Hands On DarkBASIC Pro - Digital Skills

FIG-30.17
Lights
Surface Normals
FIG-30.18
Visible Polygons
We can even use several cameras, switching between each to change what the user
is seeing on the screen. Unlike real life, there's never any chance of seeing a camera
in the view produced by a second camera - all virtual cameras are invisible!
DarkBASIC Pro creates and positions a single camera automatically at the start of
every program that uses 3D objects. The exact position of the camera depends on
the positioning of the 3D objects, since the camera normally places itself in order
to see the objects that have been created. However, as the programmer, you can take
complete control of the camera and thereby determine just exactly what appears on
the screen.
We can even set up the lights we want to use to illuminate our new world - just like
placing lights on a movie set. By positioning various types of lights in just the
correct positions, we can create any type of atmosphere we want - from dark and
mysterious to bright and sunny. Like cameras in the 3D world, the lights are
invisible, but the effects they create are not!
To help calculate the effect of lights on the individual polygons of a 3D object, a
set of normals are maintained. A surface normal is a vector from the centre of a
polygon perpendicular to the surface of that polygon. Every polygon in an object
has an associated normal (see FIG-30.17).
A normal for
each polygon
Normals are stored as mathematical expressions and are not part of the visible
structure of the model.
In principal every polygon can have two surface normals: one on the top side and
one on the bottom. However, often models only use a single normal - on the side
facing outwards.
When using surface normals to calculate how an object should be lit, we sometimes
get a rather faceted appearance, with an obvious jump in shading from one polygon
to the next (see FIG-30.18).
752 DarkBASIC Pro: 3D - Concepts and Terminology