OberonCore

      VAR m: SET;x1, y1: INTEGER; isDown: BOOLEAN;
   BEGIN
      REPEAT
         host.Input(x1, y1, m, isDown);
         host.MarkRect(x1-rx, y1-ry, x1-rx+w, y1-ry+h, 0, Ports.dim50, Ports.show);      
         host.MarkRect(x1-rx, y1-ry, x1-rx+w, y1-ry+h, 0, Ports.dim50, Ports.hide);
      UNTIL ~isDown;

      shown := FALSE;
      REPEAT
         host.Input(x1, y1, m, isDown);
         b.l := x1 - rx; b.t := y1 - ry; b.r := x1 - rx + w; b.b := y1 - ry + h;
         moved := shown & ((b.l # old.l) OR (b.t # old.t) OR (b.r # old.r) OR (b.b # old.b));
         IF shown THEN host.MarkRect(old.l, old.t, old.r, old.b, 0, Ports.dim50, Ports.hide) END;
         IF isDown THEN host.MarkRect(b.l, b.t, b.r, b.b, 0, Ports.dim50, Ports.show);
            old := b; shown := TRUE
         END
      UNTIL ~isDown;