Re: [matplotlib-devel] Change to aspect ratio handling

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

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:

    Eric> All, Motivated in part by an old patch (1233294) submitted
    Eric> to sourceforge by Nikolai Hlubek, I took a look at how
    Eric> aspect ratio is handled in mpl, and concluded it wasn't
    Eric> quite right:

Just a few quick comments since I haven't had a chance to look over
this in any detail.

    Eric> 1) The aspect='preserve' kwarg in image caused the image to
    Eric> retain its aspect ratio only with some resize events, not
    Eric> with all.  The implementation in the image.py code does not
    Eric> look right to me.



    Eric> Therefore I have reworked the aspect-handling code in
    Eric> axes.py, and I think it is working reasonably well.  Indeed,
    Eric> I don't see any remaining need for an "aspect" kwarg in
    Eric> image.py, and I would like to take it out unless someone
    Eric> raises an objection.

The aspect handling of images has been known to be broken from the
early days, but in those days we didn't even have aspect='equal'
functionality, and so adding preserved aspect ratio proved to
daunting.  Noone has revisited the issue (until now) since Mark Bakkar
finally (mostly) got proper aspect handling in the axes.  So your
observations are on target, and the image aspect handling is an
anachronism that everyone quickly learned to ignore.

    Eric>      def set_aspect(self, aspect='auto', fixLimits=None,
    Eric> aspect_adjusts='position'): """ aspect: 'auto' - automatic;
    Eric> fill position rectangle with data 'normal' - same as 'auto';
    Eric> deprecated 'equal' - same scaling from data to plot units
    Eric> for x and y A - a circle will be stretched such that the
    Eric> height is A times the width. aspect=1 is the same as
    Eric> aspect='equal'.

Mark Bakkar wrote most of the aspect handling for the axes, and so he
can response most intelligently to these changes.  You should send him
your original post since he may not be on this list.  He's CCd above.

    Eric> One question: is there an easy way to automatically trigger
    Eric> a redraw in an interactive backend (e.g. ipython with
    Eric> gtkagg) at the end of the set_aspect() method, for example?
    Eric> The way it works now is that one can make a plot, call the
    Eric> set_aspect() method on the resulting axes object, and the
    Eric> result will appear as soon as the window is manipulated with
    Eric> the mouse; but this manipulation is needed to trigger a
    Eric> redraw.

You should be able to do something like 

  if rcParams['interactive']:
     self.figure.canvas.draw()

where self is an Axes instance.  Untested, but I think it is valid
across backends.

Thanks for the submission -- I look forward to testing it.

JDH