Rotating a rectangle about its origin

[babu198649]

hi
How to rotate the rectangle about its origin. i have tried first by rotating the matrix and the calculating the distance between the topLeft() corner of a rectangle and the distance to which it has rotated ,and then translating it.I am unable to rotate about origin of rectangle, But i am able to rotate around the topLeft() corner of the rectangle.

Here is some code which rotates the about the topLeft() of a rectangle .Please help modify the code to make the rectangle rotate around its centre.

#include <QtGui>
 
class Widget : public QWidget
{
	Q_OBJECT
 
public:
	void paintEvent(QPaintEvent * event)
	{
		QMatrix matrix;
		QRect rect(20,20,150,100);
		matrix.translate(rect.left(), rect.top());
		static int degree=0;
		matrix.rotate(++degree);
 
		QPainter painter(this);
		painter.setMatrix(matrix);
		rect.setX(0);rect.setY(0);
		painter.drawRect(rect);
		painter.drawPoint(rect.center());
 
		QTimer::singleShot(100,this, SLOT(update()));
	}
};
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	a.setStyleSheet("QWidget{background: white}");
	Widget w;
	w.show();
	return a.exec();
}
 
#include "main.moc"

#include <QtGui>

class Widget : public QWidget
{
	Q_OBJECT

public:
	void paintEvent(QPaintEvent * event)
	{
		QMatrix matrix;
		QRect rect(20,20,150,100);
		matrix.translate(rect.left(), rect.top());
		static int degree=0;
		matrix.rotate(++degree);

		QPainter painter(this);
		painter.setMatrix(matrix);
		rect.setX(0);rect.setY(0);
		painter.drawRect(rect);
		painter.drawPoint(rect.center());
		
		QTimer::singleShot(100,this, SLOT(update()));
	}
};

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	a.setStyleSheet("QWidget{background: white}");
	Widget w;
	w.show();
	return a.exec();
}

#include "main.moc"

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