Re: Matlab compatible legends for FLTK/Gnuplot backends?

[Ben Abbott]

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

legend-fltk.pdf
Description: Adobe PDF document

legend-gnuplot.pdf
Description: Adobe PDF document