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Projected Light Maps in MaxImmerse
Projected light maps are used for effects like a slide projector or a stained glass window. There are two types of projected lights. A perspective projected type where the image is projected from a single nearby point (e.g. the slide projector) and a parallel projected type where the image is projected from far away (e.g. the stained glass window). Few graphics cards currently support perspective projected lights so they should be used cautiously. To specify these effects in Max an image needs to be placed in the Projector Map slot of a Direct or Spot light. Using a Direct light will result in a parallel projection, while using a Spot light will result in a perspective projection.
In NetImmerse, projected light maps act like dark maps so the slide projector and stained glass window examples are somewhat misleading. Projected light maps are multiplied with the base texture. The resulting combination is then multiplied by vertex colors or dynamic vertex lighting to get the final lit result. As with dark maps, if a portion of the projected light map is black, that area of the final result will be black and where the projected light map is white the base texture will show through. Applying a dark map in addition to a projected light map will cause the two multi-textures to be added together before they are multiplied by the base map (so their effects will sum together).
To use dynamic lighting with a projected texture, the negative space (usually the borders) of the projected map must be gray or some other non-black color. Just as with dark maps, this will allow the dynamic lights to influence whatever the projected light map does not directly light. If the negative space is black, dynamic lights cannot affect it.
In using projected textures, you may discover an unexpected (and perhaps undesirable) side effect: parallel and perspective projected texture projections are bi-directional. That is, the textures are projected infinitely in both directions. For example, a projected spotlight effect that is applied to an entire room will produce a circle of light on two walls—the wall that is directly in front of the projection, and the wall that is directly behind it. NetImmerse does support “clipped” projected textures, but this feature is not currently available via MaxImmerse. Therefore, to check to see if something is correctly displayed, you may have to get your programmer to enable clipped projected textures.
