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From: Michael Droettboom <mdroe@st...>  20090126 14:41:08

Support for handling NaNs in curves is now on the branch and trunk. While this solves the infinite recursion problem, it still may be better in your specific case to use a CirclePolygon. All my fix does is remove an entire bezier curve when any of its elements are nonfinite  so we're talking an entire eighthwedge at least here. By using CirclePolygon, the amount of removal could be much less. Mike Michael Droettboom wrote: > At one point in history, the Agg backend would not do NaN removal on > paths with curves  but it looks like that's been inadvertently lost, > probably in all the shuffling wrt simplification that went on, since > simplification has similar restrictions. So at present, we have > problems because it's passing curves with too few points to Agg, since > it removes points with NaNs, but not necessarily the entire curve > segment. In any case, even passing the vertices asis (without NaNs > removed) to Agg still results in an infinite loop. > > The "real" fix, IMO, is to make the NaNhandling code aware of curves, > which requires doing a lookahead. That is  if a curve segment has > any NaNs at all, remove the entire curve segment. I've thought about > this for a bit, but now here's some impetus to finally implement it. :) > > Mike > > John Hunter wrote: > >> On Fri, Jan 23, 2009 at 2:06 PM, Michael Hearne <mhearne@...> wrote: >> >> >>> I have discovered, from the mailing list, the easy way to draw a circle >>> in linear space: >>> ...snip >>> cx = 700 >>> cy = 700 >>> r = 1000 >>> >>> xmin = cx  r >>> xmax = cx + r >>> ymin = cy  r >>> ymax = cy + r >>> >>> cir = Circle( (cx,cx), radius=r,facecolor='w',edgecolor='b') >>> a = gca() >>> a.add_patch(cir) >>> >>> axis([xmin,xmax,ymin,ymax]) >>> axis('equal') >>> >>> How can I plot a circle in log space? >>> >>> >> The problem is that your circle has negative vertices since cxr<0 and >> cyr<0. When this happens, mpl is transforming the vertices with log >> coordinates and getting nans, as it should. The problem is that these >> nan vertices are getting passed to the agg backend, and when the >> vertex type is curve4, as it is for a circle, agg gets stuck in an >> infinite recursion in the spline code. I suspect this is because the >> recursion expects the comparison operator on the vertices to be well >> behaved, but it is not in the presence of nans. The function in >> question is agg_curve.cpp curve4_div::recursive_bezier. There is a >> "maximum recursion limit" in that function, but for some reason I >> don't understand, it is not breaking out of the function. >> >> I committed a simple "fix" to the branch and the trunk to simply drop >> any patch where any of the vertices are nans >> >> if not np.isnan(tpath.vertices).any(): >> renderer.draw_path(gc, tpath, affine, rgbFace) >> >> We might be able to do better than this  is there a well defined way >> to deal with patches where any of the transformed vertices are nans? >> For simple polygons (no splines vertices), we could plot the polygon >> with all the nan containing vertices removed, though in some cases >> this could be a strange object  this appears to be what was >> happening by default with CirclePolygon with negative vertices but I >> think this was mostly fortuitous that agg dealt with the nans >> gracefully in this case. But for patches containing curve vertices, >> this seems like a bad idea, since simply dropping vertices from a >> spline curve is not defined. >> >> I'm including below some sample code that shows the bug on Agg >> >> JDH >> >> import matplotlib >> matplotlib.use('Agg') >> >> import matplotlib.pyplot as plt >> import matplotlib.patches as patches >> cx = 700 >> cy = 700 >> r = 1000 >> >> fig = plt.figure() >> ax = fig.add_subplot(111) >> >> #cir = patches.CirclePolygon( (cx,cy), radius=r,facecolor='w',edgecolor='b') >> cir = patches.Circle( (cx,cy), radius=r,facecolor='w',edgecolor='b') >> ax.add_patch(cir) >> ax.set_yscale('log') >> fig.savefig('test') >> plt.show() >> >> > >  Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA 