This paper describes the realization of the multiwindow system, where the framed nonrectangular windows can be operated with a high speed. The body image (the image to be displayed inside the frame) and the frame image (the image to be displayed as the frame), which are stored on the multiport memory, are read out in parallel, being synchronized to the CRT scanning, By selecting pixelwise one of those images, the window image displayed in the window is generated as a framed image. The selection signal for this purpose is generated based on the window shape information stored in the dedicated memory.
The multiwindow image is generated by selecting the image to be displayed for each pixel position on CRT using a hardware, A distributed priority encoder is used as the hardware for this purpose. According to the result of construction and experiment, it is expected that the multiwindow system can realize a sufficiently high-speed operation from the practical viewpoint for the 1200 x 1000 CRT screen using the existing circuit technology.
