Why does QPainterPath contains so few methods for drawing graphic primitives? How can I draw rounded rect on QPainterPath?

Let me describe what I want - I have some graphic primitives like rounded rect and want to draw them as a background for QGraphicsView, so I decided to draw them once to QPainterPath and draw it to view in QGraphicsView::drawBackground, but seems that QPainterPath miss methods I need (drawRoundRect for example).