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

8Hi-Res GraphicsObjectivesAfter reading Chapter 8 you should be able to:• Calculate the address for any byte on the Hi-Res screen.• Calculate the value needed to produce a give n dot pattern in a byte,and use both BASIC and Monitor to place that value in Hi-Res screenmemory.• Design, digitize, and display simple figures in Hi-Res.A large percentage of the commercial software written fo r persona I computerstoday uses Hi-Res graphics. Games, graphing packages, draftingdesign programs, several word processors, and even some of the alternatelanguages (for example, PILOT and LOGO) use the Hi-Res graphics screenfor video output. Reflecting the pre-eminence of Hi-Res, the remainder ofthis book will be almost entirely devoted to various methods of controllingthis mode of output.Hi-Res gains an advantage over Low-Res because it lets you have individualcontrol of each dot on the screen; there are 280 such dots horizontallyacross the screen and up to 192 dots vertically. The appearance of animage on the video screen is greatly affected by the degree of resolution(the number of dots per inch) in which it is drawn. In Chapter 6 you sawhow the figure of the apple suffered when it was blocked out for Low-Reswhich has only four "dots" per inch. The Hi-Res dots are seven timessmaller than the Low-Res blocks, so the Hi-Res mode produces figures thatlook much better; but as with any improvement, there is a price to pay.65