INTERFACE AnimateVBT;
IMPORT VBT, Time, PaintOp;
IMPORT IntervalTimer;

Animated VBTs belong to a ``group'', so that all of the animations can change in a single lockstep.

Each animation must include at least one snapshot.

TYPE
  T <: Public;
  Private <: VBT.Leaf;
  Public =  Private OBJECT METHODS
    init(READONLY snapshots: ARRAY OF VBT.T;
                  group: Group := NIL;
                  bg: PaintOp.T := PaintOp.Bg): T;
    reset(position: CARDINAL := 0);
  END;
  (* The call "init" initializes an animated VBT
     given a set of snapshots, the animation
     group and the background. The call "reset"
     can be used to reset the animated vbt
     back to a particular location. If "group"
     is "NIL" then the animation gets its own
     unique group. *)

  Group <: GroupPublic;
  GroupPublic = IntervalTimer.T OBJECT METHODS
    init (duration: Time.T): Group;
    reset (position: CARDINAL := 0);
  END;
  (* Specialized groups may be created so that
     the animations of more than one animated VBT
     are synchronized. *)

PROCEDURE New(READONLY snapshots: ARRAY OF VBT.T;
              duration: Time.T := DefaultDuration): T;

Creates a new animated VBT, each frame of which will stay on the screen for at least the specified duration.

PROCEDURE Blink (ch: VBT.T; bg: PaintOp.T := PaintOp.Bg): T;

Blinks a VBT by screen by animating the set containing ch and a bg background.

PROCEDURE Stop(v: T);
PROCEDURE Go(v: T);

Stop and Go cause the animation to halt or continue.

CONST
  DefaultDuration = 1.0D0;

END AnimateVBT.