DXF2DKB - AutoCAD DXF File to DKB 2.0+ Ray-Tracer .DAT File Translator

Version 1.0 Written by Aaron A. Collins
Version 1.01 Updated to DKB 2.10, etc. By Drew Wells

This program is designed to take in AutoCAD DXF (Drawing eXchange Format)
files and convert them to DKB scene description data files.  This is the
first release of this program so it has some limitations.

To be the most universal, it is compiled for 8086 opcodes with optional
8087 support if it is detected.  The speed difference is not significant,
the biggest speed limiting factor will be disk access/transfer speed.

The biggest problem when doing something like this is that AutoCAD has some
truly Non-3D constructs (such as CIRCLES and LINES) that are nearly impossible
to represent in a 3-D renderer.  I have taken the "cheese log" approach to
making 3-D constructs that approximately represent the 2-D shapes.  For
instance, I use VERY skinny triangles (nearly degenerate) to make "LINES" and
"3DLINES", very small spheres to represent "POINTS" and very short cylinders
to make "CIRCLES".

The more proper 3-D constructs like "TRACE", "SOLID", and "3DFACE" are most
easily represented as one or two TRIANGLES in DKB, so an object consisting
of these should essentially be correct.

Unfortunately a fairly prevalent 3-D construct in ACAD is the "POLYLINE",
which can get really complex and have B-Spline curves or Polygon Patch Meshes
defined by the VERTEX points, so they aren't implemented yet.

I strongly suggest isolating only one "object" per DXF file you write out,
(that may be made up of many primitives, however) mostly because a bounding
box is automatically created to surround the entire object.  This speeds up
the intersection decision making process of the Ray-Tracer considerably.
Each object should have it's own bounding volume if more than one is included
in a scene, or the bounding box becomes fairly useless.

I have attempted to filter out degenerate TRIANGLES before they can get to
and choke the parser in the Ray-Tracer.  Degenerate TRIANGLES are ones which
have two of the three points the same (i.e. a "LINE"!).  Since there is no
way to Ray-Trace a "LINE" in 3-D space, these are sick entities which would
make the Ray-Tracer enter the Olympic Cookie-Toss.  At least they used to,
before we added code to detect them and exit after the parsing process if
any are detected in the scene.  You should rarely have to remove them manually
any more.  Note though, that the Tracer uses a different mathematical method
to detect degenerates than I do here, so there is the remote possibility that
one or two might slip by.

You will have to edit the output file of the program to add in a VIEW_POINT
and a LIGHT_SOURCE or two, at the very minimum.  I eventually will add code
to translate these too, but for now you're on your own.

If you use Design-CAD 3-D instead of AutoCAD, you must use their external
DXF.EXE program to convert the file to DXF format before feeding it into
this program.

Anyway, if anyone wants to take a crack at "filling in the blanks" and doing
some of the other primitives, go ahead and send it back to me!  I'm including
the AutoCAD publicly released DXF.DOC file describing the DXF file format in
EXHAUSTIVE detail.


Future Enhancements (The Eternal List of Things To Do):

1.  Add in code to parse the current viewpoint from the current viewport
    from the DXF file while whizzing past the HEADER and TABLES section
    and write out a proper DKB "VIEW_POINT" construct.

2.  Add code to handle POLYLINES, if really done properly, would handle
    the flags that identify splines and patch meshes, etc. and perform the
    surface tesselation required to make these patch areas between VERTEX'es
    into TRIANGLE'd polygons.

3.  Add code to make "DECLARE" statements out of defined BLOCK's, and then
    instance the BLOCK wherever indicated by the subsequent BLOCK entities.

4.  I doubt it will ever handle "TEXT", as this would require a stroke-type
    of character generator routine, or something.

5.  Make it pick out the AutoShade entities for "CAMERA" and "LAMP" and
    use these for VIEW_POINT and LIGHT_SOURCE's over any viewpoint defined.