by Darrell Aldrich
This is a brief description of the use of the color mask byte (Location 81210) for high re solution graphics in Apple Integer Basic.
This mask specifies an 8 bit pattern of plottable X coordinates, with the pattern repeating itself every eight coordinates, going from left to right. The bits in this byte represent the colors violet and green, alternately. (See Figure 1).
Suppose we want to mask off every other green bar on the screen as in Figure 2a, where “X” indicates a point we want masked off. Set up an 8 bit byte as in Figure 2b, with all masking bits =0 and all non-masking bits=l. Convert this value to decimal & Poke in decimal location 812.