I want a line (Line2D) object to move with the current cursor position on several axes of a figure. The way I'm doing it now is to re-draw the whole figure each time the cursor moves, by calling
fig.canvas.draw()
My figure consists in 14 panels among which 10 has a line which must move with the cursor, and doing this is very long.
I was wondering how to update only the lines and not redrawing the whole thing.
So I've tried to use
ax.draw_artist(line)
but this crashes. Here is a small example :
fig,ax = subplots()
line = Line2D([0.3,0.3],[0.1,0.8])
ax.add_artist(line)
fig.canvas.draw()
#here I see the line on the figure ok
# I update the position of the line
line.set_xdata([0.6,0.8])
# now draw the line (this should add another one (*))
ax.draw_artist(line)
this last line causes the following error:
--------------------------------------------------------------------------- RuntimeError Traceback (most recent call last) in () ----> 1 ax.draw_artist(line)
/Users/Heimdall/anaconda/lib/python2.7/site-packages/matplotlib/axes.pyc in draw_artist(self, a) 2096 """ 2097 assert self._cachedRenderer is not None -> 2098 a.draw(self._cachedRenderer) 2099 2100 def redraw_in_frame(self):
/Users/Heimdall/anaconda/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs) 53 def draw_wrapper(artist, renderer, *args, **kwargs): 54 before(artist, renderer) ---> 55 draw(artist, renderer, *args, **kwargs) 56 after(artist, renderer) 57
/Users/Heimdall/anaconda/lib/python2.7/site-packages/matplotlib/lines.pyc in draw(self, renderer) 524 525 renderer.open_group('line2d', self.get_gid()) --> 526 gc = renderer.new_gc() 527 self._set_gc_clip(gc) 528
/Users/Heimdall/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.pyc in new_gc(self) 95 96 def new_gc(self): ---> 97 self.gc.save() 98 self.gc.set_hatch(None) 99 self.gc._alpha = 1.0
RuntimeError: CGContextRef is NULL
I'm not sure where this error comes from??
Also, I've seen that I was supposed to somehow save the canvas before the first line is drawn and restore it each time I re draw it, so only one line appears. I've seen this could be done with :
background = canvas.copy_from_bbox(ax.bbox)
and restore it with
canvas.restore_region(background)
however I have neither of these two methods in the object 'canvas'. Is this a problem with the MacOSX backend?
I have matplotlib 1.3.1 installed with the distribution anaconda on macOS 10.9.
also I've been told I could use :
fig.canvas.blit(line.clipbox)
to draw the line at its new position, but that does absolutely nothing.
