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

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40 APPLE II COMPUTER GRAPHICSthe letter "A" without using a PRINT statement. It is similar in effect toListing 4-3, but uses no machine language subroutine.10 HOME20 FOR I = 1024 TO 204 730 POKE I ,193 : REM 193 IS "A"40 FOR J = 1 TO 30 :REM DELAY50 NEXT J60 NEXT I70 CALL 65338: REM BEEP SPEAKER80 GOTO 80Listing 6-1.After clearing the screen, the program proceeds to POKE the numericcode for "A" into every memory location from 1024 through 2047 ($400-$7FF), which is the range displayed on the Text/Low-Res screen. You willsee the screen fi ll with "A's"; the speaker will beep when the screen is fu ll.In order to regain control of your machine you will have to press.Try replacing the number 30 in line 40 with a diffe rent value. The higherthe number you select, the slower the screen will fi ll. Also try changing thevalue POKEd in line 30; fo r example, using a 1 instead of 193 will fi ll thescreen with inverse "A's".Notice that the screen fi lls in three separate pieces, even though theprogram fi lls memory sequentially. The fi rst line of A's appears at the top ofthe screen, the second appears almost a third of the way down the screen,and the third line appears roughly a third below the second. The fourthline fi lls under the fi rst, the fifth under the second, and so on until thescreen is fu ll. This three-part fi lling sequence is not just coincidence, but ismore of a curse which haunts anyone dealing with graphics. It makesdetermining the address of any location on the screen rather difficult. Thereason fo r the peculiar design of screen memory is tied up with the electronics,though in simple terms it was easier to wire the computer togetherthat way. As you can see, however, locating the proper address to match adesired position on the screen could turn into a problem.This problem is usually solved by the use of a memory map such as theone in Figure 6-1 .Finding Your WayTo use the map, fi rst locate the position that you want on the map, say thesecond row down and the third box from the right. The address of thatspace on the text screen is found by adding the row and column numberswhich are found to the left of the chosen box and directly above it, in this
CHAPTER 6-TEXT AND LOW-RES 41exam ple 1152 + 37 = 1189. The hex address is $48© + $25 = $4A5.(Remember: $8 + $2 = $A.)Example 1Use POKE to write "ACROSS" horizontally on the text screen, beginningin the third row and twenty-fi rst col umn. - - - - - - - - - - - - - - - - - - - - -s oo w N - OO w - s N - Ss - oo w s w s N N w s oo NS N OO S N S N OO S N S N OO S N 10II12131415161718192021222324252627282930313233343536373839$00$0 1$02$03$04$05$06$07$08$09$0A$0Bsoc$00$0E$0F$10Si l$12$13$14$15$16$17$18$19SIASIBSICSIDSIESIFS20S2 1S22S23S24S25$26$27Figure 6-1. Text/Low-Res memory map.(Used with permission of Apple Computer Corporation)
Page 3 and 4: APPLE IICOMPUTERGRAPHICSKen William
Page 5 and 6: Contents1 Introduction 12 Computer
Page 7 and 8: 1IntroductionThe level of graphics
Page 10 and 11: 4 APPLE II COMPUTER GRAPHICSmachine
Page 12 and 13: 6 APPLE II COMPUTER GRAPHICScompute
Page 14 and 15: 8 APPLE II COMPUTER GRAPHICSzeros i
Page 16 and 17: 10 APPLE II COMPUTER GRAPHICSthe sy
Page 18 and 19: •
Page 20 and 21: 14 APPLE II COMPUTER GRAPHICSdiffer
Page 22 and 23: 16 APPLE II COMPUTER GRAPHICSDOS ve
Page 24 and 25: 18 APPLE II COMPUTER GRAPHICSThe po
Page 27 and 28: 4APP LESO FTExtensionsObjectivesAft
Page 29 and 30: CHAPTER 4-APPLESOFT EXTENSIONS 23va
Page 31 and 32: CHAPTER 4-APPLESOFT EXTENSIONS 251
Page 35 and 36: Introducing -Diskette to Accompany
Page 39 and 40: 5Graphics Modes andSoft SwitchesObj
Page 41 and 42: CHAPTER 5-CRAPHIC MODES AND SOFT SW
Page 43 and 44: CHAPTER 5-GRAPHIC MODES AND SOFT SW
Page 45: CHAPTER 5-CRAPHIC MODES AND SOFT SW
Page 50 and 51: 42 APPLE II COMPUTER GRAPHICSSoluti
Page 52 and 53: 44 APPLE II COMPUTER GRAPHICSEach b
Page 54 and 55: ..46 APPLE II COMPUTER GRAPHICS[ b
Page 56 and 57: 48 APPLE II COMPUTER GRAPHICS3 PLOT
Page 58 and 59: 50 APPLE II COMPUTER GRAPHICSType t
Page 60 and 61: 52 APPLE II COMPUTER GRAPHICSVocabu
Page 62 and 63: 54 APPLE II COMPUTER GRAPHICScolor.
Page 64 and 65: 56 APPLE II COMPUTER GRAPHICSThis m
Page 66 and 67: 58 APPLE II COMPUTER GRAPHICSmuch l
Page 68 and 69: 60 APPLE II COMPUTER GRAPHICS70 POK
Page 70 and 71: 62 APPLE II COMPUTER GRAPHICS37- 85
Page 73 and 74: 8Hi-Res GraphicsObjectivesAfter rea
Page 75 and 76: CHAPTER 8-Hl-RES GRAPHICS 67When J
Page 77 and 78: C..: HAPTER 8-Hl-RES GRAPHICS 69Goi
Page 79 and 80: CHAPTER 8-Hl-RES GRAPHICS 71Row Add
Page 81 and 82: CHAPTER 8-Hl-RES GRAPHICS 73The fou
Page 83 and 84: CHAPTER 8-Hl-RES GRAPHICS 75The row
Page 85 and 86: CHAPTER 8-Hl-RES GRAPHICS 77Solutio
Page 87: CHAPTER 8-Hl-RES GRAPHICS 79b. XX-X
Page 90 and 91: 82 APPLE II COMPUTER GRAPHICSA Bit
Page 92 and 93: 84 -APPLE II COMPUTER GRAPHICSget t
Page 94 and 95: 86 APPLE II COMPUTER GRAPHICSDOTBIT
Page 96 and 97: 88 APPLE II COMPUTER GRAPHICSIn Fig
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90 APPLE II COMPUTER GRAPHICSblue a
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92 APPLE II COMPUTER GRAPHICSHEX HE
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94 APPLE II COMPUTER GRAPHICS50 HGR
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96 APPLE II COMPUTER GRAPHICSone of
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991 111ObjectivesAfter reading Chap
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CHAPTER 10-SHAPING UP 101A closed d
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CHAPTER 10-SHAPING UP 103In the fir
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CHAPTER 10-SHAPING UP 105( (J(J) ha
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CHAPTER 10-SHAPING UP 107as the com
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6 POKE 232,: POKE 233 ,37 REM8 REM
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CHAPTER 10-SHAPING UP 111Sections A
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CHAPTE R 10-SHAPING UP 113DRAW 2 AT
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CHAPTER 10-SHAPING UP 115printed at
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CHAPTER 10-SHAPING UP 117Exercises1
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120 APPLE II COMPUTER GRAPHICS1 REM
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122 APPLE II COMPUTER GRAPHICSLet's
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124 APPLE II COMPUTER GRAPHICSJ28 :
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126 APPLE II COMPUTER GRAPHICS670 X
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128 APPLE II COMPUTER GRAPHICS71¥l
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130 APPLE II COMPUTER GRAPHICS100 R
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132 APPLE II COMPUTER GRAPHICSAs we
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12Byte-Move ShapesObjectivesAfter r
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CHAPTER 12-BYTE-MOVE SHAPES 13729JJ
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CHAPTER 12-BYTE-MOVE SHAPES 139l!il
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CHAPTER 12-BYTE-MOVE SHAPES 141POKE
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CHAPTER 12-BYTE-MOVE SHAPES 1431BYT
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CHAPTER 12-BYTE-MOVE SHAPES 145Agai
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148 APPLE II COMPUTER GRAPHICSprovi
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150 APPLE II COMPUTER GRAPHICSaroun
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152 APPLE II COMPUTER GRAPHICS3 : 2
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154 APPLE II COMPUTER GRAPHICSdesir
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156 APPLE II COMPUTER GRAPHICSso ma
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158 APPLE II COM PUTER GRAPHICSfigu
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160 APPLE II COMPUTER GRAPHICSHPLOT
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162 APPLE II COMPUTER GRAPHICSset u
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164 APPLE II COMPUTER GRAPHICStoget
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166 APPLE II COMPUTER GRAPHICSThen
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168 APPLE II COMPUTER GRAPHICSyou s
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170 APPLE II COMPUTER GRAPHICS-$960
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172 APPLE II COMPUTER GRAPHICSand i
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174 APPLE II COMPUTER GRAPHICSsome
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176 APPLE II COMPUTER GRAPHICSTable
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ZS$==e
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GlossaryA particular number that co
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GLOSSARY 183HI-RES. High Resolution
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GLOSSARY 185SEPARATION. Any one of
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Editoi:(s)Hi-Res, 66, 100Low- Res,
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