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

156 APPLE II COMPUTER GRAPHICSso may slow the animation since movement is always delayed until thenext vertical blanking interval. Having to wait for less than one-sixtieth of asecond may not seem like much to you, but to your Apple it is quite a longtime. We will just have to wait and see what new techniques are developedfor the Apple·lie.VocabularyExclusive OR (EOR)Partial ModificationPre-CalculationPre-ShiftVertical BlankingVertical Blanking Location (VBL)Exercises1. Suppose that a figure beginning at (2(/)(/), 19(/J) on the Hi-Res screentravels with a slope of one-half (moves up one and right two eachtime). Develop a table containing its X-Y coordinate pairs from itsorigin until it runs into the TOP of the screen. (In the course ofmoving it will contact the right side of the screen. At that time itshould begin to move up one and left two with each movement.)2. Use the table developed in Exercise 1 to animate the square from theshape table discussed in this chapter.3. Use partial mod ification to cycle through ten digits on the Hi-Resscreen.4. Create a shape table containing a rectangle, its horizontal and verticalpre-shifts, its two diagonal (up one, over one) pre-shifts, and the preshiftsrequired to move the rectangle up one, right two or up one, lefttwo. (Use a graphics editor if you own one!)5. Use each of the pre-shifts developed in Exercise 4 to move the rectangle.