Class Sphere

      object --+        
               |        
common.Primitive --+    
                   |    
          SphereCore --+
                       |
                      Sphere

Class to draw a 3D sphere in OpenGL.  Will be drawn
in the current OpenGL drawable.  This includes the ability
to draw into Maestro's Workspace.  It just needs to be
the current drawable.


See doc string for __init__ for details on instantiation.

Spheres should be added to a SphereGroup and drawing done via
SphereGroup.  See SphereGroup documentation.

This class draws the sphere directly using OpenGL.

API Example
-----------
import schrodinger.maestro.maestro as maestro
import schrodinger.graphics3d.common as common
import schrodinger.graphics3d.sphere as sphere

sphere_grp = common.Group()
st = maestro.workspace_get()
for at in st.atom:
    sph = sphere.Sphere(
        x=at.x,
        y=at.y,
        z=at.z,
        radius=1.0,
        resolution=20,
        opacity=0.8,
        color='red'
    )
    # Add the primative to the container.
    sphere_grp.add(sph)

# Add the draw callback.
maestro.workspace_draw_function_add(sphere_grp.draw)

# Hide the markers.
sphere_grp.hide()

# Remove the markers and the callback.
sphere_grp.clear()
maestro.workspace_draw_function_remove(sphere_grp.draw)

Constructor requires:

x, y, z:  coordinate specifying center of sphere in Angstroms.

color:    One of:
            Color object
            Color name (string)
            Tuble of (R, G, B) (each 0.0-1.0)

radius:   radius of the sphere in Angstroms


Optional arguments:

opacity:  0.0 (transparent) through 1.0 (opaque)
               Defaults to 1.0
resolution:    4 to 50
               Defaults to 16