function ImageAnim(object_id,height,frames,delay)
    {
    this.style = getStyleObject(object_id);
    this.frame = 0;
    this.frames= frames;
    this.height= height;
    this.d     = 0;

    addTimer(this,delay);

    //functions
    this.play=ImageAnim_play;
    this.playRewind=ImageAnim_playRewind;
    this.tick=ImageAnim_tick;
    }

function ImageAnim_tick()
    {
    if (this.d!=0)
        {
        this.frame = this.frame+this.d;
        if (this.frame<=0 || this.frame>=this.frames-1)
            this.d=0;
            
        y=-this.frame*this.height;
        this.style.top = y+"px";
        }
    else
        this.d=0;
    }

function ImageAnim_play()
    {
    if (this.frame<this.frames-1)
        this.d = 1;
    else
        this.d = 0;
    }

function ImageAnim_playRewind()
    {
    if (this.frame>0)
        this.d = -1;
    else
        this.d = 0;
    }