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Light Sources

The default light position is at the viewpoint. The ILLUMINATION command defines other positions. Up to 9 positions, in addition to the default position, may be defined. Only one light is in effect at any time. The RLIGHT command recalls defined lights (the default light—numbered 0— is always defined). A light can also be recalled in the Retrieve Light submenu of the Projection Menu .

Non-default light positions can result in shadows. The ray tracing interpolation algorithm used in the Fine and Coarse modes does not recognize whether the pixels at the corners and center of the interpolation box are in shadow or not. As a result, the shadows may be fuzzy. Use of the Super interpolation mode will ensure well-defined shadows.

Lights should not be placed within opaque objects. Except for the default position, Sabrina does not check if this is the case at present. Non-default positioned light sources do not work correctly when cutter bodies are present and within lattices. Positioned light sources are not used when geometry testing is in effect.

The background color, which is used when the ray does not encounter an opaque object, is not affected by the light properties.

All lights are white. The color of each pixel is the color of the object at the pixel position modified by an overall intensity as described below. We will add colored lights and permit multiple light sources in the future.