[help-3dldf] Re: Rotations

[Laurence Finston]

Hans Aberg wrote:
 
> 
> You may want to look up ray tracing algorithms. If one wants to emulate
> surfaces of different kinds, one way to do it is to assume that it is
> composed of a large number of suitably randomly positioned small mirrors.

Ray-tracing is one of the rendering techniques that I'll have to look into.  
I did look into this some time ago, but not very deeply.  It will be quite
awhile before I get the point where I can implement rendering within 3DLDF.  

My impression was that all of the practical and commonly used rendering
techniques work on pixel-data, that is, the image must be rasterized before
they can be applied.  I don't remember specifically whether this applies to
ray-tracing, but I think it does.

Ultimately I will have to perform rasterization in order to implement
high-quality rendering, but one of the constraints on 3DLDF is that I always
want it to be able to produce output in the form of MetaPost code.   While I
believe that high-quality rendering requires rasterization, there is quite a
bit one can do without it.  For example, it should be possible to implement
surface hiding by writing functions for "decomposing" geometric objects until
none of them intersect.  Then they can be rendered by a simple painter's
algorithm.   It may not be possible to do this at all in some cases, and in
others it may not be possible with a reasonable number of iterations.

I've already implemented reflection in a plane
for `Points', but  haven't gotten around to "propagating" it through the other
classes yet.  The problem is handling the case where the parts of a reflection
that extend beyond the boundaries of a section of the plane must be "cut off".
 This is related to the problem of "decomposing" objects for surface hiding.

I find it more interesting to work with non-rasterized data, but it seems that
beyond a certain point it will be necessary to use raster methods to get
high-quality results.

Laurence