Click and drag on red point B to move the yellow squares.[br]The squares are hinged around a rhombus.[br]As you move B, the rigid squares move around but stay the same size. The empty space changes shape as the squares move.[br]When the angle at B is 90˚ empty squares are formed.[br]When the angle at B is 0˚ or 180˚ a tiling of yellow squares is formed.