title: matplotlib: filling under line in 3d polar plot
body: <p>I'd like to plot a sine wave on a circle: that is, the circle is in the x,y-plane and the sine wave wraps around it perpendicular to that plane (sticking up the z-axis). I can do this, but when I try to fill the areas between the circle and the sine wave with a polygon (ie paint on the surface of the imaginary cylinder on which my sine wave lives), I can't get it quite right - matplotlib seems to XOR the regions that overlap in a view of the plot instead of giving me a view in which the ones in front occlude those behind.
  Here's the relevant bit of my code:</p>
  
  <pre><code>fig = plt.figure()
  ax = fig.gca(projection='3d')
  ax._axis3don = False
  theta = np.linspace(0., 2 * np.pi, 1000)
  r = 1.
  x = r * np.sin(theta)
  y = r * np.cos(theta)
  sinez = N * np.sin(theta * m)
  ax.plot(x, y, sinez, color='r')
  xv = np.append(x, x[::-1])
  yv = np.append(y, y[::-1])
  zv = np.append(sinez, np.zeros(n))
  verts = [zip(xv,yv,zrev),]
  poly = Poly3DCollection(verts, facecolors = [cc('r'), cc('b')],
                          edgecolor='None')
  poly.set_alpha(0.7)
  ax.add_collection3d(poly)
  </code></pre>
  
  <p>Here's what it looks like:
  <img src="https://i.stack.imgur.com/YNEaz.png" alt="enter image description here"></p>