Globe Saver
Ron Blanford, TRW Inc.

What is it?

This is a screensaver module for use with Samuel Streeper's BackSpace application.  You must already have installed BackSpace.app on your system prior to installing this module.  BackSpace.app may be available via anonymous ftp from the archives at cs.orst.edu or nova.cc.purdue.edu, but I haven't been able to find it.  

How do I install it?

This module is distributed in source form.  To install it, bring up a terminal window and cd to the module directory.  Then type 
	make INSTALLDIR=<BackSpace path> install
replacing <BackSpace path> with your BackSpace installation directory (by default $HOME/Apps).

What does it look like?

GlobeSaver displays an equatorial view of the spinning Earth.  The Earth rotates once every 2 seconds.  As it rotates, the Earth glides across the screen in straight arcs, bouncing off the screen boundaries.

The Earth image has been generated from topographic data, with negative elevations colored in shades of blue and positive elevations in shades of green and brown.  The artistic credit goes to John Stevenson of TRW.

How does it work?

Globe Saver implements the GlobeView class as a subclass of SlidingImage which comes standard with BackSpace.  SlidingImage handles the motion trajectory of the Earth across the screen.  The added functionality provided by GlobeView is to replace the still image with an Icon animation file.  The animation of the rotating Earth is in the supplied Globe.anim file.

You may change the default animation file by specifying an alternate in the defaults database.  At a shell prompt, type
	dwrite BackSpace animFile <file path>
replacing <file path> with the full pathname of the desired animation file.  The defaults are only read at module launch time.

The default animation update frequency is 18 frames per second.  This may also be changed in the defaults database, by typing
	dwrite BackSpace animSpeed <frames per second>
replacing <frames per second> with the desired update frequency.

What bugs or limitations are there?

The animation is initially slow while the frames are being rendered and cached.  After the first rotation, the performance becomes more acceptable.

The default animation file path is that of the BackSpace application directory (<BackSpace path>/BackSpace.app/Globe.anim) even if the GlobeSaver module is installed in a separate BackSpaceViews directory.  This default location may be overridden using the dwrite mechanism described above.

The motion parameters of the SlidingImage class are determined by the dimensions of the default image selected in the Preferences Settings panel.  This remains the case in GlobeSaver, even though the display is being generated from the animation file.  For best coverage of the screen, therefore, the default image should be set to one of the frames within the animation file.

Who owns this module?

You do.  If you have any questions, send me Email and I might answer if I can find the time.

	Ron Blanford
	blanford@spf.trw.com