FRAME BUFFER

PURPOSE:To make a combined display which uses plural frame buffers by constituting a frame buffer which outputs both a Z value showing depth information and an I value showing image information at the same time. CONSTITUTION:A Z value and an I value regarding one pixel are handled as one piece of information, so when they are sent out to a Z merging part, both the values are transferred preferably at the same time. For the purpose, a Z buffer is composed of a video RAM similarly to an image buffer 12 and has a RAM port for inputting and outputting the Z value to and from a drawing/control part 10 and a SAM port for outputting the Z value to the Z merging part. For a frame buffer which is so constituted as to store both the Z value and I value in one video RAM chip, the Z value and I value are outputted alternately from the SAM port. Further, those outputs are received alternately by flip-flops of two systems and then the Z value and I value can be transferred separately to the Z merging part.