PDA

View Full Version : Drawing a selection rectangle



Caius Aérobus
1st April 2009, 17:15
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::processEvents() does not work in a MouseMoveEvent)
Thanks in advance for your help.

talk2amulya
1st April 2009, 18:30
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);
}

Caius Aérobus
1st April 2009, 18:41
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);
}

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

talk2amulya
1st April 2009, 18:47
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
1st April 2009, 21:16
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
1st April 2009, 21:35
hey caius,

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

zarkzervo
2nd April 2009, 08:53
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);
}


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);

}

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
4th April 2009, 16:47
Hope this helps and I didn't misunderstand your question.

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