Shadows and reflections are closely related to transformations and projections. A shadow is the projection of the outline of an object onto a surface or surfaces, and reflection in a plane is an affine transformation.
3D rendering software generally implements shadows, or more generally, shading, reflections, and certain other effects using methods involving the calculation of individual pixel values. Surface hiding is also often implemented at the pixel level. 3DLDF does no scan converting ((see Accuracy), and hence no calculation of pixel values at all, so these methods cannot be used in 3DLDF at present.
However, it is possible to define functions for generating shadows and reflections within 3DLDF by other means.
I have defined the function Point::reflect() for reflecting a
Point in a Plane, and have begun definining versions for
other classes.
However, in order for reflections to work, I must define functions for breaking up objects into smaller units. This is also necessary for surface hiding to work properly.
For MetaPost output, I will have to implement shadows, reflections, and surface hiding in this way. However, 3DLDF could be made to produce output in other formats. There are two possibilities: implementing rendering functionality within 3DLDF, or interfacing to existing rendering software. If I decide to do the latter, there are again two possibilities: having 3DLDF write output in a format that a renderer can input, or linking to a library supplied by a rendering package.
I haven't yet decided which course to pursue. However, in the long run, I'd like it to be possible to use 3DLDF for fancier graphics than is currently possible using MetaPost and PostScript alone.