How to rotate items in a QGraphicsScene while keeping them upright

[wysota]

Could you provide a clearer explanation of what you want to achieve? As now it seems you want to rotate things without them rotating which doesn't make much sense.

[stampede]

If I understand you right, you simply want to rotate the line mid point:

QLine line = ...;
QTransform t;
t.rotate(angle); // actually just figure it out yourself how to rotate around specified point
const QPoint mid = (line.p1()+line.p2)/2;
const QPoint rotated_mid = t.map(mid);
line.translate( rotated_mid-mid );

QLine line = ...;
QTransform t;
t.rotate(angle); // actually just figure it out yourself how to rotate around specified point
const QPoint mid = (line.p1()+line.p2)/2;
const QPoint rotated_mid = t.map(mid);
line.translate( rotated_mid-mid );

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You cannot rotate the start and end points separately, it will change the line direction (if angle != 0).

[wayfaerer]

Thank you! That worked, although I actually wound up finding a simpler solution for my specific case. The lines are on top of QGraphicsItems that *do* rotate normally. So all I had to do was set each line's parent as its corresponding QGraphicsItem, then set the ItemIgnoresTransformations flag on the lines. I think I'm going to wind up using your approach elsewhere, though. Thanks again.