[Octave-bug-tracker] [bug #44111] Images not printed when there's a 3D axes in the figure

[Pantxo Diribarne]

Follow-up Comment #10, bug #44111 (project octave):

@Rik: you are right. gl2psEnable  doc says:

"The value of the offset is taken as the current value of the
corresponding OpenGL offset (set with glPolygonOffset)".

As I understand, PolygonOffset data, that we set in our gl-renderer, are not
written in the feedback buffer (see [1]) that gl2ps will parse/interpret/draw
*when we call gl2psEndPage()*, i.e. after all our drawing have been done. As a
consequence gl2ps has to force some additional informations to be written
"live" in the feedback buffer while we are "drawing". That is why we should
gl2psEnable/Disable each time we change the offset.

The above could be done through something like:


void
gl2ps_renderer::set_polygon_offset (bool on, float offset)
{
  if (on)
    {
      opengl_renderer::set_polygon_offset (on, offset);
      gl2psEnable (GL2PS_POLYGON_OFFSET_FILL);
    }
  else
    {
      gl2psDisable (GL2PS_POLYGON_OFFSET_FILL);
      opengl_renderer::set_polygon_offset (on, offset);
    }
} 


By looking at the gl2ps.c code I think it is how gl2psEnable was intended to
be used. Unfortunately, I think that gl2ps currently only stores the values of
the offset (factor/unit) that was in place the last time you called
"gl2psEnable (GL2PS_POLYGON_OFFSET_FILL);", before gl2psEndPage(). If you
think it is worth I can ask for details on gl2ps mailing list. Thoughts?

[1] http://bittar.free.fr/OpenGL/opengl/glPolygonOffset.html : glPolygonOffset
has no effect on depth coordinates placed in the feedback buffer. 

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