XGAP consists of a C program xgap
(in the following xgap
in
typewriter style refers to this C part) separate from GAP, and of some
libraries written in the GAP language. xgap
is started by the
user and launches a GAP job in the background. It then talks
to this GAP job. Especially it displays all the output which comes from
GAP in the communication window and feeds everything the user types in
this window into the GAP job.
But there is also some communication with the GAP job about the graphics
that should be displayed. Because GAP has no concept of putting graphics
on the screen, this part is done by xgap
. Therefore there is a protocol
between the GAP part of XGAP running in the GAP session and xgap
which is embedded in the input/output stream. The user does not notice
this. xgap
stores all windows and graphic objects and does all the work
necessary for displaying windows and managing user communication and so on.
The GAP part of XGAP also stores all graphical information, but in
form of GAP objects. The user can inspect all these structures and use
them in own programs. Changes in these structures are transmitted through
the communications protocol to xgap
and are eventually displayed on the
screen. User actions like mouse clicks or keyboard events are caught by
xgap
and transmitted to the GAP job via function calls that are
``typed in'' as if the user had typed them. So the library can work on them
and change the GAP objects accordingly.
Technically, XGAP is a share package and one of the first commands that
is executed automatically within the GAP session is a
RequirePackage("xgap")
call. This reads in the extra XGAP
libraries. They are found in the pkg/xgap/lib
subdirectory, normally in the
main GAP directory. The files contain the following:
window.g
sheet.g[di]
color.g[di]
font.g[di]
menu.g[di]
gobject.g[di]
poset.g[di]
ilatgrp.g[di]
meataxe.g[di]
The user normally does not need to know this or the details of it. However,
it is important to understand that the program xgap
is highly machine or
at least operating system dependent. There is no generic way to access
graphics across different platforms up to now. XGAP should run on all
variants of Unix with the X Window System Version 11 Release 5 or
higher. As of now XGAP does not run on Microsoft Windows or MacOS. It is
also definitely not easily ported there, because some important features
that are used within XGAP are missing there (such as pseudo terminals).
There are currently no plans underways to do work in this direction.
However, portations are very welcome! If you would like to put some work
into this, please contact Max Neunhöffer (email:
max.neunhoeffer@math.rwth-aachen.de
).
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xgap manual