Use of Color Mask Byte in HIRES

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.

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About the Author

billm

A.P.P.L.E. Chairman of the Board and Club president — Bill worked for the founder, Val J. Golding and A.P.P.L.E. from 1981 to 1982. In 1999, he began archiving the materials which were distributed and sold by A.P.P.L.E.. That project led to the group that remained of A.P.P.L.E. Bill was involved in the financial industry in Tokyo and has over 20 major office infrastructure projects to his name. In March 2001, he retired to write books and to spend more time pursuing personal interests. As the president of the users group, Bill is in charge of distribution of Call-A.P.P.L.E. magazine as well as the organization of this web site. Bill currently resides in Tokyo, Japan and Shelton, Wa splitting time between the places.