On Mon, Nov 2, 2009 at 11:51 PM, Jae-Joon Lee <lee.j.j...@gmail.com> wrote:
> On Mon, Nov 2, 2009 at 10:52 PM, David Sanders <dpsand...@gmail.com>
> wrote:
> > from pylab import *
> >
> > ion()
> >
> > N = 1000
> > pos = zeros((N,2))
> >
> > figure(figsize=(8,8))
> > points, = plot(pos[:,0], pos[:,1], ',')
> > axis([-20,20,-20,20])
> >
> > for t in range(1000):
> >
> > pos += uniform(-1,1,N*2).reshape(N,2)
> > points.set_data(pos[:,0].copy(), pos[:,1].copy())
> > draw()
>
> The Line2D object keeps the input data as a cache and only update it
> (recache) if the new data is different than the cached one.
> The problem in this particular case is that the cache is actually a
> *pos* itself. And modifying the pos in place, actually modify the
> cache in the Line2D object. Thus, set_data sees that the given data is
> identical to the cached one, and skip the recaching.
> I'm not sure what is the best approach here, and I defer the fix (or
> not) to others.
> Meanwhile, you can force the recaching with recache method. i.e., call
> points.recache() after set_data. You don't need to make a copy also.
> As a matter of fact, I think it will give you a best performance (but
> not tested) if you directly update the cached data and do not call
> set_data.
> Note that in this particular case, pos == cache, so you actually don't
> need to call get_data, but this is not a general case.
>
> posx, posy = points.get_data(orig=True)
>
> for t in range(100):
> dx, dy = uniform(-1,1,N*2).reshape(2, N) # note the change in the shape
> posx += dx
> posy += dy
> points.recache()
> draw()
>
>
Dear JJ,
Many thanks for your answer -- "points.recache()" is exactly what I was
looking for to make my animations work.
It seems to me that this must be a reasonably common question, but I could
not find it in the documentation.
Perhaps it could be added to the animation cookbook?
Thanks and best wishes,
David.
PS: Apologies for the late reply -- I was travelling with difficult internet
access.
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