reintroducing useful methods

spb/backends/matplotlib/renderers/arrow3d.py

@@ -23,6 +23,31 @@ def __init__(self, x, y, z, dx, dy, dz, *args, **kwargs):
         mpl_toolkits = import_module("mpl_toolkits")
         self.proj_transform = mpl_toolkits.mplot3d.proj3d.proj_transform
 
+    # NOTE: when looking at coverage results, draw() and do_3d_projection()
+    # appears to be unused.
+    # One might be inclined to removed them. Don't! Matplotlib probably
+    # executes these methods at visualization time, when the figure is actually
+    # shown on screen. They are not going to be executed when the figure is
+    # created.
+    def draw(self, renderer):
+        x1, y1, z1 = self._xyz
+        dx, dy, dz = self._dxdydz
+        x2, y2, z2 = (x1 + dx, y1 + dy, z1 + dz)
+
+        xs, ys, zs = self.proj_transform((x1, x2), (y1, y2), (z1, z2), self.axes.M)
+        self.set_positions((xs[0], ys[0]), (xs[1], ys[1]))
+        super().draw(renderer)
+
+    def do_3d_projection(self, renderer=None):
+        x1, y1, z1 = self._xyz
+        dx, dy, dz = self._dxdydz
+        x2, y2, z2 = (x1 + dx, y1 + dy, z1 + dz)
+
+        xs, ys, zs = self.proj_transform((x1, x2), (y1, y2), (z1, z2), self.axes.M)
+        self.set_positions((xs[0], ys[0]), (xs[1], ys[1]))
+
+        return np.min(zs)
+
 
 def _draw_arrow_3d(renderer, data):
     p, s = renderer.plot, renderer.series