[Octave-bug-tracker] [bug #40054] FLTK: incorrect Z-order stacking for markers and images

[Michael Goffioul]

Follow-up Comment #1, bug #40054 (project octave):

Stacking is definitely a problem in OpenGL, for objects that lies in the same
Z-plane. Due to limited precision (OpenGL uses float), artefacts can appear,
especially when you start rotating a plot.

I'm not even sure there's a solution for that problem, at least an easy one.
To make sure that objects appear more or less correctly on screen, some offset
is applied in OpenGL, but then you get unexpected result if another object
lies in the same Z plane, like here.

For instance, to make sure the edges of a filled patch are visible, the
"filling" is slightly offset (along Z). Similar offset is (or can be, I don't
remember exactly) used to make sure markers appear on top of a line, and not
under it. This offset is of the order of OpenGL precision, but it's enough to
create unexpected result when multiple objects lie in the same plane.

Maybe one trade-off could be to use these slight offset only in 3D mode and
not in 2D.



    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?40054>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/