These sources constitute the "Terminal-Independent Graphics" package,
or "TIG-pack".  The original sources were obtained from Mike Muuss of
the Ballistics Research Laboratory, formerly of Johns Hopkins Univ.
The present sources were completely re-coded from scratch by Doug Gwyn
at Geotronics Corp., Austin TX.  They are compatible with the JHU/BRL
versions, except that TIG output is always to stdout and the "fancy"
additions made by George Toth at JHU are not supported.

Several improvements were made during the re-coding process:
1) The 7th Edition UNIX standard C library is used.  G.C. has modified
the standard Ritchie compiler slightly; see "help c_news".
2) Bugs involving TIG UPA coordinates from 32768 to 65535 were fixed.
3) Bugs involving the DDA algorithms were fixed.
4) Other miscellaneous bugs (especially with the Trilog version of the
Versatec interpreter) were fixed.
5) A "pen down" followed by "pen up" results in a dot on all devices.
6) Interpreters for G.C. peripherals (Digital Engineering RG-512 &
VT640, and Trilog C-100) were created.
7) "rot" rotation, scaling, translation, & clipping filter was created.
8) "ovr" plot overlay filter was created.
9) "mulplot" filter for merging 11" plots on 22" plotter was created.
10) "help graphics" and "help tig_calls" are available.

Suggestions for future improvements:
1) Change TIG plot codes to use float instead of unsigned for coords.
2) Use a faster algorithm for vector-to-raster conversion (Versaplot?).
3) Device interpreters for Printronix & Tektronix (adapt "tri" & "vt").
4) Improve library routines (change floats to doubles, etc.).
5) Buffer RG-512 (like VT640); requires reducing line baud rate.
