[manual] suggested addition to pcolor description

[Petr Mikulik]

> >Gnuplot does interpolation in pm3d by splitting each quadrangle into smaller
> >quadrangles. You can try the following example that demonstrates
> >"shading flat" and "shading interp":
> >
> >pcolor([1 2; 3 3])
> >shading interp
> >shading flat
> >
> >Therefore, I've written the following patch:
> >https://sourceforge.net/tracker/index.php?func=detail&aid=2558565&group_id=2055&atid=302055
> >[ 2558565 ] pm3d interpolate 0,0
> >The animated demo there shows color surface transformations; Octave would
> >use for its "shading interp" the option
> >	set pm3d interpolate 0,0
> 
> I think the attached files look good ... but can you describe what has been
> changed.  The results (in your email) look very similar to what the current
> gnuplot sources produce.

It is desired to achieve higher resolution plot with an alternative "pm3d 
interpolate" option. Let us suppose that "continuous" colour gradient on the 
map/surface would need edge size of at least 200 pixels on screen window. 
Then
	a=hilb(4);
	pcolor(a);
would need
	set pm3d interpolate 50,50
while
	a=hilb(100);
	pcolor(a);
would need
	set pm3d interpolate 2,2

With the new patch, you can set
	set pm3d interpolate -200,-200
and gnuplot will ensure at least 200 points in both cases, i.e. Octave 
passes the sampling to the drawing backend.

Currently,
	set pm3d interpolate 0,0
is equivalent to 200 points.

---
Petr Mikulik