Documentation for backend("fltk")

[Michael D Godfrey]

I have been thinking about how to organize the documentation
for the fltk_OpenGL plotting feature.   Below is the beginning of an
updated plot.texi.  This indicates what I have in mind.  The main
problem, if the organization below seems reasonable, is how to
update the "Advanced Plotting" section.  One possibility is to
start with the features that are the same in both fltk and gnuplot
and then have 2 subsections which describe the features that
are specific to each plotting system.  This may get a bit confusing.

In any case, it would help if I could get reactions to this and
suggestions for a better structure.

First piece of plot.texi:

@node Plotting
@chapter Plotting
@cindex plotting
@cindex graphics

@menu
* Introduction::
* Basic Plotting::
* Graphics Handles::
* Advanced Plotting::
@end menu

@node Introduction
@section Introduction

Earlier versions of Octave provided plotting through the use of
gnuplot. This capability is still available.  But, a newer plotting
capability is provided by access to OpenGL.  Which plotting system
is used is controlled by the @code{backend} function.

@code{backend("fltk")} selects the FLTK_OpenGL system, and
@code{backend("gnuplot")} selects the gnuplot system.
The two systems may be used selectively through the use of the @code{backend}
property of the the graphics handle for each figure.  This is
more fully explained in @ref{Graphics Handles}.

@node Basic Plotting
@section Basic Plotting
=======================basic plotting as it is goes here==============
@node Graphics Handles
@section Graphics Handles

Graphics handles provide a uniform means of storing and manipulating
the properties of graphics objects.  The get and set commands are
used to obtain and set graphics handle properties.

A graphics handle property may be referenced by:

get(h, "property")

where h is a graphics handle and property is one of its properties.

The allowed properties of a graphics handle may be displayed by:
@code{get(h, "");}

Thus, for example,

@example
@group
h = figure();
get(h, "");
@end group
@end example

will display the allowed properties of the ``figure'' handle.
And,

@example
@group
aa=axes();
get(aa,"");
@end group
@end example

will display the allowed properties of the ``axes'' handle.

The root figure has index 0.  Its properties may be displayed by:

@code{get(0,"");}

The available graphics handles are: @code{figure}, @code{axes},
@code{line}, @code{text}, @code{patch},
and @code{surface}.
(@code{image} is still available, but is deprecated and will be removed.)


@node Advanced Plotting
@section Advanced Plotting
================Advanced Plotting with additional sections follows,
but with handle stuff move up to the section above==============

Michael