Not Scaling QBrush style fro qgraphics view item

**dan** · 3rd June 2008, 03:35

Hi,

Thanks for you help but I cannot get your suggestion to work properly.
I overloaded the paint method for a class derived from qgraphicsitem as you showed but this does not work for me. It seems that the brush pattern matrix does not have any effect at all.

For example:

Qt Code:

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void Node::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
   QBrush myBrush(Qt::red, Qt::DiagCrossPattern);
   QMatrix myMatrix(99,0,99,0,0,0); 
   myBrush.setMatrix(myMatrix);
   painter->setBrush(myBrush);
   painter->drawEllipse(-50, -50, 100, 100);
}

void Node::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
   QBrush myBrush(Qt::red, Qt::DiagCrossPattern);
   QMatrix myMatrix(99,0,99,0,0,0); 
   myBrush.setMatrix(myMatrix);
   painter->setBrush(myBrush);
   painter->drawEllipse(-50, -50, 100, 100);
}

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produces a shape the looks the same as:

Qt Code:

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void Node::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
   QBrush myBrush(Qt::red, Qt::DiagCrossPattern);
   QMatrix myMatrix(1,0,1,0,0,0);  //don't scale this time
   myBrush.setMatrix(myMatrix);
   painter->setBrush(myBrush);
   painter->drawEllipse(-50, -50, 100, 100);
}

void Node::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
   QBrush myBrush(Qt::red, Qt::DiagCrossPattern);
   QMatrix myMatrix(1,0,1,0,0,0);  //don't scale this time
   myBrush.setMatrix(myMatrix);
   painter->setBrush(myBrush);
   painter->drawEllipse(-50, -50, 100, 100);
}

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I am using QT4.3.
Am I doing anything wrong here?
I've tried both the Qt:DiagCrossPattern brush and also a custom brush made with a QImage.

Thanks!

**Brandybuck** · 3rd June 2008, 17:08

Don't create your own matrix, use the one passed in option. That is the matrix the view uses. By taking the inverse matrix, you scale back down.

**dan** · 3rd June 2008, 20:05

Hi,

Yes, I understand your solution but it does not work for me. I have traced the problem to the fact that brush transforms don't seem to work at all. That's what I was demonstrating in the previous code. Apparently this was a bug that was fixed in 4.3.1 (http://trolltech.com/developer/task-...ntry&id=129520).

I was using 4.3.4 and am now downloading 4.4.0. Has anybody else used a qBrush transform? What version were you using? Am I not doing something proper?

Thanks,
Dan