add callbacks for mouse movement and mouse clicking

ffi/glfw-input.sml

@@ -0,0 +1,24 @@
+structure Input =
+struct
+  type window = MLton.Pointer.t
+
+  (* Export function to C. *)
+  val exportMouseMoveCallback =
+    _export "mltonMouseMoveCallback" public : (int * int -> unit) -> unit;
+
+  (* Import function to set callback for GLFW. *)
+  val setMouseMoveCallback = _import "setMouseMoveCallback" public reentrant : window -> unit;
+
+  val exportMouseClickCallback =
+    _export "mltonMouseClickCallback" public : (int * int -> unit) -> unit;
+
+  val setMouseClickCallback = _import "setMouseClickCallback" public reentrant : window -> unit;
+
+  (* Constants for mouse input. *)
+  val (MOUSE_PRESSED, _) =
+    _symbol "MOUSE_PRESSED" public : ( unit -> int ) * ( int -> unit );
+  val (MOUSE_RELEASED, _) =
+    _symbol "MOUSE_RELEASED" public : ( unit -> int ) * ( int -> unit );
+  val (LEFT_MOUSE_BUTTON, _) =
+    _symbol "LEFT_MOUSE_BUTTON" public : ( unit -> int ) * ( int -> unit );
+end