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?
Here is the example code I'm using. I don't know what to put in for the
???, which is all that I think I need.
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
ax.plot([0,1],[1,1],lw=20)
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
ax.set_ylim([0,1])
line=ax.lines[0]
# I still want clipping for things that are outside of the original clip
box+linewidth padding
# so I don't want to take off clipping; I guess it doesn't matter for
this example, but it does for
# more complicated examples.
#line.set_clip_on(False)
bb=line.get_clip_box()
# How can I pad bb so that it is padded by
linewidth/2*1.0/72*fig.dpi_scale_trans.transform_point([1,1]) dots?
padded_bb=???
line.set_clip_box(padded_bb)
fig.savefig('test.png')
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.
Thanks for being patient with me while I learn my way around
matplotlib's excellent transformation framework.
Jason
--
Jason Grout
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