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

74 APPLE II COMPUTER GRAPHICSFigure 8-5. Alien critter.[From The Artist by Warren Schwader, used with permission.]Whew! That seems like a lot of work just for a few dots!! As it happens,working up an entire figure is not much harder. However, your preliminaryplanning is extremely important when designing a figure in Hi-Reslet'sput together an alien critter as an example. Figure 8-5 shows a samplealien already drawn on graph paper. For simplicity, it is only seven dotswide and eight rows high so that it will fit within a single box of thememory map.The fi rst step is to calculate the value of each byte composing the alien.Figure 8-6 shows the dot patterns, the required bit patterns, and the correspondinghex and decimal values.DOT BIT HEX DECPATTERN PATTERN VALUE VALUE-------------------------------------·---------XXX-- !il!il!ill ll!il!il $1C 28-XXXXX- !il!illl lll!il $3D 61X--X--X !ill!il!il l!il!ill $49 73X--X--X !ill!il!il l!il!ill $49 73-XXXXX- !il!illl lll!il $3D 61--XXX-- !il!il!ill ll!il!il $1C 28-X---X- !il!ill!il !il!ill!il $22 34X-----X 0100 0001 $41 65Figure 8-6. Alien translation.The extra zero has been placed to the left of each bit pattern to supplythe "missing" eighth bit. Calculating the values was not difficult at all.Now you need to calculate the addresses.