opengl.model: Add a lit and textured circle model.

3-mid/opengl/source/lean/model/opengl-model-circle.ads

@@ -0,0 +1,25 @@
+package openGL.Model.circle
+--
+--  Provides an abstract model of a circle.
+--
+is
+   type Item is abstract new Model.item with private;
+
+
+   -- Sites begin at 'middle right' and proceed in an anti-clockwise direction.
+   --
+   function vertex_Sites (Radius : in Real;
+                          Sides  : in Positive := 24) return Vector_2_array;
+
+
+private
+
+   type Item is abstract new Model.item with
+      record
+         Radius : Real := 1.0;
+         Sides  : Positive range 3 .. 360;
+      end record;
+
+   Normal : constant Vector_3 := [0.0, 0.0, 1.0];
+
+end openGL.Model.circle;