williams-et-al-1983-apple-ii-computer-graphics

81gHi-Res ColorObjectivesAfter reading Chapter 9 you should be able to:• Design and display a Hi-Res color figure.• When given the location of a dot on the screen and a desired color,determine if that color can be displayed at that location, and if so,calculate the byte of memory which contains that dot and POKE the·appropriate value into that location.• Use dithering to generate colors other than the six basic Hi-Resshades.Good color is virtually a requirement for quality Hi-Res products; mostsoftware publishers will not touch a Hi-Res program unless its color effectsare clear, clean, and smooth. Color enhances the display by distinguishingthe diffe rent elements of a picture or graph, by adding life to a screen, andby making the output more attractive to the eye of the viewer. YourApple's hardware is designed to produce six colors, including black andwhite and, by a software process known as dithering, can be made todisplay upwards of twenty additional hues.Getti ng color on the Hi-Res screen is simple-almost too simple sinceany time you plot a single dot, it is always in color. The trick is to developthe right color in the right place. By now you should be familiar with theway Hi-Res memory is laid out, and how to use the memory map to fi ndyour way around. You also need some facility in translating desired dotpatterns into their corresponding bit patterns, and then into their hex ordecimal values. Another necessary item is either a color display, or a veryvivid imagination.