How VLC implement the functionality of playing video in full screen mode ?

[Philip]

How VLC implement the functionality of playing video in full screen mode ?
when you double click the black rectangle ,VLC will play video in full screen mode ,
then if I doubleclick again ,it should return back .
http://www.freeimagehosting.net/st4su

so how to implement this functionality ?
for simplicity ,you can modify the following code to implement it ?thanks
NOTE ： showFullScreen()only affects windows

@import sys
from PyQt4 import QtGui, QtCore

class Player(QtGui.QMainWindow):
   
    def __init__(self, master=None):
        QtGui.QMainWindow.__init__(self, master)

        self.createUI()

    def createUI(self):
       
        self.Widget = QtGui.QWidget(self)
        self.setCentralWidget(self.Widget)

        self.VideoFrame = QtGui.QFrame()
        self.Palette = self.VideoFrame.palette()
        self.Palette.setColor (QtGui.QPalette.Window,
                               QtGui.QColor(0,0,0))
        self.VideoFrame.setPalette(self.Palette)
        self.VideoFrame.setAutoFillBackground(True)

        self.PositionSlider = QtGui.QSlider(QtCore.Qt.Horizontal, self)
        self.PositionSlider.setToolTip("Position")
        self.PositionSlider.setMaximum(1000)

        self.HButtonBox = QtGui.QHBoxLayout()
        self.PlayButton = QtGui.QPushButton("Play")
        self.HButtonBox.addWidget(self.PlayButton)
  

        self.StopButton = QtGui.QPushButton("Stop")
        self.HButtonBox.addWidget(self.StopButton)

        self.HButtonBox.addStretch(1)
        self.VolumeSlider = QtGui.QSlider(QtCore.Qt.Horizontal, self)
        self.VolumeSlider.setMaximum(100)
       
        self.VolumeSlider.setToolTip("Volume")
        self.HButtonBox.addWidget(self.VolumeSlider)

        self.VBoxLayout = QtGui.QVBoxLayout()
        self.VBoxLayout.addWidget(self.VideoFrame)
        self.VBoxLayout.addWidget(self.PositionSlider)
        self.VBoxLayout.addLayout(self.HButtonBox)

        self.Widget.setLayout(self.VBoxLayout)

 

if __name__ == "__main__":
    QtGui.QApplication.setStyle('macintosh')
    app = QtGui.QApplication(sys.argv)
    MediaPlayer = Player()
    MediaPlayer.show()
    MediaPlayer.resize(640, 480)
    sys.exit(app.exec_())
@