[Octave-bug-tracker] [bug #48435] transparent patches can only be obtained by printing to svg with gnuplot

[Francesco Potortì]

URL:
  <http://savannah.gnu.org/bugs/?48435>

                 Summary: transparent patches can only be obtained by printing
to svg with gnuplot
                 Project: GNU Octave
            Submitted by: pot
            Submitted on: Thu 07 Jul 2016 12:40:43 PM CEST
                Category: Plotting with OpenGL
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.2
        Operating System: GNU/Linux

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Details:

The following code should produce two partially transparent,  overlapping
triangles of different colours delimited by solid lines:

hold on
fill([0 2 1], [0 0 2], 'b', 'facealpha', 0.3)
fill([0 2 1], 1+[0 0 2], 'r', 'facealpha', 0.3)

Note that Postscript generally cannot handle transparency, so we are using X
and SVG.

When using fltk:
- on X the triangles are completely transparent, no colour
- printing to svg is the same, and additionally the lines are dashed

When using gnuplot 5:
- on X the triangles are coloured as expected, but opaque
- printing to svg the result is as expected

The only way to obtain the expected result is to use gnuplot and print to SVG.




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