Matlab compatible legends for FLTK/Gnuplot backends?

[David Bateman]

As it seems to me that the blocking feature for 3.4.0 is the support of 
legends in FLTK, I've been looking at writing a matlab compatiable, or 
at least more compatible than currently, legend function. I however want 
this function to not be specific to a backend and I want it to work with 
both FLTK and the gnuplot backend and be implemented entirely as a 
frontend function. I'm however blocked in that goal when calculating the 
extents of the text strings.

How I'm trying to implement this function is to create an axis object, 
with the "tag" property set to "legend" and the userdata with a 
structure with a field pointing to the axis the legend is attached to. 
The position, limits, etc of the legend axis are initially arbitrary and 
into this axis I write all of the text strings. The object of doing this 
is to calculate the extent of each of the text strings so that I can 
then select an optimal positioning of the keys in the legend, and only 
after that resize the axis, position it and write the symbols. The 
get_extents method of the graphics.cc(text) class fills in the "extents" 
property of the text objects. However, it relies on having both FreeType 
and font_config installed. I'd rather not add new dependency for the 
gnuplot backend and in any case why should I assume that FreeType will 
give extents that are compatible with gnuplot. So from here I see I have 
one of four choices

1) Accept the FreeType and font_config dependencies, making these 
essential for any plotting with legends in Octave. However, this might 
not be ideal for the gnuplot backend,

2) Try and find another means of implementing the get_extents method of 
the the graphics.cc(text) class that will be used if FreeType isn't 
installed (or for backends that don't use FreeType), but this is likely 
to be approximative

3) Give up on trying to have a legend function that is implemented 
entirely in the frontend and  continue to use gnuplot itself for the 
legend insertion for the gnuplot backend. I'd probably implement the 
missing horizontal legend orientation in gnuplot and make the gnuplot 
legend more compatible with matlab in this case.

4) Get someone on this list to tell me I'm a bloody idiot and there is 
another means of getting the text extents that will be correct (at least 
approximately) for all backends.

I'm kind of hoping for 4), but failing that help in choosing which of 
the other three options would be appreciated

D.