Scripting Guide - SAS

456 Three-Dimensional Scenes Chapter 13
Lighting and Normals
Figure 13.16 Spotlight
SPOT_CUTOFF
Light
Source
In addition to the cutoff angle, you can control the intensity and direction of the light distribution in the
cone. SPOT_DIRECTION specifies the direction for the spotlight to point; SPOT_EXPONENT influences how
concentrated the light is.
Lighting Models
Lighting models are specified with the Light Model command.
Light Model( parameter, value,...,value )
Light models specify three attributes of lights.
• The global ambient light intensity
• Whether the viewpoint is local or is an infinite distance away
• Whether lighting calculations should be performed differently for the front and back faces of objects.
Table 13.3 on page 454 shows the three valid parameters for the Light Model command.
Table 13.4 Light Model Parameters and Default Values
Parameter Default Value Meaning
LIGHT_MODEL_AMBIENT (0.2, 0.2, 0.2, 1) Ambient RGBA intensity of the entire scene
LIGHT_MODEL_LOCAL_VIEWER 0 (false) how specular reflection angles are computed
LIGHT_MODEL_TWO_SIDE 0 (false) nonzero values imply two-sided lighting
Normal Vectors
Normal vectors point in a direction perpendicular to a surface. For a plane, all normals are the same. For a
more complicated surface, normals are more complicated. JSL enables you to specify the normal vector for
each vertex. These normals specify the orientation of the surface in space, necessary for lighting calculations.
Accurate normals assure accurate lighting.