Patent US 5,249,264

An image display apparatus in which respective L-buffers each store a depth value of a position on a front boundary surface of a clipping region, while respective Z-buffers each store a depth value of a position on a back boundary surface of the clipping region. A depth value is generated at each position on an object to be displayed in connection with a pixel position on the screen and is compared with the corresponding depth values in the L- and Z-buffers. A determination of whether each position on the object to be displayed exists in the clipping area is made in accordance with the results of the comparison with the buffer contacts.