.TH xlander "" "" "X Application"
.PC "A lunar landing simulation with a twist"
.ie n \{\
\fBxlander [\-controls \fIstring\^\fB] [\-fn \fIfont\^\fB] [\-gravity \fIplanet\^\fB]
	[\-lateral \fIvalue\^\fB] [\-repeat] [\-retro \fIvalue\^\fB]\fR
\}
.el \{\
\fBxlander [\-controls \fIstring\^\fB] [\-fn \fIfont\^\fB] [\-gravity \fIplanet\^\fB] [\-lateral \fIvalue\^\fB] [\-repeat] [\-retro \fIvalue\^\fB]\fR
\}
.PP
.B xlander
is a lunar-landing simulation for X.
In this game, a landing craft is orbiting above the rugged surface of
a planet.
As the game begins, the lander begins to fall toward the planet's surface.
You can affect the lander's motion by firing thrusters.
Each firing of a thruster consumes some of your finite supply of fuel.
Your object is to maneuver the lander onto a landing pad before you run
out of fuel.
.PP
You must land the lander on the landing pad with as little motion as possible:
too much speed laterally or vertically, and you crash.
The landing pad is visible as a square on the ground
with a flag planted at one corner.
The shadow of the lander is projected onto the ground, which allows you to
see how high it is and where it will touch down.
Although you can land anywhere on the surface, you must land on the
landing pad to get points.
After each successful landing, the program gives
you a score based on your vertical and lateral speeds, refills your
fuel tank, and restarts the simulation at a higher difficulty level
(by increasing the force of gravity).
If you crash, the game shows your final score
and allows you to either start over or quit.
.PP
The lander is equipped with five thrusters:
four directional thrusters, which control lateral motion;
and one retroactive thruster, which fires
downward to produce upward momentum.
The retro thruster consumes more fuel than do the directional thrusters,
as it produces more thrust to combat the force of gravity.
.PP
Each thruster is activated by pressing and holding a particular key.
By default, the space bar fires the retroactive thruster, and
the 8, 2, 4 and 6 keypad keys fire the front, rear, left and right
directional thrusters, respectively.
You can re-map these keys by using the command-line option
.BR \-control ,
which is described below.
You can also use the keyboard arrow keys to
fire directional thrusters if you like.
.SH "Gauges and Indicators"
The screen displays a number of gauges and indicators
that tell you the lander's status.
The following describes the gauges from left to right on the panel:
.IP "Heading Indicator"
This circular indicator tells you the lateral direction of
the lander.
.IP "Velocity Gauge"
This gauge tells you your rate of ascent or descent.
.IP "Fuel Gauge"
This tells you how much fuel you have left.
.IP "Radar Screen"
This screen shows the lander's position relative to the landing pad.
.SH Options
.B xlander
recognizes the following command-line options:
.IP "\fB\-controls \fIstring\fR"
This links the thrusters to given keys on the keyboard.
.I string
must consist of five characters, in the following order:
forward thruster, backward thruster, left thruster, right thruster,
and retro thruster.
The default string is ``8246 ''.
If you are used to the editor
.BR vi ,
you might want to use the control string ``kjhl ''.
.IP "\fB\-fn \fIfont\fR"
Use
.I font
to display the text used by the program.
.IP "\fB-gravity \fIplanet\fR"
Simulate gravity of a particular planet or other heavenly body.
.I planet
can be any of the following:
.BR moon ,
.BR earth ,
.BR mercury ,
.BR venus ,
.BR mars ,
.BR jupiter ,
.BR saturn ,
.BR uranus ,
.BR neptune ,
or
.BR pluto .
The default is
.BR moon .
This option also automatically
adjusts the amount of retro thrust to suit the gravity of the planet,
unless you override it using the option
.BR \-retro .
.IP "\fB\-lateral \fIvalue\fR"
Specify the amount of thrust, in feet per second squared,
that the four lateral thrusters give.
.IP \fB\-repeat\fR
Do not turn off key repeat for the duration of the game.
Because thrust is activated by holding down keys,
.B xlander
turns off auto key repeat during the game.
This prevents keypress events from getting backed up in the queue.
When the game exits, it restores the original key-repeat mode.
This option disables this behavior.
.IP "\fB\-retro \fIvalue\fR"
Specify the amount of thrust, in feet per second squared,
that the retroactive thruster gives.
.SH "See Also"
.B
X applications
.R
.SH Notes
The authors of
.B xlander
are not physicists or mathematicians.
They do not guarantee accuracy, so you probably should not use
.B xlander
to polish up your lunar-landing skills.
.PP
.II "Riddle, Paul"
.II "Friedman, Mike"
.B xlander
was written by
Paul Riddle (paulr@umbc3.umbc.edu) and Mike Friedman (mikef@umbc3.umbc.edu).
