Solved PySide QtGui.QGraphicsWidget child-parent transformations

[nekitamtip]

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 --
# window.py
 
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()
        color.setRgba(color_hex)
        palette.setColor(QtGui.QPalette.Background, color)
        self.setPalette(palette)
        self.setAutoFillBackground(True)


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_view.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        app_view.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
 
        self.setCentralWidget(app_view)
 
        app_widget = AppWidget()
        app_widget.main_widget.set_background(0x50449558)
        app_widget.main_widget.resize(500, 500)
        app_widget.subwidget.set_background(0x50ff3300)
        app_widget.subwidget.resize(500 * 0.5, 500)

        self.app_scene.addItem(app_widget)
 
        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))
 
        self.machine.setInitialState(state1)
        self.machine.start()
 
    def keyPressEvent(self, e):
        if e.key() == QtCore.Qt.Key_Plus:
            self.change_app_state.emit()
 
 
if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    window = Window()
    window.showFullScreen()
    sys.exit(app.exec_())

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?

[SGaist]

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.