			G.O.D.   INSTRUCTIONS

MENU BAR

-FILE: SAVE a system to disk, OPEN one previously saved on disk,
 or EXIT the program

-NEW: creates a new configuration (see below for more)

-CONFIGURE: configures the system  
When you choose this option a new edit window will appear with the current
system. The default editor is joe, but you can change it uncommenting the
appropriate line in the proc called by the config button command.

-ZOOM: zooms a region of the space 
 2D mode: choose the ZOOM menu-bar option, then select the region to
 zoom by clicking the left mouse button in the top-left corner of the region;
 move the cursor to the bottom-right corner, then click again. The region
 selected will be zoomed to fit the window.
 3D mode: sorry, still under development
 HOW TO UNZOOM: press the pause button, then the zoom menu button.

CONTROL SECTION

SPINNING CUBE
These three scales set the viewpoint. They are active only in 3D mode.

MODE
These buttons select the display mode: 2D or 3D

SCHEME
These buttons choose the numeric scheme used to compute the objects' 
positions. There are 3 schemes: Prof., sucker and art. The first is the 
correct one, the others are modifications that generate very interesting 
drawings.  

PARAMETERS
	Gravitational const.    : sets the gravitational constant
	dt                      : time step for numeric integration
	max acc.                : maximum acceleration allowed for the objects

PALETTE
This scale sets the palette of colors to use to draw objects' trajectories

REW/PLAY/PAUSE buttons
The play button starts simulation, or restart it after that the pause button
has been pressed; the pause button suspends simulation (e.g., to change some
parameters); the rew button "rewinds" the system to its initial configuration.

DOMAIN
Entries to set the integration domain

TRACK
You can choose to track trajectories with a color proportional to the VELOCITY
of the object, to use a different color for each OBJECT, or not to track
trajectories (NONE -- this is not too much interesting, but allows you to
change the viewpoint while the system is running...)

COLLISION
You can choose what have to happen when two objects collide. They may 
never collide (treated as 0-dimensional points) have an elastic collision (not
too realistic, but very funny ! :-).

SPACE
This sets the kind of space where the system runs. It can be a real space
(RxR or RxRxR -- depend on the mode selected) or an hipertoroidal space,
that is when an object exits the space from one side it will re-enter it
by the opposite side.


MISC.

HOW TO CREATE A NEW SYSTEM

-2D:
Choose the NEW option from the menu bar; a new window will appear.
To place a planet or a sun you have to set its mass and radius by moving the 
scales or typing the values into the entries. The difference is that the 
scales allow you to enter only integer values, while the entries allow real
values.
Once you have chosen mass and radius, move the mouse into the space window 
and to the place where you want to place the object (in the top-left corner
of the window will appear its coordinates) then click mouse button 1 to place
a sun, button 2 to place a LOCKED sun (see below) or button 3 to place a
planet, as shown in the window's figure. Initial velocities are all null.
(If you have a 2-buttons mouse it's your business how to make it !! :-)
Once you have placed all the objects, push the "DONE" button to return to the
control panel to start simulation.
This is a kind of try-me mode, just to experiment the program. To set up a
system is better to create an input file (see below for more)

-3D:
( not yet activated -- edit a text file with the initial configuration and
load it)

LOCKED SUNS
As each other object a sun is subject to the gravitational force of the other
objects, so it can move. However in some simulations it could be better to
ignore this and consider a sun a "fixed" object, to simplify the system and
focus the attention on the behaviour of the planets.

G.O.D. SYSTEM FILES
A system file is a file containing all the information concerning a system.
It is created automatically when you save a system with the file-save option,
or you can write your own system with a text editor. View the examples and
the default.god file to see how to make one.

TROUBLESHOOTING
-Make Failure: this could be due to the paths in the #include section of the C-code
or of the TCL-TK code. Check the location of the include lib files in your system
and modify the wrong paths.
-Font error: if you get an error like " fond adobe... not found" delete the line in the
TCL code, or try to set up a font supported by your system
-Configure failure: maybe the default editor called by the function is not supported
by your system. Uncomment the appropriate line to choose your.

KNOWN BUGS
When started the first time the program should load the file 'default.god'.
For unknown and still undetected reasons it loads only the scalar constants,
while the arrays containing initial positions and velocities not.
Reload it.
Please report bugs to the addresses below.

TO DO
-Imakefile to help the porting on others platforms.
-3D graphical object placing and initial velocity setting
-3D zoom

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If you used this program and found it interesting, please let us know.
You can send e-mail either to
	
	fportera@oink.dsi.unive.it 
		or to
	crossi@moo.dsi.unive.it ,

or postcards, letters (or pigeons, smoke signals, tam-tam or whatever media
you like) to

Filippo Portera 
via Cellini no. 2/a
30038 spinea - VENEZIA
ITALY

or

Claudio Rossi
via F. dall'Ongaro no. 2
30175 marghera - VENEZIA
ITALY 


(money, checks, jewels, gold nuggets and Murano glasses are welcome !  :-)


Have fun!

Claudio & Felipe

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CREDITS

Many thanks to Livio Rossani, who drew most of the bitmaps; Andrea Torsello,
who explained us the mechanics of 3D elastic collisions; Albert TrueTable, who
gave us the formulas for 2D representation of a 3D space; Adrian Nye, whose 
book "Xlib Programming Manual" helped us in so many occasions that is 
impossible to cite them one by one; Mario Jorge Silva for the "fileselect.tcl"
procedure (found with such a wonderful instrument like WWW and downloaded
from ftp.aud.alcatel.com), which allowed us to save lots of time to build an
our own file browser.

Finally we would like to thank John K. Ousterhout for the creation of those 
powerful instruments named TCL and TK. 
