Drawing a selection rectangle

[Caius Aérobus]

Hello,
I would like to start a selection process as a MousePressEvent is detected and define the definitive selection area as a MouseReleaseEvent is detected.
But I would like to draw the selection area as teh user is still moving the mouse with the left button pushed.
My problem is that I would like a paint event be processed immediatly after any MouseMoveEvent was detected, and then draw both the old and the new selection using Xor mode.
So 2 questions:
- is this the right way to make it?
- if yes how could I force processing a paint event afer every MouseMoveEvent (of course QCoreApplication:rocessEvents() does not work in a MouseMoveEvent)
Thanks in advance for your help.

[talk2amulya]

i m not sure, but would this work for you?

YourWidget::mousePressEvent(QMouseEvent *e)
{
    point1 = e->globalPos();//get global position according to ur parent-child relationship
}
 
YourWidget::mouseReleaseEvent(QMouseEvent *e)
{
    point2 = e->globalPos();//get global position according to ur parent-child relationship
    QPainter painter(this);
    painter->drawRect(point1, point2);
}

YourWidget::mousePressEvent(QMouseEvent *e)
{
    point1 = e->globalPos();//get global position according to ur parent-child relationship
}

YourWidget::mouseReleaseEvent(QMouseEvent *e)
{
    point2 = e->globalPos();//get global position according to ur parent-child relationship
    QPainter painter(this);
    painter->drawRect(point1, point2);
}

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[Caius Aérobus]

i m not sure, but would this work for you?

YourWidget::mousePressEvent(QMouseEvent *e)
{
    point1 = e->globalPos();//get global position according to ur parent-child relationship
}
 
YourWidget::mouseReleaseEvent(QMouseEvent *e)
{
    point2 = e->globalPos();//get global position according to ur parent-child relationship
    QPainter painter(this);
    painter->drawRect(point1, point2);
}

YourWidget::mousePressEvent(QMouseEvent *e)
{
    point1 = e->globalPos();//get global position according to ur parent-child relationship
}

YourWidget::mouseReleaseEvent(QMouseEvent *e)
{
    point2 = e->globalPos();//get global position according to ur parent-child relationship
    QPainter painter(this);
    painter->drawRect(point1, point2);
}

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Hmmmm, I believed paintings should only occur in a paintEvent...

[talk2amulya]

QPainter's common use is there, that doesnt mean u cant use it elsewhere i dont know if its the most optimized way of doing it, just felt like the right way and done on the fly, so bear with me

[aamer4yu]

Drawing in the mouse events wont be a good idea.
Reason : the next paint event call will erase it !

For your need, have a look at QRubberBand class. Fits very well to ur needs

[talk2amulya]

hey caius,

sorry abt a wrong and hasty post..i didnt really think about it

[zarkzervo]

I have this in my inherited GraphicsScene:

void MyGraphicsScene::mousePressEvent ( QGraphicsSceneMouseEvent * event )
{
  event->ignore();
 
  // Reset selectionArea
  setSelectionArea(QPainterPath());
 
  // Always remember to call parents mousePressEvent
  QGraphicsScene::mousePressEvent(event);
}

void MyGraphicsScene::mousePressEvent ( QGraphicsSceneMouseEvent * event )
{
  event->ignore();

  // Reset selectionArea
  setSelectionArea(QPainterPath());

  // Always remember to call parents mousePressEvent
  QGraphicsScene::mousePressEvent(event);
}

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and

void MyGraphicsScene::mouseReleaseEvent ( QGraphicsSceneMouseEvent * event )
{
  event->ignore();
 
  bool ctrl = (event->modifiers() == Qt::ControlModifier);
 
  QPainterPath tmpPath = selectionArea();
  if(tmpPath.isEmpty())
  {
    // if ctrl pressed, then toggle selection
    emit select(event->scenePos(), ctrl);
  }
  else
  {
    // if ctrl pressed, then add selection
    emit select(tmpPath, ctrl);
  }
 
  // Always remember to call parents mousePressEvent
  QGraphicsScene::mouseReleaseEvent(event);
 
}

void MyGraphicsScene::mouseReleaseEvent ( QGraphicsSceneMouseEvent * event )
{
  event->ignore();

  bool ctrl = (event->modifiers() == Qt::ControlModifier);

  QPainterPath tmpPath = selectionArea();
  if(tmpPath.isEmpty())
  {
    // if ctrl pressed, then toggle selection
    emit select(event->scenePos(), ctrl);
  }
  else
  {
    // if ctrl pressed, then add selection
    emit select(tmpPath, ctrl);
  }

  // Always remember to call parents mousePressEvent
  QGraphicsScene::mouseReleaseEvent(event);

}

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I just inherited QGraphicsScene locally just to re-implement these two functions. This is the complete code I use in these two functions. You may not need all, but what I do, is to emit the signal with the path (selection rectangle) and if the user has pressed ctrl (adding elements)

Hope this helps and I didn't misunderstand your question.

[Caius Aérobus]

Hope this helps and I didn't misunderstand your question.

You didn't but since I do not use QGraphicsScene...