Re: [Matplotlib-users] clipping and linewidth/circle radius

[Michael D. <md...@st...>]

jas...@cr... wrote:
> I'm trying to deal nicely with the clipping that happens when, for 
> example, a line has data that is inside its clipping box, but the 
> linewidth forces part of the line to be drawn outside of the clipping 
> box.  This is visible on the spine placement demo at 
> http://matplotlib.sourceforge.net/examples/pylab_examples/spine_placement_demo.html, 
> for example (the clipping at the top and bottom of most of the sine 
> waves).  This has been brought up here (or on the -devel list) before, 
> and it was suggested to just set the clipping off, but that won't work 
> in my case because sometimes I want to use that clipping box to limit 
> the data shown.
>
> The best solution I can think of is to expand the clipping box by 
> padding it with the line width.  For something like a scatter plot, I 
> would also be okay with expanding the clipping box by padding by the max 
> radius of a circle in the circle collection.  However, I can't quite 
> figure out how to do this with the transform framework.  If I just pad 
> the clip box using the padded() method, it seems to make it a static 
> Bbox instead of a TransformedBbox, and my line disappears.  Can someone 
> help?
>   
Yeah -- that sounds rather painful.  We don't currently have a way to 
dynamically grow a bbox like this and have it updated on zooming/panning 
etc. I think what ultimately needs to happen is that clipping is made 
aware of the spine placement (which is a relatively new feature) and 
automatically deal with these small adjustments of the clipping box.  
I'm thinking of the Axes clip_box becoming something dynamically 
calculated based on the placement of the spines.  But I think it will be 
much harder to do it from the outside.  Of course, it's hard to say if 
this is the right thing to do in the general case -- we'll always end up 
clipping some marker or another if the limits of the axes are anything 
but the limits of the actual data.  Hmm... I'll have to think on this 
some more.
> Another option I thought of was separating out masking the data from 
> clipping the graphics.  I suppose if I could get the data for the line 
> and mask it to be within the clipbox, but then just set clipping off, I 
> would still have the benefit of clipping things that were way outside of 
> my bounding box, but letting things like an extra bit of linewidth 
> through.  However, this requires doing things like computing 
> intersections of the line and the bounding box so that I can insert an 
> extra point for the "end" of the line at the bounding box.  This gets 
> harder when the line is a spline or something like that.
>   
Do you care about panning and zooming, or are you just creating static 
plots?  If static, then you can just pass in a masked array as the data 
and all of these things should be handled automatically (with the 
exception of splines).  Something like:

In [1]: X = np.arange(0, np.pi * 2.0, 0.001)

In [3]: Y = np.sin(X)

In [4]: X = ma.masked_where(X > np.pi * 1.5, X)

In [5]: Y = ma.masked_where((Y < -0.5) | (Y > 0.5), Y)

In [6]: plot(X, Y)


Cheers,
Mike

-- 
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA