect().height()*0.07);
    3. QPointF centerPos = QPointF(this->sceneRect().center());
    4. symbols->setSize(centerPos, size);
    5. addItem(symbols);
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    And then in the item itself I do this

    Qt Code:
    1. void itemSymbols::setSize(QPointF pos, QSizeF size)
    2. {
    3. QRectF test(pos size);
    4. bBox = test;
    5. }
    6. QRectF itemSymbols::boundingRect() const
    7. {
    8. return bBox;
    9. }
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  4. #4
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    Default Re: QGraphicsItem paint not triggered

    No, this is wrong. If you modify the boundingRect value, you need to inform Graphics View about it by calling QGraphicsItem::prepareGeometryChange().
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  5. #5
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    Default Re: QGraphicsItem paint not triggered

    Oh ok. Like this?

    Qt Code:
    1. void itemSymbols::setSize(QPointF pos, QSizeF size)
    2. {
    3. centerPos = pos;
    4. QRectF test(centerPos,size);
    5. QGraphicsItem::prepareGeometryChange();
    6. bBox = test;
    7. }
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  6. #6
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    Default Re: QGraphicsItem paint not triggered

    Swap #5 and #6, just in case. And of course make sure you paint within the rectangle returned by boundingRect.
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  7. #7
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    Default Re: QGraphicsItem paint not triggered

    Ok thanks alot wysota. It still isn't working but now the paint method is triggered so hopefully it's not that hard no solve.

  8. #8
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    Default Re: QGraphicsItem paint not triggered

    What isn't working? From what I see you're not painting anything. Furthermore it seems your item should probably be derived from QGraphicsRectItem instead of QGraphicsItem.
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  9. #9
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    Default Re: QGraphicsItem paint not triggered

    This is my paint method. What I'm really trying to do here is a movable legend. As you can see the pen size is way off but any less than 200 is not visible so my guess is that I've mixed up the maybe the scene's coordinatesystem with the item's?

    Qt Code:
    1. void itemSymbols::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    2. {
    3. painter->setRenderHint(QPainter::Antialiasing);
    4. qDebug("itemSymbols paint()");
    5.  
    6. bBox.setHeight(height);
    7. bBox.setWidth(width);
    8.  
    9. QPointF header;
    10. header.setX(width/2);
    11. header.setY(height*0.05);
    12.  
    13. qreal newHeight = header.y();
    14.  
    15. QFont font;
    16. font.setBold(true);
    17. painter->setFont(font);
    18.  
    19. QPen pen;
    20. pen.setWidth(200);
    21. painter->setPen(pen);
    22.  
    23. painter->drawText(header,"Symbols");
    24.  
    25. qreal iRows = (height-newHeight)/15;
    26. qreal h = iRows;
    27.  
    28. qreal iCol = width/4;
    29. qreal c = iCol;
    30.  
    31. font.setBold(false);
    32. painter->setFont(font);
    33.  
    34. QFont font2;
    35. font2.setPointSizeF(4);
    36. painter->setFont(font2);
    37.  
    38. for(int i = 0;i<vPics.size();i++)
    39. {
    40. p.setX(10.0);
    41. p.setY(h+10);
    42.  
    43. QPointF p2;
    44. p2.setX(60.0);
    45. p2.setY(h);
    46.  
    47. h = h + iRows;
    48. c = c + iCol;
    49.  
    50. QPixmap pixmap(vPics.at(i));
    51. QRectF d = QRectF(p.x(),p.y(),28,28);
    52. //painter->drawRect(d);
    53. //painter->drawPixmap(p,pixmap);
    54.  
    55. const char *chTemp;
    56. chTemp = vDesc.at(i).toAscii();
    57. QRectF t = QRectF(p2.x(), p.y(),120,30);
    58. //painter->drawRect(t);
    59. //painter->drawText(QRectF(p2.x(), p.y(),120,30), Qt::AlignCenter, QObject::tr(chTemp));
    60. }
    61.  
    62. qDebug("Drawing a box at pos %f %f", bBox.topLeft().x(), bBox.topLeft().y());
    63. painter->drawRect(bBox);
    64. painter->drawPoint(centerPos);
    65. }
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  10. #10
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    Default Re: QGraphicsItem paint not triggered

    I don't know what width and height are but changing the bounding box in the paint routine is definitely a bad idea. The method is called paint() and not paintAndUpdateBoundingBox(). Not knowing the scene size and the transformation matrix of the view I'm unable to say anything about the pen size.
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