PySide QtGui.QGraphicsWidget child-parent transformations

  • I have a question about using QtGui.QGraphicsWidget. In a given example I will try to describe my problem. There are two QGraphicsWidget instances inside the QtGui.QtGraphicsScene, of which one is a parent (app_widget.main_widget - blue one when running), and other one is its child widget (app_widget.subwidget - red one when running). If you run the program, with a Plus key on your keyboard you can transform widgets circularly through the states.

    # --coding: utf-8 --
    import sys
    from PySide import QtGui, QtCore
    class WidgetBase(QtGui.QGraphicsWidget):
        def __init__(self, parent = None):
            super(WidgetBase, self).__init__(parent)
        def set_background(self, color_hex):
            palette = QtGui.QPalette()
            color = QtGui.QColor()
            palette.setColor(QtGui.QPalette.Background, color)
    class AppWidget(WidgetBase):
        def __init__(self):
            super(AppWidget, self).__init__()
            self.main_widget = WidgetBase(self)
            self.subwidget = WidgetBase(self.main_widget)
    class Window(QtGui.QMainWindow):
        change_app_state = QtCore.Signal()
        def __init__(self, parent=None):
            QtGui.QMainWindow.__init__(self, parent)
            SCREEN_DIM = QtGui.QDesktopWidget().screenGeometry()
            self.app_scene = QtGui.QGraphicsScene(0, 0, SCREEN_DIM.width(), SCREEN_DIM.height())
            app_view = QtGui.QGraphicsView(self.app_scene)
            app_widget = AppWidget()
            app_widget.main_widget.resize(500, 500)
            app_widget.subwidget.resize(500 * 0.5, 500)
            self.machine = QtCore.QStateMachine()
            state1 = QtCore.QState(self.machine)
            state2 = QtCore.QState(self.machine)
            state3 = QtCore.QState(self.machine)
            state4 = QtCore.QState(self.machine)
            state1.assignProperty(app_widget.main_widget, 'geometry', QtCore.QRectF(0, 0, 500, 500))
            state2.assignProperty(app_widget.main_widget, 'scale', 0.5)
            state3.assignProperty(app_widget.main_widget, 'scale', 1)
            state4.assignProperty(app_widget.main_widget, 'geometry', QtCore.QRectF(0, 0, 1000, 500))
            trans1 = state1.addTransition(self.change_app_state, state2)
            trans2 = state2.addTransition(self.change_app_state, state3)
            trans3 = state3.addTransition(self.change_app_state, state4)
            trans4 = state4.addTransition(self.change_app_state, state1)
            trans1.addAnimation(QtCore.QPropertyAnimation(app_widget.main_widget, 'scale', state1))
            trans2.addAnimation(QtCore.QPropertyAnimation(app_widget.main_widget, 'scale', state2))
            trans3.addAnimation(QtCore.QPropertyAnimation(app_widget.main_widget, 'geometry', state3))
            trans4.addAnimation(QtCore.QPropertyAnimation(app_widget.main_widget, 'geometry', state4))
        def keyPressEvent(self, e):
            if e.key() == QtCore.Qt.Key_Plus:
    if __name__ == '__main__':
        app = QtGui.QApplication(sys.argv)
        window = Window()

    When scaling parent widget (changing 'scale' property - QtGui.QGraphicsWidget property inherited from QtGui.QGraphicsObject), a child widget also get scaled. But, when I change geometry of parent widget (changing 'geometry' property - QtGui.QGraphicsWidget property), child widget geometry remains unchanged.

    I am running Python 2.7.6, PySide version 1.2.1 and QtCore version 4.8.6.

    Why isn't a child widget always following parents transformations? Is there any way to scale only one axis of parent widget and get all children widgets to get scaled proportionally?

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    It will only follow it's parent widget if you put it in a layout that you set on the said parent widget. Otherwise it's up to you to handle the positioning and size of the child widget.