PyQt instant startup screen trick

As most of us already know most PyQt4 apps are taking quite sometimes at start up and most of the time users are getting initial black screen while it's loading, this is just not only the case with Python apps but all the apps on N900. Nokia has used a trick to snapshot of apps start up screen and load image instantly when the app icon is pressed, which give users an impression that apps was started up instantly but in reality they were not. (modest, note, sketch, control panel, application manager, pdfviewer, worldclock, xterm, and calculator are using this trick). So why don't we apply the same trick on our apps to make it look fast at startup? Well, Most of us don't even know the trick is there and some debates whether this is a good idea or not, but I for one rather see a false startup image than a black screen. So below is the instruction to make your Python Qt app fly at startup on N900 device.

There are three basic things to make it work:

  1. A D-Bus service file (name whatever e.g. yourapp.service) in "/usr/share/dbus-1/services/" folder even though yourapp is not using D-Bus related service at all and it should look like this format in yourapp.service.
    [D-BUS Service]
  2. Adding "X-Osso-Service=what.ever.yourapp" in your yourapp.desktop file in "/usr/share/applications/hildon/" folder, something like this.
    [Desktop Entry]
  3. Lastly, A function code in your app to take a snapshot of your app startup screen when it starts up the first time or when it exits whichever your prefer. Below is an basic example of PyQt4 app code which take a snapshot of the screen at start up if it's not already exist and save it into '"/home/user/.cache/launch/what.ever.yourapp.pvr" (p.s. the file name has to match with your X-Osso-Service, and D-BUS Service Name plus .pvr extension).
    #!/usr/bin/env python2.5
    # -*- coding: utf-8 -*-
    from PyQt4.QtGui import *
    from PyQt4.QtCore import *
    import osso # only needed for osso_initialize
    class MainWindow(QMainWindow):
        def __init__(self, parent = None):        
            self.dbus_service_name = "what.ever.yourapp"  #must be the same as your X-osso-service in yourapp.desktop file
            self.osso_c = osso.Context(self.dbus_service_name, "0.0.1", False)
            is only needed if your app is not launched from,
            Otherwise, your app will be terminated after ~ 2mins running
            don't ask me why :)
            self.osso_c = osso.Context(self.dbus_service_name, "0.0.1", False)
            QMainWindow.__init__(self, parent)
            self.centralwidget = QWidget(self)
            the rest of your code here....
        def takeScreenShot(self):
            pvr = "/home/user/.cache/launch/%s.pvr" % self.dbus_service_name
            if not QFile.exists(pvr): # skipped if it's already there
                QPixmap.grabWidget(self.centralwidget).save(pvr, 'png') # tell it to grab only your self.centralwidget screen, which is just window screen without the menu status bar on top. 
    if __name__ == '__main__':
        import sys
        app = QApplication(sys.argv)
        YourApp = MainWindow()
        YourApp.takeScreenShot() # run this after the