Add initial prototype.

3-mid/opengl/source/platform/glx/opengl-screen.ads

@@ -0,0 +1,18 @@
+package openGL.Screen
+--
+--  Models an openGL screen.
+--
+is
+
+   type Item is tagged limited private;
+
+
+
+private
+
+   type Item is tagged limited
+      record
+         null;
+      end record;
+
+end openGL.Screen;