Add initial prototype.

4-high/gel/applet/demo/sprite/drop_ball_on_box/drop_ball_on_box.gpr

@@ -0,0 +1,22 @@
+with
+     "gel",
+     "lace_shared";
+
+project Drop_Ball_On_Box
+is
+   for Object_Dir use "build";
+   for Exec_Dir   use ".";
+   for Main       use ("launch_drop_ball_on_box.adb");
+   for Languages  use ("Ada");
+
+   package Ide      renames Lace_shared.Ide;
+   package Builder  renames Lace_shared.Builder;
+   package Compiler renames Lace_shared.Compiler;
+   package Binder   renames Lace_shared.Binder;
+
+   package Linker
+   is
+      for Linker_Options use ("-g", "-lGL", "-lGLU", "-lglut", "-lSDL2");   
+   end Linker;
+
+end Drop_Ball_On_Box;

4-high/gel/applet/demo/sprite/drop_ball_on_box/launch_drop_ball_on_box.adb

@@ -0,0 +1,76 @@
+with
+     gel.Window.setup,
+     gel.Applet.gui_world,
+     gel.Forge,
+     gel.Sprite,
+     gel.World,
+     gel.Camera,
+
+     Physics,
+
+     ada.Text_IO,
+     ada.Exceptions;
+
+pragma unreferenced (gel.Window.setup);
+
+
+procedure launch_drop_Ball_on_Box
+--
+--  Drops a ball onto a box 'terrain'.
+--
+is
+   use gel.Applet,
+       gel.Applet.gui_world,
+       Ada.Text_IO;
+
+   the_Applet : gel.Applet.gui_world.view := gel.Forge.new_gui_Applet ("drop Ball on Box",
+                                                                       space_Kind => physics.Bullet);
+
+   function gui_World return gel.World.view
+   is
+   begin
+      return the_Applet.World (gui_world_Id);
+   end gui_World;
+
+
+   function gui_Camera return gel.Camera.view
+   is
+   begin
+      return the_Applet.Camera (gui_world_Id,
+                                gui_camera_Id);
+   end gui_Camera;
+
+
+   the_Ball : constant gel.Sprite.view := gel.Forge.new_ball_Sprite (gui_World);
+   the_Box  : constant gel.Sprite.view := gel.Forge.new_box_Sprite  (gui_World,
+                                                                     Mass => 0.0,
+                                                                     Size => [20.0, 1.0, 20.0]);
+begin
+   new_Line;
+   put_Line ("Use arrow keys and PgUp/PgDn to move the camera.");
+   new_Line;
+
+   gui_Camera.Site_is ([0.0, 2.0, 20.0]);                         -- Position the camera.
+   the_Applet.enable_simple_Dolly (in_World => gui_world_Id);     -- Enable user camera control via keyboards.
+
+   the_Ball.Site_is ([0.0, 10.0, 0.0]);
+
+   gui_World.Gravity_is ([0.0, -9.8, 0.0]);
+   gui_World.add (the_Ball);                                      -- Add ball.
+   gui_World.add (the_Box);                                       -- Add box.
+
+
+   while the_Applet.is_open
+   loop
+      the_Applet.freshen;     -- Handle any new events and update the screen.
+   end loop;
+
+   free (the_Applet);
+
+exception
+   when E : others =>
+      new_Line;
+      put_Line ("Unhandled exception in main task ...");
+      put_Line (ada.Exceptions.exception_Information (E));
+      new_Line;
+end launch_drop_Ball_on_Box;