US Patent 7999806 Three-dimensional shape drawing device and three-dimensional shape drawing method

A device drawing a three-dimensional shape and including a high order bit comparing section comparing high order bits of a depth value retained by a high order Z-buffer memory with high order bits calculated by a calculation section. If these two sets of high order bits are the same, a low order bit comparing section compares low order bits retained by a low order Z-buffer memory with low order bits calculated by the calculation section. If a depth indicated by the high order bits calculated by the calculation section is shallow, the high order bits retained by the high order Z-buffer memory and the low order bits retained by the low order Z-buffer memory are updated. If a depth indicated by the low order bits calculated by the calculation section is shallow, the low order bits retained by the low order Z-buffer memory are updated.