Add initial prototype.

3-mid/opengl/source/platform/glx/private/thin/glx-event.ads

@@ -0,0 +1,29 @@
+with
+     glx.BufferSwapComplete,
+     glx.PbufferClobberEvent;
+
+package glx.Event
+is
+   type long_Array   is array (C.size_t range <>) of aliased C.Long;
+
+   type Kind is (pBufferClobber,
+                 BufferSwapComplete,
+                 Pad);
+
+   type Item (Kind : Event.Kind := Event.Kind'First) is
+      record
+         case Kind is
+         when pBufferClobber     => pBufferClobber     : aliased glx.PBufferClobberEvent.item;
+         when BufferSwapComplete => BufferSwapComplete : aliased glx.BufferSwapComplete .item;
+         when Pad                => Pad                : aliased long_Array (0 .. 23);
+         end case;
+      end record
+   with unchecked_Union;
+
+   type Pointer         is access all Item;
+   type Pointer_Pointer is access all Pointer;
+
+   type Items    is array (C.size_t range <>) of aliased Item;
+   type Pointers is array (C.size_t range <>) of aliased Pointer;
+
+end glx.Event;