The RasInfo structure provides information to the system about the location of the BitMap as well as the positioning of the display area as a window against a larger drawing area. Use the following steps to prepare the RasInfo structure: /* Initialize the RasInfos. */ rasInfo.BitMap = &bitMap; /* Attach the corresponding BitMap. */ rasInfo.RxOffset = 0; /* Align upper left corners of display */ rasInfo.RyOffset = 0; /* with upper left corner of drawing area.*/ rasInfo.Next = NULL; /* for a single playfield display, there * is only one RasInfo structure present */ The system may be made to reinterpret the RxOffset and RyOffset values in a ViewPort's RasInfo structure by calling ScrollVPort() with the address of the ViewPort. Changing one or both offsets and calling ScrollVPort() has the effect of scrolling the ViewPort.