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Creating a splash screen with no window manager borders

01-Jul-03 08:00 GMT

Question: How do I create a splash screen with no window manager borders?

While my Motif application is initializing I'd like to display a splash screen that shows a product logo and related information. In particular, I'd like this splash screen to have no window manager borders around it.

This can be achieved using two different approaches.

One option is to use the "XmNmwmDecorations" resource to turn off the Motif Window Manager decorations on the shell that you have assigned as the splash screen. For example:

	 XtVaSetValues(shell_widget, XmNmwmDecorations,
		       MWM_DECOR_ALL |
		       MWM_DECOR_TITLE |
		       MWM_DECOR_MENU |
		       NULL );

The above will only work if your application is running with the Motif Window Manager (mwm) or CDE. Given that there are now many other popular window managers it is no longer safe to assume your users will be running mwm. Consequently a more general solution is required.

A window manager neutral solution to this problem is to use the "XmNoverrideRedirect" resource on the shell containing your splash screen. The purpose of this resource is to instruct the window manager to ignore this particular shell. If this resource is set on the shell the window manager will not set its size or position and will not add window decorations to it.

Since the window manager is ignoring this window you will likely find that it appears in the top left hand corner of your screen. If this not what you want you will need to explicitly set X and Y co-ordinates for the shell. For example:

	XtVaSetValues(shell_widget, XmNoverrideRedirect, TRUE, NULL);
	XtVaSetValues(shell_widget, XmNx, 502, XmNy, 65, NULL);

If displaying the splash in the center of the screen regardless of the type and size of the display is important to you, consider adding some code to find out the dimensions of the display and calculate the X and Y co-ordinates based on this. Details on how to get the display dimensions as the basis for these calculations are available here.

You may also find that your initialization sequence is so fast that the splash screen isn't displayed long enough for the user to see it. If this is the case you may want to call a timeout procedure after the splash screen is displayed that unmanages your splash screen and manages your main dialog after a suitable delay.

Other Issues

There are a number of residual issues to do with splash screens that need consideration in addition to the problem, answered above, of removing window manager decorations.

Firstly, a splash screen needs to be visible and operative even though the rest of the interface (the real front end) may not exist at this point in the application.

In order to get the screen to work, we require two things:

  • the screen will have to be realized, even though the main front end isn't.
  • there needs to be an X event loop to process expose (etc.) events for the screen, but at this point we are outside the control of the main application X event loop.

The classical solution to the first issue involves a slight adjustment to the widget class hierarchy. Typically, an application has one application (or session) shell for the main front end, with subsidiary top level/dialog shells created as required. Here, in order to display the splash screen, we will need the application shell to be realized, but we don't want it visible. The solution is to create an empty application shell, and use top level shells throughout for front end screens. In other words, the application shell no longer contains a visible widget hierarchy.

The second problem will only be solved by using a temporary X event loop. The splash screen will simply fail to expose itself otherwise. The logic will read along the lines of:

	Boolean      splash_screen_required = True;
	XtAppContext app_context = ... ;

	while (splash_screen_required) {
		XEvent event ;

		XtAppNextEvent(app_context, &event);

Where splash_screen_required will need to be set programmatically as required. This however will block the application from performing whatever initialization the splash screen is supposedly masking. There are various ways of threading the initialization process through the temporary loop, for example, a work or timer procedure can be added onto the application context, and this procedure can perform the application initialization without interfering with events to the splash screen interface. Typically, the initialization process would be phased, otherwise a large single initialization step would potentially block X event processing. An ideal solution may well involve real multi-threading.

The last piece of the picture is related to keeping the interface concurrent. Typically, a splash screen will contain a progress bar of some description, whether a true third party component such as the XRT/Gear ProgressBar widget, or a suitably configured Motif 2.1 Thermometer Scale. Changing the value of the scale or progress indicator needs to display immediately, and not when an X event is next processed. The solution to this problem is straightforward: a call to XmUpdateDisplay(Widget) will force all components with pending expose events to expose themselves immediately, even though the program logic may not be processing X events at the point of call.


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