Class SphereWindow

         object --+            
                  |            
ClassWithParameters --+        
                      |        
               Stimulus --+    
                          |    
     LuminanceGratingCommon --+
                              |
                             SphereWindow

This draws an opaque sphere with a single window in it.

This is useful when you need to have a viewport on a 3D scene.

Note that the bit depth of the alpha component of the framebuffer
is important for producing smooth transitions in color.

Parameters
==========
bit_depth                     -- precision with which grating is calculated and sent to OpenGL (UnsignedInteger)
                                 Inherited from VisionEgg.Gratings.LuminanceGratingCommon
                                 Default: 8
num_s_samples                 -- (UnsignedInteger)
                                 Default: 512
num_t_samples                 -- (UnsignedInteger)
                                 Default: 512
on                            -- (Boolean)
                                 Default: True
opaque_color                  -- (Sequence4 of Real)
                                 Default: (0.5, 0.5, 0.5, 0.0)
radius                        -- (Real)
                                 Default: 1.0
slices                        -- (UnsignedInteger)
                                 Default: 30
stacks                        -- (UnsignedInteger)
                                 Default: 30
window_center_azimuth         -- (Real)
                                 Default: 0.0
window_center_elevation       -- (Real)
                                 Default: 0.0
window_shape                  -- (String)
                                 Default: gaussian
window_shape_radius_parameter -- (Real)
                                 Default: 36.0

Instantiate and get ready to draw.

Set parameter values and create anything needed to draw the
stimulus including OpenGL state variables such display lists
and texture objects.

Redraw the scene on every frame.