[Octave-bug-tracker] [bug #42534] No lines when printing plot (fltk)

[Andreas Weber]

Follow-up Comment #28, bug #42534 (project octave):

Hi Bradley, the "drawnow..." hack directly saves the output of gl2ps to
test.eps (EPS is the default output of gl2ps in octave) without using the
fltk-pipeline. So no ghostscript or epstool is used. Only if you use other
formats like SVG, PS, PNG, JPEG... ghostscript is used to convert the .eps
(This is only true when using graphics_toolkit fltk)

If you want to help debug this just 2 ideas I have what could be the problem:

1.) The white axes background and the lines in the foreground are drawn so
tight in z-direction that the algorithm for OCCLUSION_CULL in gl2ps thinks the
lines are behind the white background and removes them. You could remove
GL2PS_OCCLUSION_CULL in gl2ps-renderer.cc
(http://hg.octave.org/octave/file/14bb81940528/libinterp/corefcn/gl2ps-renderer.cc#l98),
and see if the generated eps contains the lines in the file and if they are
hidden behind white triangles. Another entry would be to see how the
z-position is calculated in gl-renderer.cc::draw_line.

2.) Another idea is that there are timing problems where gl2ps finishes before
your graphic driver painted all OpenGL content. I've fixed this on the default
branch in cset http://hg.octave.org/octave/rev/c9f960441513 using glFlush() to
force the execution of GL commands. You can try this by replacing
gl2ps-renderer.cc in your MXE build with the one on the default branch.

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