QPainterPath QTransform::map

Question

I would like to draw a rectangle with an angle. It works but when I change the angle, location of rectangle is changing somewhere else. I couldnt understand it. Does anybody give me a hand?

Here is my code :

QPoint point = QPoint(100,100); // has to be shown at this point
QSize  size  = QSize(30,30);
QRect rect = QRect(point,size);


QPainterPath Path ;
Path.addRect(rect);

QTransform t; 
t.rotate(myAngle);

QPainterPath newPath= t.map(Path);

QwtPlotShapeItem *Item = new QwtPlotShapeItem( "Shape Name" );
Item->setItemAttribute( QwtPlotItem::Legend, true );
Item->setRenderHint( QwtPlotItem::RenderAntialiased, true );
Item->setShape(newPath );
Item->setPen( Qt::black );
Item->setBrush( QColor("Grey") );
Item->attach(this);

I think map() function cause this problem. But i dont know why. Thanks for advices

Answer 1

QTransform::rotate rotates coordinate system using (0, 0) center point. Your rectangle is not at the center, so while rotating it will be significantly moved. You should place your rectangle at the center of coordinate system (point=(-15, -15)) and use t.translate after t.rotate to move rotated rectangle to appropriate position.