Class AzElGrid

         object --+        
                  |        
ClassWithParameters --+    
                      |    
               Stimulus --+
                          |
                         AzElGrid

Spherical grid of iso-azimuth and iso-elevation lines.

Parameters
==========
anti_aliasing    -- (Boolean)
                    Default: True
center_azimuth   -- (Real)
                    Default: 0.0
center_elevation -- (Real)
                    Default: 0.0
major_line_color -- (AnyOf(Sequence3 of Real or Sequence4 of Real))
                    Default: (0.0, 0.0, 0.0)
major_line_width -- (Real)
                    Default: 2.0
minor_line_color -- (AnyOf(Sequence3 of Real or Sequence4 of Real))
                    Default: (0.0, 0.0, 1.0)
minor_line_width -- (Real)
                    Default: 1.0
my_viewport      -- (Instance of <class 'VisionEgg.Core.Viewport'>)
                    Default: (determined at instantiation)
on               -- (Boolean)
                    Default: True
text_offset      -- (Sequence2 of Real)
                    Default: (3, -2)

Constant Parameters
===================
az_major_spacing       -- (Real)
                          Default: 30.0
az_minor_spacing       -- (Real)
                          Default: 10.0
el_major_spacing       -- (Real)
                          Default: 30.0
el_minor_spacing       -- (Real)
                          Default: 10.0
font_size              -- (UnsignedInteger)
                          Default: 24
num_samples_per_circle -- (UnsignedInteger)
                          Default: 100
radius                 -- (Real)
                          Default: 1.0
text_anchor            -- (String)
                          Default: lowerleft
text_color             -- (AnyOf(Sequence3 of Real or Sequence4 of Real))
                          Default: (0.0, 0.0, 0.0)
use_text               -- (Boolean)
                          Default: True

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.

Draw the stimulus. (Called by Viewport instance.)

This method is called every frame.  This method actually
performs the OpenGL calls to draw the stimulus.