[Octave-bug-tracker] [bug #45594] gnuplot only supports 3-D triangular patches

[Rik]

Update of bug #45594 (project octave):

                 Summary: Color problem with patch () using gnuplot as
graphics_toolkit => gnuplot only supports 3-D triangular patches

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Follow-up Comment #2:

I've attached the script which causes the error to this bug report.  The
Octave file that issues the error is __go_draw_axes__.m. 


669                  if (nd == 3)
670                    if (numel (xcol) > 3)
671-->                   error ("__go_draw_axes__: gnuplot (as of v4.2) only
supports 3-D filled triangular patches");
672                    else


If this is just an unsupported feature of gnuplot, then this is not an Octave
bug.  But it is possible that Octave is not converting things correctly.

In this case, the patch object 'zdata' property is all zeros.  This is correct
because they are in fact 2-D patches drawn at Z=0.  However, because the zdata
is not empty, the number of dimensions is calculated as 3.  A simple
workaround for this particular example is


hp = get (gca, "children")
set (hp, "zdata", [])


The dimension check is done in C++ code in calc_dimensions is graphics.cc


  int nd = 2;

  if (go.isa ("surface"))
    nd = 3;
  else if ((go.isa ("line") || go.isa ("patch"))
           && ! go.get ("zdata").is_empty ())
    nd = 3;
  else


Now maybe the code should check whether all the zdata is 0 before deciding
that an object is 3-dimensional, although that is a much more expensive test
than just is_empty.

It can also be solved by going back to the original script_patch_problem.m and
not specifying zdata of all zeros in the patch.  Then the patch is, correctly,
2-D.



(file #34518)
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Additional Item Attachment:

File name: script_patch_problem.m         Size:0 KB


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