On Sep 5, 2010, at 6:41 PM, David Bateman wrote:
David Bateman 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
D.
Well here is a first implementation that use method 1) above. I'm sure there are some
things missing, for example the method of using the "annotation" field of the
graphics objects to decide if they are included in the legend ass described in
http://www.mathworks.com/help/techdoc/creating_plots/braliom.html
and its seems the legend and the extra fields of the legend axis
'EdgeColor'
'Interpreter'
'Location'
'Orientation'
'String'
'TextColor'
as described in
https://savannah.gnu.org/bugs/?30461
The patch does however implement legends with different parents and horizontal
legends. So it fixes the bugs
29348, 30461 and in passing partially fixes the bug 30519.
It seems to work pretty well for the FLTK backend, and with a few hacks, it
works ok for me with the WXT terminal of gnuplot. It hasn't received a lot of
testing with gnuplot however, and I'm sending it now as I'm not sure I'll have
much time to work on this in the next couple of days.
So the questions I have are
a) If we keep the approach in this patch as described in method 1) above is the
need for FreeType and font_config to be installed an acceptable limitation?
These would become required rather than just optional
b) Is the approximate behavior of the text extents returned by FreeType for the
gnuplot terminal good enough? It needs more testing.
c) Why do I need to set the plot axis "activepositionproperty" to "position"
for the gnuplot backend to get the legend to display correctly? I see no reason for this need.
d) I worked internally in the legend function in "points" as by default the
text extents were returned in points. Would it be better to work in pixels as that is
what the figure position returns by default?
If the answer to a) and b) are "yes" I'll continue to work this up as a
changeset, cleaning out the old dead legend code and finishing fixing bug 30519 (rather
than just the minimum to get legends working). Otherwise I'll need to consider about how
to implement method 3) above in a clean manner.
Regards
David
I haven't looked into the details. The FLTK backend gave me the expected
result. Gnuplot gave me something else ... plots attached. I do have both
FreeType and font_config installed.
The script I used was ...
clf
x= 0:0.1:10;
plot (x, sin(x), x, cos(x))
legend ({"sin(x)", "cos(x)"}, "location", "northeast")
Tomorrow I'll look closer, but if anyone has an idea, I'd appreciate
suggestions.
Ben
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