> From: Nie, Jinsuo [mailto:j...@bnl.gov]
> Sent: Tuesday, June 22, 2010 09:33
...
> I modified the path_editor.py example in order to make a line editor, as
> attached. The path_editor.py worked fine on Qt4Agg. However, in the
> line editor, the line was not draggable on the same backend.
...
The problem seems to stem from the line not being marked invalid when its
set_data method is called. This can be seen by modifying your
motion_notify_callback method as follows; I removed the previous print
statements and inserted a new one:
def motion_notify_callback(self, event):
'on mouse movement'
if not self.showverts: return
if self._ind is None: return
if event.inaxes is None: return
if event.button != 1: return
x,y = self.line.get_data()
x[self._ind] = event.xdata
y[self._ind] = event.ydata
self.line.set_data(x, y)
print self.line._invalid
self.canvas.restore_region(self.background)
self.ax.draw_artist(self.line)
self.canvas.blit(self.ax.bbox)
The x returned by get_data is the same object as line._xorig (a private
attribute of the line object), so the changes you make to elements of x also
apply to _xorig. Then, set_data compares the incoming x with _xorig, sees
that they are the same object, and doesn't set the _invalid attribute to True.
With _invalid still False, the line is not redrawn.
I tested on Windows 7 with matplotlib 0.99.1 (and saw the same behavior you
did). The relevant code in matplotlib's lines.py was changed in revision 8054
(if I'm interpreting correctly), and that's why John saw the animation using
more recent matplotlib code. I checked the last released version (0.99.3) and
found the same code for set_data as in 0.99.1, so updating to 0.99.3 won't
help.
However, I see two alternative easy solutions. (1) After calling
self.line.set_data, call self.line.recache, which is what would happen
automatically if the _invalid attribute were True. (2) Call set_data with
different objects than the ones you received from get_data. For example:
vertices = zip(*self.line.get_data())
vertices[self._ind] = event.xdata, event.ydata
self.line.set_data(zip(*vertices))
The set_data method will then set _invalid to True, enabling the line to be
redrawn.
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