LIGHTING SYSTEM ON GRIDMAP


Lighting system is based on phong illumination model developed in early
1980's :). Light value on a gridmap depends on three values:

1.	Ambient light			(sun/moon/stars)
2.	Diffuse light			(torches and such)
3.	Specular light			(reflected light .. or maybe we 
					 don't want to code mirrors :> )
					 
The algorithm for calculating the light (or darkness) intensity is:

I = I_ambient + I_diffuse + I_specular

Let's make some example for the lighting scale:

I = 
	+40:	magical brightness
	+30:	bright daylight
	+20: 	cloudy weather or indoors
	+10:	torch light
	  0:	twilight (one can barely see)
	
Negative values are total darkness where players are unable to see without
being able to see in the dark.

We need to have some kind of lighting map in the gridmap code to speed
things up.


	VISIBILITY
	
In the gridmap players may see as far away as has been allowed by the code
unless:

1.	There is some obstacle that prevents direct line of sight
2.	There is some obstacle that reduces the visibility

Visibility is assigned some fixed value (100 for example) and is decreased
in every grid square light travels through. For example wilderness would reduce 
the visibility value by 50, which would allow seeing through two squares of 
wilderness.

++ Dazzt @ 29.03.1998