[Octave-bug-tracker] [bug #44736] OpenGL / gl2ps printing alters or drops axis outline

[Dan Sebald]

Follow-up Comment #6, bug #44736 (project octave):

OpenGL, or Mesa?  OpenGL doesn't call out how the fill is done, just that
given the vertices, the polygon is convex

https://www.opengl.org/sdk/docs/man2/xhtml/glBegin.xml

Searching via grep, I see GL_POLYGON in the Octave gl-render code, there are a
couple uses of GL_QUADS, but I see no GL_TRIANGLE.  So Octave isn't the source
of triangulation, which was sort of confirmed by gnuplot not having
triangulated fills.

The way this is laid out in gl2ps-renderer.cc, it seems that gl2psBeginPage()
puts the OpenGL interface into some mode which redirects commands to the gl2ps
library.  After gl2psBeginPage() is


           opengl_renderer::draw (go);


which I'm assuming calls the code in gl-renderer.cc.

So, it doesn't seem like gl2ps interacts with Mesa or its drivers.  I'm more
inclined to think it is gl2ps doing the triangulation at this point.  If it
were a Mesa issue, I'd ask their discussion list what could be done.  But
gl2ps isn't something I want to mess with right now.


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