QBrush pattern problem

[ilovethisgame]

When window size is changed by using QPainter:: setWindow(...)
during a zooming process, the behaviour of brush pattern is very
wierd (please look at the attached bmp). Is there any way to make
the brush pattern stable?

//Painting codes:

void paint_test:: paintEvent(QPaintEvent * e)
{
QPainter painter(this);
painter.setPen(Qt::red);

QBrush brush(Qt:: Dense6Pattern);
brush.setColor(Qt::blue);
painter.setBrush(brush);

painter.setWindow(0, 0, 1000, 1000);
painter.drawRect(50, 50, 100, 200);

painter.setWindow(0, 0, 2000, 2000);
painter.drawRect(500, 100, 200, 400);

painter.setWindow(0, 0, 3000, 3000);
painter.drawRect(1350, 150, 300, 600);

painter.setWindow(0, 0, 4000, 4000);
painter.drawRect(2600, 200, 400, 800);

painter.setWindow(0, 0, 5000, 5000);
painter.drawRect(4250, 250, 500, 1000);
}

[jacek]

Indeed, it behaves strange. Especially when you resize the widget. It might be a result of some round-off errors, but IMO you should show this example to the Trolls.

Below is a working example:

#include <QApplication>
#include <QPainter>
#include <QWidget>
 
class Test : public QWidget
{
   protected:
      void paintEvent( QPaintEvent * )
      {
          QPainter painter(this);
          painter.setPen(Qt::red);
 
          QBrush brush(Qt:: Dense6Pattern);
          brush.setColor(Qt::blue);
          painter.setBrush(brush);
 
          painter.setWindow(0, 0, 1000, 1000); // try to comment out this line
          painter.drawRect(50, 50, 100, 200);
 
          painter.setWindow(0, 0, 2000, 2000);
          painter.drawRect(500, 100, 200, 400);
 
          painter.setWindow(0, 0, 3000, 3000);
          painter.drawRect(1350, 150, 300, 600);
 
          painter.setWindow(0, 0, 4000, 4000);
          painter.drawRect(2600, 200, 400, 800);
 
          painter.setWindow(0, 0, 5000, 5000);
          painter.drawRect(4250, 250, 500, 1000);
      }
};
 
int main( int argc, char **argv )
{
   QApplication app( argc, argv );
 
   Test t;
   t.show();
 
   return app.exec();
}

#include <QApplication>
#include <QPainter>
#include <QWidget>

class Test : public QWidget
{
   protected:
      void paintEvent( QPaintEvent * )
      {
          QPainter painter(this);
          painter.setPen(Qt::red);

          QBrush brush(Qt:: Dense6Pattern);
          brush.setColor(Qt::blue);
          painter.setBrush(brush);

          painter.setWindow(0, 0, 1000, 1000); // try to comment out this line
          painter.drawRect(50, 50, 100, 200);

          painter.setWindow(0, 0, 2000, 2000);
          painter.drawRect(500, 100, 200, 400);

          painter.setWindow(0, 0, 3000, 3000);
          painter.drawRect(1350, 150, 300, 600);

          painter.setWindow(0, 0, 4000, 4000);
          painter.drawRect(2600, 200, 400, 800);

          painter.setWindow(0, 0, 5000, 5000);
          painter.drawRect(4250, 250, 500, 1000);
      }
};

int main( int argc, char **argv )
{
   QApplication app( argc, argv );

   Test t;
   t.show();

   return app.exec();
}

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[jneuhaus20]

6 years later... I ran into this same problem, and only found this post referring to it. I solved it by doing the following:

painter.setWindow(0,0,_logicalWidth,_logicalHeight); //setting the logical window
 
QBrush brush(Qt::blue,Qt::Dense6Pattern);
 
//add a transform to the brush to undo the logical scaling
brush.setTransform( QTransform::fromScale( width()/_logicalWidth, height()/_logicalHeight) );
 
painter.setBrush(brush);
 
//and carry on drawing

painter.setWindow(0,0,_logicalWidth,_logicalHeight); //setting the logical window

QBrush brush(Qt::blue,Qt::Dense6Pattern);

//add a transform to the brush to undo the logical scaling
brush.setTransform( QTransform::fromScale( width()/_logicalWidth, height()/_logicalHeight) );

painter.setBrush(brush);

//and carry on drawing

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Hopefully this helps anyone who stumbles across it!