Class Quadrilateral

      object --+    
               |    
common.Primitive --+
                   |
                  Quadrilateral

Class to draw a 3D quadrilateral 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.

Quadrilaterals should be added to a Group and 
drawing done via Group. 

Create Quadrilaterals and add them to a Group instance 
like in the following.

Example:

   # One big list
   verts =  [ 0.0, 0.0, 0.0,   0.0, 1.0, 0.0,   
              1.0, 1.0, 0.0,   1.0, 0.0, 0.0 ]
   my_quadrilateral1 = quadrilateral.Quadrilateral(vertices=verts,
                opacity=0.5, r=1.0, g=0.0, b=0.0)

   # A list of vertices (each vertex is a list of x, y, z)
   v1 = [0.0, 0.0, 0.0]
   v2 = [0.0, 1.0, 0.0]
   v3 = [1.0, 1.0, 0.0]
   v4 = [1.0, 0.0, 0.0]   
   my_quadrilateral2 = quadrilateral.Quadrilateral(
                vertices = [v1, v2, v3, v4],
                opacity=0.5, r=1.0, g=0.0, b=0.0)

   quadrilateral_group = quadrilateral.Group()
   quadrilateral_group.add(my_quadrilateral1)
   quadrilateral_group.add(my_quadrilateral2)

   # The draw invocation would likely be in a callback function
   quadrilateral_group.draw()

Constructor requires:

vertices: List of 12 values: x1, y1, z1 ... x4, y4, z4 OR
          list of 4 vertex lists [x, y, z], ..., [x, y, z]

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

Optional arguments:

opacity:  0.0 (invisible) through 1.0 (opaque)
               Defaults to 1.0
          
style:         LINE or FILL.  Default is FILL.