Strangeness with PM3D

[Ethan A M. <merritt@u.washington.edu>]

In trying to figure out why some of the output files produced by the
canvas driver are so large, I stumbled across a strange pm3d problem
that seems to affect many drivers.  It shows up in several of the demos,
but the most extreme case is transparent_solids.dem.

The issue is this line in pm3d.c
  693:         /* set the color */
  694:         set_color(gray);

The line is clearly necessary in the general case, but there must be one
or more conditions in which the loop containing this line is executed
many times even though no pm3d quadrangles are actually drawn.
This results in huge numbers of useless color setting commands in the
output file.  For instance, if you run it through the postscript driver
   set term post color solid
   set output 'ts.ps'
   load 'transparent_solids.dem'

you will find in the output file lines like the following:
%pm3d_map_begin
.4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4729 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g .4218 g  ... [snip] %pm3d_map_end

where all of that is on one line of >15000 characters!
Deleting these spurious lines has no visible effect on the rendered plot, 
but reduces the file size considerably.  

How can we get rid of this unwanted output?


-- 
Ethan A Merritt