[Octave-bug-tracker] [bug #48873] Matlab incompatibilities in plot routines revealed through dump_plot_demos

[Rik]

Follow-up Comment #26, bug #48873 (project octave):

I can confirm that svg output works for transparency, although it has other
issues when the linewidth is < 1.

This seems to be a gl2ps issue.  In gl2ps-print.cc we start out gl2psBeginPage
by including the option GL2PS_NO_BLENDING.  That alone disables the alpha
channel.  However, I commented that out and re-compiled and it still doesn't
work.

I think the problem may be that we call


  glEnable (GL_BLEND);


in the code when displaying on-screen.  But for printing I think we need to
use the gl2ps version and call


  gl2psEnable (GL2PS_BLEND);


We already do this for other GL/GL2PS options such as GL_LINE_STIPPLE.  There
appear to be only 3 places in gl-render.cc where the value for GL_BLEND is
changed.  But even so, this will take a bit of work to get it right.  Pantxo
can probably tell me whether this idea makes sense or is only a false path.


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