No QGraphicsScene proper coordinates

[harmodrew]

And how can I tell the view to "stretch" the scene object to the view's viewport?
for example if I assign a scenerect of 100x100 with the top letf corner as (0,0) to the scene and then draw a line from 0,0 to 100,100, I'd like the view to show the diagonal of the screen (so the scene is shown entirely into the view and is "stretched" into the view")...

Thanks

[wysota]

And how can I tell the view to "stretch" the scene object to the view's viewport?

I suggest you look at the available API of QGraphicsView.