On Fri, Feb 26, 2010 at 5:14 PM, brianjpetersen
<brianjpeter...@gmail.com> wrote:
>
> Hi All,
>
> I'm a new matplotlib user on a Windows XP machine running mpl0.99.0 under
> Python 2.5. I'm using the default rc file.
>
> While reading through the excellent matplotlib "how-to" tutorial
> (http://matplotlib.sourceforge.net/faq/howto_faq.html), I came across two
> useful scripts: one to save a figure with a transparent background, and one
> to resize axes automatically so that labels aren't cut off. I was able to
> run both these examples given on the "how-to" successfully.
>
> However, I ran into trouble when trying to combine them as follows:
>
> =====
>
> import matplotlib.pyplot as plt
> import matplotlib.transforms as mtransforms
>
> fig = plt.figure()
> ax = fig.add_subplot(111)
> ax.plot(range(10))
> ax.set_yticks((2,5,7))
> labels = ax.set_yticklabels(('really, really, really', 'long', 'labels'))
>
> def on_draw(event):
> bboxes = []
> for label in labels:
> bbox = label.get_window_extent()
> # the figure transform goes from relative coords->pixels and we
> # want the inverse of that
> bboxi = bbox.inverse_transformed(fig.transFigure)
> bboxes.append(bboxi)
>
> # this is the bbox that bounds all the bboxes, again in relative
> # figure coords
> bbox = mtransforms.Bbox.union(bboxes)
> if fig.subplotpars.left < bbox.width:
> # we need to move it over
> fig.subplots_adjust(left=1.1*bbox.width) # pad a little
> fig.canvas.draw()
>
> return False
>
> fig.canvas.mpl_connect('draw_event', on_draw)
>
> plt.savefig('test.png', transparent=True)
>
> =====
>
> In this case, the saved png file is transparent, but the original set of
> axes, labels, and plot are visible as well (basically, I have two identical
> plots shifted over one another on a transparent background).
>
> Is there a way to suppress the original output (something akin to
> "fig.canvas.erase()" or "fig.canvas.clear()", but I can't seem to figure it
> out) so that the output png only shows the shifted axes and not both sets?
Interesting! That one really surprised me. It turns out mpl is not
clearing the pixel buffer from the previous draw command. Normally
you don't see this because the call to draw the figure.patch blanks
out the pixel buffer with the background color, but since your figure
patch is transparent you can see the legacy. A call to
renderer.clear() before drawing again will erase the old image
(perhaps we should be doing this by default?)
import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import matplotlib.transforms as mtransforms
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(range(10))
ax.set_yticks((2,5,7))
labels = ax.set_yticklabels(('really, really, really', 'long', 'labels'))
def on_draw(event):
bboxes = []
for label in labels:
bbox = label.get_window_extent()
# the figure transform goes from relative coords->pixels and we
# want the inverse of that
bboxi = bbox.inverse_transformed(fig.transFigure)
bboxes.append(bboxi)
# this is the bbox that bounds all the bboxes, again in relative
# figure coords
bbox = mtransforms.Bbox.union(bboxes)
if fig.subplotpars.left < bbox.width:
# we need to move it over
fig.subplots_adjust(left=1.1*bbox.width) # pad a little
fig.canvas.get_renderer().clear()
fig.canvas.draw()
return False
fig.canvas.mpl_connect('draw_event', on_draw)
plt.savefig('test.png', transparent=True)
JDH
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