:-object balllook : [bcilib].

     var url = './yt/yt-with-ball.wrl'.
     var count = 0.
     var timelimit = 500.
     var avatarHeight = 1.5.

	main:-
		text_area(BrowserStream),
		set_output(BrowserStream),
		format('look-at-ball  example is running ...~n'),
		format('Loading the humaniod from ~w~n', [url]),
		format('Please wait ...~n'),
		loadURL(url),
		format('you can run this example until the counter is ~w~n',[timelimit]),
		format('Use the mouse to move around the ball~n'),
		sleep(6000),
		play(hanim_HumanoidRoot,ball,timelimit),
		true.

play(Agent,Object,Time):-
	count := 0,
	repeat,
		look_at_ballEx(Agent,Object),
		format('the counter is ~w.~n',[count]),
		++count,
	count > Time,
	!.

look_at_ballEx(Player,Ball) :-
	getSFVec3f(Player,translation, X,Y,Z),
	getPosition(Ball, X1,Y1,Z1),
	getPlayerHead(Player,PlayerHead),
	X =\= X1,
	!,
	Xdif is X-X1,
	Ydif is Y1-(Y + avatarHeight),
	Zdif is Z1-Z,
	Distance is sqrt(Xdif*Xdif+Zdif*Zdif),
	Ry is atan(Ydif/Distance),
	setRotation(PlayerHead,-1.0, 0.0, 0.0, Ry),
	R is atan(Zdif/Xdif) - sign(Xdif)*1.571,
	setRotation(Player,0.0, 1.0, 0.0, R).

look_at_ballEx(Player,Ball) :-
	getSFVec3f(Player,translation, _X,Y,Z),
	getPosition(Ball, _X1,Y1,Z1),
	getPlayerHead(Player,PlayerHead),
	Z =\= Z1,
	!,
	Ydif is Y1-(Y + avatarHeight),
	Zdif is Z1-Z,
	Ry is atan(Ydif/Zdif),
	setRotation(PlayerHead,-1.0, 0.0, 0.0, Ry).


look_at_ballEx(_,_):-!.

getPlayerHead(hanim_HumanoidRoot,hanim_skullbase):-!.

getPlayerHead(_,_):-
	format('unknown body part~n').



:-end_object balllook.