[Octave-bug-tracker] [bug #44181] Tesselation lines visible in plot output of patches

[Dan Sebald]

Follow-up Comment #13, bug #44181 (project octave):

Thinking about the characteristic of the line artifact, I got to wondering why
it isn't a bright white pixel that is showing through.  (On my printer, it
actually is a rather bright single-pixel line half way through the
hexadecagon.)  I then began to suspect it is that smoothing is applied to rid
sharp edges.

Viewing the patch4.pdf file in Acroread, go to the Edit:Preferences... menu
and uncheck "Smooth Line Art" under the Rendering group.  The lines
disappear.

XPDF also has such an option de-selection, but it must be done at the command
line:


xpdf -aaVector no patch4.pdf &


The lines go away but the vector renderings look rather bad.  When vector
smoothing is on, XPDF does something worse than Acroread.  Some of the lines
come out darker than the blue polygon, not lighter.  One would think if XPDF
is smoothing the edges of the triangles it would combine the white background
and blue to make something lighter between edges.  The darker lines are inside
of the black outline of the octagon.  Strange.

Is there a way for PostScript code to force vector smoothing off?  There are
all sorts of things like image interpolation, image masking, stencil masking,
etc.

Are these relevant?

http://www.geuz.org/gl2ps/

GL2PS_POLYGON_OFFSET_FILL
    Emulates the GL_POLYGON_OFFSET_FILL functionality. The value of the offset
is taken as the current value of the corresponding OpenGL offset (set with
glPolygonOffset).
GL2PS_BLEND
    Emulates the GL_BLEND functionality. (Warning: this might change in future
releases.)
GL2PS_POLYGON_BOUNDARY
    Not implemented yet.


https://www.opengl.org/sdk/docs/man3/xhtml/glPolygonOffset.xml
Name
glPolygonOffset — set the scale and units used to calculate depth values

If not, I'll go with closing this bug report as Will Not Fix.  The source of
the problem ultimately goes back to the triangulation of the polygon.

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