Re: [Matplotlib-users] Getting the size of Text objects

[Chris B. <Chr...@no...>]

John,

Thanks for the reply. Sorry for the delay, I've been off line for a few 
days.

John Hunter wrote:
>>>>>>"Chris" == Chris Barker <Chr...@no...> writes:

>     Chris> Hi all, Is there a way to get the size of a text object?

> Do you mean the width and height
> in points?

At this point, points. The other option is figure coordinates. The 
problem at hand is that we're generating a figure that has some fairly 
large labels on the Y axis, so we're having to do the layout of subplots 
ourselves. We've got it looking OK with trial and error, but if we 
change a label, it might not layout right anymore, so I thought it would 
be helpful to be able to check the sizes of things to do it automagically.

Besides, aren't there methods to convert between the various coord. 
systems anyway?

> but could be screwed up by a figure resize.

Yeah, it would , but right now I'm working with the AGG backend, so I 
can stick with one figure size.

> FYI, this is an issue that crops up a lot and is vexing.  What one
> would like to be able to do is use a layout engine and say, place
> object one above and to the right of object 2 with a pad of 2 points.

Yes, that would be nice. In fact, I've been planning to do exactly that 
for my wxFloatCanvas. It's easier there because I've only got wx as a 
back end, but still a bit tricky. One thing I've done to help is simply 
declare that I'm always assuming 72dpi, rather than trying to use the 
system's idea of the display resolution. This has helped keep results 
consistent across systems. I have had to re-scale text, however.

> The text instance can give you its bounding box in display if you pass
> it the backend renderer -- this is required because the width and
> height can be backend dependent.  I suppose you are using OO agg based
> on your previous posts.

Mostly, it's a mix as I'm working with someone else and most of the 
examples are in the pylab interface.

> One problem with the current design that is
> that the agg canvas doesn't generate it's renderer until draw time
> (with caching), but you need access to the renderer before draw time
> for layout that depends on text.

Right. So, do any of the default layout's take text into account 
(subplot, for example?)

 > If we move this logic to a
> get_renderer method, you can use it at draw time.  I'll attach a
> replacement backend_agg.FigureCanvasAgg class to support this below
> 
>     from matplotlib.figure import Figure
>     from matplotlib.backends.backend_agg import FigureCanvasAgg
> 
>     fig = Figure()
>     canvas = FigureCanvasAgg(fig)

Didn't you add canvas as a Figure() attribute to support the new 
Figure.savefig() method? (added for me, such service!)

>     renderer = canvas.get_renderer()
>     ax = fig.add_subplot(111)
>     ax.plot([1,2,3])
>     t = ax.text(1,2,'hi mom')
>     bbox =  t.get_window_extent(renderer)
>     print 'display', bbox.get_bounds()  #l,b,w,h
> 
>     # get the axes data coords bbox of this display bounding box
>     from matplotlib.transforms import inverse_transform_bbox
>     axbox = inverse_transform_bbox(ax.transData, bbox)
> 
>     print 'data coords', axbox.get_bounds()
> 
>     fig.savefig('test')

Thanks for this example. I hope I"ll get a chance to play with this 
soon. My schedule is a nightmare for a while.

thanks,

-Chris



-- 
Christopher Barker, Ph.D.
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