Alien Ettiquette
		or
   How the aliens should behave.

1. Solitary Prowling.

	Required action:
	Simulate a sort of random roaming of the rooms and corridors looking
	for intruders, with no active cooperation between aliens.
		
	Possible solutions:
	a) Picking a control point at random and going all the way there, 
	then picking a new point and going to there, and so on.
	
	b) Keeping a one-position memory of the last c.p. visited, preventing
	the alien from back-tracking pointlessly. At each control point
	reached, a new one is selected at random from those adjoining the
	current one.
	
	c) Just pick a new point at random adjoining the current one and go
	there, not bothering about whether it has just been there or not.
	
	Characteristics of solutions:
	a) Aliens tend to roam very widely quite quickly, and might easily
	find the players within seconds of starting a level even when
	initially positioned a long way away.
	
	b) Aliens will tend to spread out more slowly, provided there are
	many 'loops' and junctions in the area. With lots of long corridors
	with few junctions, the aliens will become more seperated much more
	quickly.
	
	c) Aliens will wander backwards and forwards and never really get
	anywhere no matter what the design of level is like.
	
2. Solitary Attack.

	Required action:
	An alien has seen an enemy and has decided to attack.
	
	Possible solutions:
	a) While the enemy is visible the alien heads towards it, returning
	to its earlier mode of behaviour when no enemy is visible, with
	some flags set to indicate the enemy has been sighted.
	If another closer target presents itself, the alien will attack it
	instead.
	
	b) While the enemy is visible the alien heads towards it,
	remembering where the enemy is all the time. If the enemy should
	vanish, the alien will head to the place it last saw the enemy. If
	it reaches this place and it still cannot see the enemy it reverts
	to previous mode of behaviour, with flags set indicating the enemy
	has been sighted.
	
	Characteristics of solutions:
	
	a) Aliens are easy to 'lose' in a maze-like level with lots of
	corners.
	
	b) Aliens, particularly fast ones, are difficult to shake off. If
	they are moving faster than you are you might have a real problem
	and have to stand, or run, and fight.
	
3. Cooperative search.

	Required action:
	Aliens know the enemy is out there somewhere and want to find them.
	They work together to search everywhere pretty thoroughly.
	
	Possible Solutions:
	a) Aliens move from c.p. to c.p. using method 1b, except when faced
	with a junction rather than a corridor. In that case, aliens wait
	until there are enough of them at one junction to go down every
	exit EXCEPT those from which any of them has arrived
	
	b) Similar to above except that aliens faced with more unexplored
	exits than there are aliens to explore them will pick exits randomly
	and keep moving.
	
	Characteristics of solutions:
	
	a) Aliens are cautious about venturing alone into new areas and tend
	to wait for backup. Of course, it may happen that this never arrives
	and so after some prearranged time limit the alien my start to prowl
	independantly.
	
	b) Aliens keep moving and exploring and tend to find the enemy
	more quickly.

4. 'Wait for backup'

	Required action:
	A lone alien finding the enemy decides to wait until there are more
	of its fellows around before attacking. It should keep out of sight
	and possibly signal to other aliens.

	Possible solutions:
	a) Aliens remember the last position where they were unable to see
	any enemy and retreat to that point when the enemy is sighted. If
	seen and attacked, the alien will definately call to its fellows
	and may decide to attack or retreat.
	
	Characteristics of solutions:
	a) Aliens are cunning and reluctant to be drawn into confrontations
	where they do not have the advantage.

Notable behaviour patterns obtained by combinations of the above:
=================================================================

1b and 2b make aliens very persistant, particularly if the enemy sighted
(ES) flags make it speed up when prowling. If no cooperation is allowed this
should give a moderate difficulty level which could offer real problems if
the player's tactics are poor (eg telling everyone to split up and run
away from the aliens).

1c and 2a make aliens very stupid, frequently giving up the chase to just
wander aimlessly around. For early levels only.

3a and 4a make aliens very cautious and reluctant to enter into
confrontations.

3b with 2b and screams and so on makes aliens individually aggressive, and 
if not dealt with quickly will lead all the others to you

3a/b with actual communication ie telling other aliens where you are rather
than just making a noise, means that if an alien sees you, and you dont
leave sharpish, all the other aliens are going to turn up and slaughter you.
Makes for a difficult level.