function Drawable_is_visible(page_top, page_height) {
        var elem_top = get_elem_xy(this.elem)[1];
        var elem_height = this.elem.height;
        if (typeof (elem_height) != 'number') elem_height = 1;
        return ((elem_top + elem_height) >= page_top && elem_top <= (page_top + page_height));
      }
// page_height - the height of the visible region
the height of the visible region
the height of the visible region
function Drawable_is_visible(page_top, page_height) {
        var elem_top = get_elem_xy(this.elem)[1];
        var elem_height = this.elem.height;
        if (typeof (elem_height) != 'number') elem_height = 1;
        return ((elem_top + elem_height) >= page_top && elem_top <= (page_top + page_height));
      }
function Drawable_is_visible ( page_top , page_height ) { var elem_top = get_elem_xy ( this . elem ) [ 1 ] ; var elem_height = this . elem . height ; if ( typeof ( elem_height ) != 'number' ) elem_height = 1 ; return ( ( elem_top + elem_height ) >= page_top && elem_top <= ( page_top + page_height ) ) ; }
page_height - the height of the visible region
page_height - the height of the visible region