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

132 APPLE II COMPUTER GRAPHICSAs we draw the wedges of the pie, our progress around the circle isproportional to the amount of the data graphed so fa r. That is, if we areone-third of the way around the circle, then the accumulated amount ofdata already graphed is one-third of the total to be graphed. So, as we goaround, line 37© accumulates the graphed data in ACC, and line 38©calculates the fraction of a full rotation. (Remember, in radian measure6.28 represents a full rotation.)Line 39© draws the line from the center of the circle (14©,8©) to the pointon the circle at the correct rotation.Round It OutYou have seen several fairly powerfu l schemes fo r graphing. They all producea reasonable result on the screen, but what about getting a printoutof the graph? As with most any programming problem, where there's a willthere's a way, but the most practical solution lies in pri nter hardware.There are several items presently on the market which allow you to"dump" the Hi-Res screen to a matrix printer, such as "GRAFTRAX*" forEpson printers, or the "GRAPPLER**" interface which works for most dotmatrixmachines. If you have, or acquire such an item, it comes withinstructions for dumping the Hi-Res screen.The programs presented here are designed to let you plot your own datawith a minimum of modifications. After yeiu have used these routines for atime they will become clearer to you, and improvements will begin tosuggest themselves. Down that path lies hours of both creativity and frustration.Have fu n!VocabularyBar chartCircle graphLine graphPie chart*Graftrax is a trademark of Epson of America.**Grappler is a trademark of Microtech, Inc.