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[Octave-bug-tracker] [bug #44181] Tesselation lines visible in plot outp

From: Dan Sebald
Subject: [Octave-bug-tracker] [bug #44181] Tesselation lines visible in plot output of patches
Date: Fri, 20 Feb 2015 04:50:06 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0 SeaMonkey/2.15

Follow-up Comment #1, bug #44181 (project octave):

I just tested this here and found similar behavior.  I printed out the data
and the vertices look in order, the faces are in order as well (faces indexes
the vertices to describe the polygon).  I looked at the code, and do see a
large hunk of code about tesselation in gl-render.cc.  Whether that is called
in this case, I'm not sure.  Doesn't the graphices library accept all the
vertices at once and draw without tesselation?

I'm wondering about the border of the green octagon being drawn on top of the
blue hexadecagon.  That is similar for both FLTK and Qt, but for gnuplot
terminal the border of the green octagon is also behind the blue hexadecagon. 
One of them is wrong.  I don't see any inputs to patch in the demo that would
control the depth of the border versus the depth of the face.  Another bug
report?  It may be in the same file and part of the same code.  E.g., in
gl-render.cc is this note:

          // NOTE: Push filled part of patch backwards to avoid Z-fighting
          // tesselator outline.  A value of 1.0 seems to work fine.  Value
          // can't be too large or the patch will be pushed below the axes
          // planes at +2.5.

By the same logic, the code might be pushing the filled part backward past all
patch outlines as well.


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