This function computes and (by default) displays a histogram
of the values of the function x.
An object of class "funxy"
describes a function of spatial location. It is a function(x,y,..)
in the R language, with additional attributes.
The function hist.funxy is a method for the generic
function hist for the class "funxy".
The function is first converted to a pixel image using as.im,
then hist.im is called to produce the histogram.
Any arguments in ... are passed to as.im
to determine the pixel resolution,
or to hist.im to determine the histogram breaks
and to control or suppress plotting.
Useful arguments include W for the spatial domain,
eps,dimyx for pixel resolution, main for the main title.