I have compiled the current dev version of Octave (hg id b85a46745298 of today) on my Linux system:

• I can confirm Dmitri's observation that the demo code in comment #0 does NOT have those white lines any more.
• BUT when I use my mouse to rotate this 3d plot, then I DO see those white lines come back, quite often.

A demo script to reproduce those white lines in current dev Octave is this (just a changed view command):

clear, close all;
graphics_toolkit qt % fltk is the same, gnuplot is fine

x = [-3:1:3];
y = x;
[xx, yy] = meshgrid(x,y);
zz = xx .* yy;
zz(zz < 0) = 0;

surf(xx, yy, zz, 'EdgeColor', 'none');
view(30,85);
grid off;

I will attach a screenshot of this tilted 3d plot with current dev Octave (under Linux).

This happens with Octave 4.2.1 and the OpenGL toolkits . Here is how to reproduce it:

clear, close all;
graphics_toolkit qt % fltk is the same, gnuplot is fine

x = [-3:1:3];
y = x;
[xx, yy] = meshgrid(x,y);
zz = xx .* yy;
zz(zz < 0) = 0;

surf(xx, yy, zz, 'EdgeColor', 'none');
view(2);
grid off;

In the resulting (2d view on a) 3d surface plot, there are some additonal white lines visible. (They are also visible in other 3d view orientations.) Those white lines should not be there.

I have observed this with Windows 7 as well as with Ubuntu 16.04 linux.

The generated 3d plot of Matlab does not show those white lines. But I think this is not only a compatibility issue, but an Octave plotting bug on its own. Those white lines simply shouldn't be there, they spoil the appearance of the whole 3d plot.

I will attach 3 screenshots from Octave results (under Win7 and Ubuntu 16.04) as well as Matlab results (Win7).