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

164 APPLE II COMPUTER GRAPHICStogether, the scanning routine will sometimes decide that the wrong onehas been shot.The other method of dealing with extraneous objects is to use both Hi­Res screens. One screen is displayed with all the missiles, targets and otherjunk on it, while the other has only the missiles and targets on it, and is notdisplayed. The collision detect routine can then check the second screenand not even worry about the extra figures! In some applications the extratime needed to process two screens is offset by not having to decide whatyou ran rnto.In Summary ....That about wraps it up. Hopefully this book has shed some light on waysto make Apple graphics do what you want them to, and how many of thegames achieve their effects.So now you have it-the tricks of the animation trade. The ideas presentedhere are the most common and effective techniques currently usedwith the APPLE II. Programming personal computers is a creative and fastpacedsport. It is limited only by the programmer's imagination, so we canexpect that before too long there will be new, improved methods-that's(programming) life! However, the animation techniques you have learnedhere will still be usefu l, and the skills gained will help you to understandand implement the new approaches.VocabularyBox methodCollision flagContact methodExercises1. Use the table which contains the apple shape (from Chapter 1 l/J) toanimate two apples on the screen, each under control of one of thepaddles. (If you do not have paddles, control the apple's movementwith the keyboard.) Write a collision detect routine using either thebox or contact method to determine when the two shapes collide.2. Use the program from Chapter 13 (Listing 13-2), which moves thebyte-move line across the screen, and draw the spider shape in itspath. Write a routine to signal when they contact.3. Write a computer game and make a million bucks.