OpenGL line anti-aliasing

[Rik]

5/18/14

All,

The code in gl-render.cc was incorrectly turning off line anti-aliasing all
of the time.  This changeset restores the correct behavior
(http://hg.savannah.gnu.org/hgweb/octave/rev/be8d7721ac16).  Octave now
looks to use Full Scene Anti-Aliasing (GL_MULTISAMPLE) first.  If this is
not available then it tries to use the old built-in algorithm
(GL_LINE_SMOOTH).  I would welcome some comments about the desirablility of
this feature.  My screen does not support GL_MULTISAMPLE and I find that I
prefer jagged edges to the attempt by OpenGL to anti-alias the lines.  If
enough OpenGL implementations are bad it may be better to have jagged lines
if GL_MULTISAMPLE is not available.

--Rik

smooth.png
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jagged.png
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