Re: [Matplotlib-users] filled contours: progress, a minor bug (?), and a point of curiosity

[Eric F. <ef...@ha...>]

John,

>     Eric> Having solved that problem, I am getting more optimistic
>     Eric> about being able to come up with a usable filled contour
>     Eric> capability fairly quickly.  Still no promises, though.
> 
> Great -- be mindful of the contourf matlab docstrings.  Strict
> adherence is not required, but it is nice to be compatible where
> possible.

I have the basic filled contour functionality working, with the 
following caveats, comments, and questions:

0) I've done only the simplest of testing so far.

1) There is a fundamental difference in strategy between Matlab's 
contour patch generation algorithm and gcntr.c: Matlab makes all patches 
as simply connected regions without branch cuts, but gcntr polygons have 
branch cuts.  This means that we can't use the polygon edges; if one 
wants line contours at the contour levels, they must be drawn 
separately, by asking gcntr for lines, as contour does.  My inclination 
is to leave it this way: the user can simply call contourf to get the 
filled regions, and then call contour to add lines as needed.  Typically 
I draw lines at only a few of the color boundaries, and sometimes I draw 
additional lines within colored regions, so this is the way I normally 
use matlab contourf and contour anyway.

2) In the present version, there is much too much duplication of code 
between contour and contourf in axes.py; I copied the contour function 
to contourf, modified what I needed to, and moved only the 
ContourMappable class out to the module level.  I would like to factor 
out more of the common code.

3) The docstrings in axes.py are driving me nuts--lacking proper 
indentation, they make it very difficult to find the function 
definitions.  I presume this is because of the way boilerplate.py is 
generating the pylab.py functions and their docstrings.  I haven't 
looked at boilerplate.py (I haven't used it yet at all), but I suspect 
it would be easy to change things so that it would handle properly 
indented docstrings.  Is it OK if I do this?

4) ToDo: it is not standard in matlab, but for filled contouring I 
always use a matching colorbar--essentially a colorbar contoured with 
the same levels and colors as the contour plot itself, rather than one 
that shows the whole colormap.

5) ToDo: I haven't tried to do anything with region masking yet; maybe I 
will get to it soon, since it is something I need.

5) gcntr.c uses global variables, which presumably means that it will 
fail if called from more than one thread at a time.  Longer term, should 
I/we/someone modify it so that this not the case?  Or is this 
characteristic of other routines used by matplotlib, so there is no 
point in worrying about gcntr.c in particular?

6) When the time comes to send you my modifications, how should I do it: 
diffs, or complete files? Send to you directly, or to the list?  If you 
would prefer diffs, please give me an example of the exact diff command 
options to use.  (I am working with matplotlib-0.72.1 as a starting 
point.)  Modified files will include axes.py, pylab.py (and/or 
boilerplate.py), _contour.c, and an example.

Eric