Path: chuka.playstation.co.uk!news
From: "Mario Wynands" <mario@sidhe.co.nz>
Newsgroups: scea.yaroze.programming.3d_graphics
Subject: Re: Lighting
Date: Tue, 14 Jul 1998 11:22:45 +1200
Organization: Sidhe Interactive
Lines: 62
Message-ID: <6oe4jh$n307@chuka.playstation.co.uk>
References: <6odou2$ajq2@scea>
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Steve Spiller wrote in message <6odou2$ajq2@scea>...
>Is there a way to create/simulate point or spotlight lights?  Looking
>through the library docs it appears you can only have ambient or parallel
>lighting...


Funnily enough I am working on that exact same thing at the moment (avoiding
finishing off some slightly complicated particle systems code :) ), so I
should be able to offer some guidance.

Firstly, start with a struct something along the lines of

typedef struct
{

 int light_type; // point, directional, or spot

 long da, db, dc;  // distance attenuation coefficients
 long aa, ab, ac;  // angle attentuation coefficients for spotlights

 CVECTOR    colour; // colour of light source
VECTOR direction;  // direction vector for spot and directional
 GsCOORDINATE2 *coord2; // pointer to coordinate system

} Light;

Make sure all the polygons in a scene you want affected by the lights are
the coloured vertex type (as Craig Graham suggests).  When you go to sort an
object into the ordering table, iterate through all polygons and light each
vertex by applying the (abstract) formula :

final_colour = sumof( light_color * dist_attenuation_factor *
angle_attentuation_factor * ( light_ray_vector . vertex_normal))

where

dist_attenuation_factor = 1 / ( da + db * distance + dc * distance_squared )
angle_attenuation_factor = 1 / ( aa + ab * distance + ac *
distance_squared )

or something like that anyway :)

This method will happily support directional, point, and spot lights.  You
may find this slow in complex dynamic scenes, and remember lighting is on a
per vertex basis so you may get some artifacting with spotlights, but the
results should be good enough.

There are several things you could add to this such as diffuse calculations,
light 'switches', and ambient lighting etc, but this should be enough to get
you started.


Cheers,

Mario Wynands

Director/Project Manager, Sidhe Interactive
Sony Playstation Software Development House

Email mario@sidhe.co.nz Website www.sidhe.co.nz