PySide2: Understanding QGraphicsItemGroup.setScale()

galou_breizh

Here is a little example that doesn't do what I expect it to do. I expect a 50x50 px² circle at (500, 1000) px. What I get is a single pixel.

#!/usr/bin/python3
# -*- coding: utf-8 -*-
"""Show an incomprehension in setScale for QGraphicsItemGroup."""

from PySide2 import QtCore
from PySide2 import QtGui
from PySide2 import QtWidgets

point_size = 0.1  # In real-world units.

# Get entrypoint through which we control underlying Qt framework
app = QtWidgets.QApplication([])

scene = QtWidgets.QGraphicsScene()
group = QtWidgets.QGraphicsItemGroup()
scale = 500  # 1 real-world units = 500 px.  !! Has no apparent effect.
group.setScale(scale)
pen = QtGui.QPen(QtCore.Qt.red)
brush = QtGui.QBrush(QtCore.Qt.blue)
x = 1  # Real-world units.
y = 2  # Real-world units.
top_left = (x - point_size / 2, y - point_size / 2)
ellipse = QtWidgets.QGraphicsEllipseItem(
    QtCore.QRectF(*top_left, point_size, point_size))
ellipse.setPen(pen)
ellipse.setBrush(brush)
group.addToGroup(ellipse)
scene.addItem(group)

view = QtWidgets.QGraphicsView(scene)
view.show()

# Start Qt/PySide2 application. If we don't show any windows, the
# app would just loop at this point without the means to exit
app.exec_()

Gojir4

Hi @galou_breizh ,

It seems it works (windows) after moving group.setScale(scale) below group.addToGroup(ellipse)

group.addToGroup(ellipse)
group.setScale(scale)

Edit: It works also by putting the scale on the ellipse object. ellipse.setScale(scale)

galou_breizh

Thanks for the super-quick answer!

Ok, I don't get it but the result is now different. However, it's still not the correct result. What I get is something between a circle and a square with red stroke (size 500x500 px²) filled with white color with a 50x50 px² blue circle in the middle cf. screenshot . The same as in my other post: https://forum.qt.io/topic/110762/pyside2-filling-not-scaled#

Gojir4

@galou_breizh I answered in the other post. But it's not a good way to duplicate post for the same issue. Please try to avoid it in the future, thanks