How is a projector handled in a Ray Tracing environment? I want to create a scene where a room includes a projector and a white screen.

How is a Ray Tracing environment functioning in such a setup? Is the light from the projector going through a slide and then the color reflecting on the white screen? If so, wouldn't any light ray bounce on that screen creating a mess?
Just treat it as a special case of a point light + shadow ray. Whenever a ray hits the screen (or any surface onto which you'd like to project the slide), fire another "projector" ray back towards the projector. If it is not obscured, then use the X &amp; Y angles (relative to the coordinate system of the projector) to look up a texture map of the slide.