Class SinGrating2D

         object --+            
                  |            
ClassWithParameters --+        
                      |        
               Stimulus --+    
                          |    
     LuminanceGratingCommon --+
                              |
                             SinGrating2D

Sine wave grating stimulus

This is a general-purpose, realtime sine-wave luminace grating
generator. To acheive an arbitrary orientation, this class rotates
a textured quad.  To draw a grating with sides that always remain
horizontal and vertical, draw a large grating in a small viewport.
(The viewport will clip anything beyond its edges.)

Parameters
==========
anchor                      -- specifies how position parameter is interpreted (String)
                               Default: center
bit_depth                   -- precision with which grating is calculated and sent to OpenGL (UnsignedInteger)
                               Inherited from LuminanceGratingCommon
                               Default: 8
color1                      -- (AnyOf(Sequence3 of Real or Sequence4 of Real))
                               Default: (1.0, 1.0, 1.0)
color2                      -- optional color with which to perform interpolation with color1 in RGB space (AnyOf(Sequence3 of Real or Sequence4 of Real))
                               Default: (determined at instantiation)
contrast                    -- (Real)
                               Default: 1.0
depth                       -- (Real)
                               Default: (determined at instantiation)
ignore_time                 -- (Boolean)
                               Default: False
mask                        -- optional masking function (Instance of <class 'VisionEgg.Textures.Mask2D'>)
                               Default: (determined at instantiation)
max_alpha                   -- (Real)
                               Default: 1.0
num_samples                 -- (UnsignedInteger)
                               Default: 512
on                          -- draw stimulus? (Boolean)
                               Default: True
orientation                 -- (Real)
                               Default: 0.0
pedestal                    -- (Real)
                               Default: 0.5
phase_at_t0                 -- (Real)
                               Default: 0.0
position                    -- (units: eye coordinates) (Sequence2 of Real)
                               Default: (320.0, 240.0)
recalculate_phase_tolerance -- (Real)
                               Default: (determined at instantiation)
size                        -- (Sequence2 of Real)
                               Default: (640.0, 480.0)
spatial_freq                -- (Real)
                               Default: 0.0078125
t0_time_sec_absolute        -- (Real)
                               Default: (determined at instantiation)
temporal_freq_hz            -- (Real)
                               Default: 5.0

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.

Draw the stimulus. (Called by Viewport instance.)

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