On Wed, Sep 1, 2010 at 10:14 PM, David Bateman <address@hidden> wrote:
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
I'm not the one which will tell you #4. Text extents are highly
dependent on the text rendering technique, and unless gnuplot has some
way of conveying its text extents back to octave (which I doubt --
gnuplot is designed to be standalone, not a backend), you have no way
of knowing.