[Octave-bug-tracker] [bug #39535] FaceAlpha property not working for OpenGL backend

[Pantxo Diribarne]

Follow-up Comment #20, bug #39535 (project octave):

@Markus: the attached cset conditions the use of GL2PS_OCCLUSION_CULL on the
presence of transparent objects polygons (not lines) in an axes. With this
cset, the following example from comment #5 works for me in printout even
though it does not work onscreen:


[x,y,z] = meshgrid (-2:0.2:2, -2:0.2:2, -2:0.2:2);
val = x.^2 + y.^2 + z.^2;
fv1 = isosurface (x, y, z, val, .6);
patch (fv1, "FaceAlpha", .3, "FaceColor", "r", "EdgeColor", "none");
fv2 = isosurface (x, y, z, val, 1);
patch (fv2, "FaceAlpha", .3, "FaceColor", "g", "EdgeColor", "none");
view (3);
print /tmp/tst.svg
open /tmp/tst.svg


The following example with surfaces shows that printing "mostly" renders as on
screen for surfaces too


clf ();


subplot (2,2,1)
h = surface ();
xd = get (h, "xdata") + .5;
yd = get (h, "ydata") + .5;
zd = get (h, "zdata") * 0;
set (h, "zdata", zd);
surface (xd, yd, zd);

title "2D no transparency\nSpurious lines in printout"

subplot (2,2,2)
h = surface ();
xd = get (h, "xdata") + .5;
yd = get (h, "ydata") + .5;
zd = get (h, "zdata") * 0;
set (h, "zdata", zd);
surface (xd, yd, zd, "facealpha", 0.5);

title "2D transparency"

subplot (2,2,3)
h = surface ();
xd = get (h, "xdata") + .5;
yd = get (h, "ydata") + .5;
zd = get (h, "zdata") + 1;
## push axes background away so that it does not interfere
zlim ([-1 2]); 
h = surface (xd, yd, zd, "facealpha", 0.5);

title "3D, transparent drawn last"

subplot (2,2,4)
h = surface ("facealpha", 0.5);
xd = get (h, "xdata") + .5;
yd = get (h, "ydata") + .5;
zd = get (h, "zdata") + 1;
h = surface (xd, yd, zd);
## push axes background away so that it does not interfere
zlim ([-1 2]); 

title "3D, transparent drawn first"

print /tmp/tst.svg


(file #42222)
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Additional Item Attachment:

File name: txtback4.patch                 Size:7 KB


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