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

991 111ObjectivesAfter reading Chapter 1(/) you should be able to (if fo rced):• Draw a vector diagram fo r a figure.• List and encode the vectors from the diagram.• Group the vector codes into bytes.• Develop a shape table from one or more shapes.• Save and recover a shape table from disk or tape.• Use the shape commands to plot, scale, and rotate a shape.In this chapter you will investigate the properties of Apple shapes andshape tables. The term "shape" is used here in a very specific sense. Fromthe programmer's point of view, a shape could be almost any figure-aspaceship, frog, alien, and so on-but to the computer a shape is a set ofhighly formatted data which lets the machine produce a display on thescreen.Though using a shape can cost you extra time at the outset, in practice itmakes drawing and animating figures much faster and simpler than thetechniq ues we have discussed in the previous two chapters. Shapes mayalso be used to simulate text on the Hi-Res screen.After you digitize a: figure to create a shape, that shape can be plotted onthe screen as a unit so that you no longer need to concern yourself withcalculating the necessary addresses, nor the values to POKE. APPLESOFTtakes care of all those grubby little details, and also plots the shape fasterthan you could if you used the READ and POKE technique discussed inearlier chapters.