Interpolated shading does not appear to work with gnuplot.  Whether that is Octave's fault or gnuplot's fault I'm not sure.

A simpler example from the current development tree is

demo ("patch", 7)

I've attached pngs of the output from using FLTK or gnuplot with various backend terminals (X11, WXT).

Thanks for your reply!

Perhaps it is because the version I used is too low. Could you make a test for me please? Thanks!

1. I'm using gnuplot
2. I post an example script as follows:

[x,y,z] = meshgrid(-2:.02:2,-2:.02:2,-2:.02:2);
v = x.*exp(-x.^2-y.^2-z.^2);
xslice = 1; yslice = 1; zslice = -1;
slice(x,y,z,v,xslice,yslice,zslice)
colormap hsv
shading flat
print -dpng slice_flat.png
slice(x,y,z,v,xslice,yslice,zslice)
colormap hsv
shading interp
print -dpng slice_interp.png

Two figures are attached.
Thanks!

Using "slice" with "shading interp" causes different slices covered each other.
"shading flat" works well
Although "interp3" could be used to interpolate the data beforehand, it costs a lot of memory and the appearance is not as good as using "shading interp".
Two figures are attatched: one is obtained from using "shading interp" (slice_1.png), the other is from using "interp3" and "shading flat".