qt - QGraphicsView: preserve item size -

i realy newby in qt graphics-view
have large 2d scene should rendered using qgraphicsview. scene include several points of interest, each of should drawn marker (square, triangle, ellipse, etc.) problem marker should drawn in constant size despite scene transformations (zooming in or out). draw marker need combine it's position in scene coordinates , it's imensions in pixels inside paint method. efficient way this? surely can recalculate item position view coordinate each time scene zoomed or view resized, don't think correct solution. ideas?

assuming flags qgraphicsitems, set flag:

qgraphicsitem::itemignorestransformations