[matplotlib-devel] matlab_helpers and screen dpi/figsize refactored

[John H. <jdh...@ac...>]

In the process of rationalizing the way figure size and dpi is handled
between the various backends, I had to make a number of changes to the
matplotlib backend.  This will pave the way for an rc file in which
the user can set the dpi, figsize, font, etc.. properties for each
backend.  But it required some changes to the Gcf and FigureManager
setup.  It actually simplifies writing a new backend, but will require
some relatively painless changes to wx (GD, GTK, PS, and Template are
already updated).

In a nutshell, the proliferation of defaultDPI and defaultFigSize
throughout several parts of the code and among the various backends is
now gone.  The only place where the defaults are set is in matlab.py
in the figure and savefig command.  This now makes it possible to
control the figsize and dpi from the matlab interface (which before
could only be done with the OO API.  

An unfortunate side effect is that the default appearance of figures
may now be different since I have changed the defaults (different
backends used to set their own defaults, so there was no standard).
Now I use a default fig size of 8,6 (from matlab) and dpi of 72.

Jeremy - what this means for you is some more changes.  Sorry to
present you with an ever changing target.  I've been working pretty
hard of late clearing up a lot of lingering issues.  Hopefully, we'll
stabilize soon....

- Changes to the matlab helpers API

  * _matlab_helpers.GcfBase is renamed by Gcf.  Backends no longer
    need to derive from this class.  Instead, they provide a factory
    function new_figure_manager(num, figsize, dpi).  The destroy
    method of the GcfDerived from the backends is moved to the derived
    FigureManager.  You'll want to connect the window destroy to the
    GCf.destroy method, which will forward the call to the
    FigureManager.

  * FigureManagerBase moved to backend_bases -- seemed like a better
    place for it.

  * Gcf.get_all_figwins renamed to Gcf.get_all_fig_managers

  * No default dpi or figsize arguments in the backends.

  * You'll need to change the backends.__init__ for wx to reflect the
    new API.

It was rather easy to port the existing backends and I don't think
you'll have much trouble with WX.  Note there is a SCREENSIZE
parameter in the backend_gtk and backend_gd which is a constant that
determines how many pixels there are per inch on the screen.  I use
this to convert from dpi (in which I assume a dpi of 72 == 1 inch) to
screen units.  In my tests where I created figures with a dpi of 72,
this resulted in accurate measures of figure sizes (holding a ruler up
to the screen).

Not sure this is perfect yet, but it seems to be a step in the right
direction, and the relative sizes of the fonts to the figure appear to
be better now -- previously too large in some backends, eg, GD.  There
is still a discrepancy between relative font sizes between the
backends (eg, GTK versus PS) which may have to do with the font dpi
issue (75 versus 100 dpi fonts under X11) but am not sure.  In any
case, I think the CVS changes are step in the right direction

Let me know if this is clear ....

JDH