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

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92 APPLE II COMPUTER GRAPHICSHEX HEX BIT DOT....h.PP3§§ ___ Y8------8IIfiN ______ EIIBN __2!il!il!il !ill !il!il!il!il !il!il!ill24!il!il 81 l!il!il!il !il!il!ill28!il!il !il2 !il!il!il!il !il!ill!il2C!il!il 82 l!il!il!il !il!ill!ilJ!il!il!il !il4 !il!il!il!il !ill!il!ilJ4!il!il 84 l!il!il!il !ill!il!ilJ 8!il!il !il8 !il!il!il!il l!il!il!ilJ C!il!il 88 l!il!il!il l!il!il!il2!iJ8!il l!il !il!il!ill !il!il!il!il248!il 9!il l!il!ill !il!il!il!il288!iJ 2!il !il!ill!il !il!il!il!il2C8!il A!il . l!ill!il !il!il!il!ilJ !il8!il 4!il !ill!il!il !il!il!il!ilJ48!il C!iJ ll!il!il !il!il!il!ilFigure 9-3.X------X-------X------X-------X------X-------X------X-------X------X-------X------X-------X------XPlace the values in memory by typing2!il!iJ!iJ : !ill24!iJ!il : 8128!iJ!iJ : !il2J48!iJ : C!ilLooking at the dot patterns, the expected result is seven pairs of dots, withone dot of the pair directly above the other.However, when you enter the values, what you get is a diagonal line;the pairs of dots are not stacked as we expected, even though the samedot was turned on in each byte of the pair. This phenomenon relies on thefact that the fi rst byte in each pair was in color group one, and the secondbyte was from group two, as determi ned by the color bit on the left side ofthe byte.One byte of screen memory actually controls fou rteen dots on thescreen, and the two sets of seven dots are interleaved as shown in Figure9-4.DOT # 1 2 3 4 5 6 7l•l•l•l•l•l•l•l•l •l•l•l•l•l • I• GROUP 1i GROUP 2Figure 9-4. Double dot picture.
CHAPTER 9-Hl-RES COLOR 93One set of seven dots may be displayed by setting the color bit to displaygroup 1, and the other seven are displayed by setting the color bit to group2. For example, change the group two value in location $24(/)(/), which ispresently 1(/)(/)(/) (/)(/)(/)1, to the equ ivalent group one value, (/)(/)(/)(/) (/)(/)(/)1, andthen back again by typing:2400 : 012400 : 81You will see the dot in line two move slightly to the left, and then back tothe right even though in both cases it was the left-most dot of the groupbeing displayed.The point is that there are actually 56(/) dots across the Hi-Res screen,though only half the dots in any byte are available at any one time. Thefact that the group 2 dots are slightly to the right of the group 1 dots maybe exploited to draw a smoother line than possible with just one colorgroup, as we did in the example, or to smooth the outli nes of figures onthe screen in order to improve their looks.How1s That Again ?The result of all this discussion is that there are 56(/) dots across the Hi-Resscreen, 28(/) of which are potentially displayable. There are 14(/) pairs ofdots available when generating color, and all the data for a line on thescreen must fit into 4(/) bytes. You use the units and model which are mostconvenient for your immed iate purpose.Hither, Dither, and YonAccord ing to the Apple documentation, there are only six colors availablein Hi-Res mode, including black and white. Since Apple built the computerone would expect them to be correct, and they are-sort of. Thereare programs available in Hi-Res which use many more than six colors,and that seems to contradict the reference manuals.As you have seen for yourself, the dots on the Hi-Res screen are trulycapable of producing only black, white, violet, blue, green, and orange;but when you add to that a good measure of programmer imagination andcreativity, it is possible to artificially produce extra hues by a process called"dithering."Run the following program.10 REM DITHER DEMO20 REM30 DLAY = 200 : REM DELAY VALUE40 SZ = 50: REM SIZE
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APPLE IICOMPUTERGRAPHICSKen William
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Contents1 Introduction 12 Computer
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1IntroductionThe level of graphics
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4 APPLE II COMPUTER GRAPHICSmachine
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6 APPLE II COMPUTER GRAPHICScompute
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8 APPLE II COMPUTER GRAPHICSzeros i
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10 APPLE II COMPUTER GRAPHICSthe sy
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•
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14 APPLE II COMPUTER GRAPHICSdiffer
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16 APPLE II COMPUTER GRAPHICSDOS ve
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18 APPLE II COMPUTER GRAPHICSThe po
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4APP LESO FTExtensionsObjectivesAft
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CHAPTER 4-APPLESOFT EXTENSIONS 23va
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CHAPTER 4-APPLESOFT EXTENSIONS 251
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Introducing -Diskette to Accompany
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5Graphics Modes andSoft SwitchesObj
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CHAPTER 5-CRAPHIC MODES AND SOFT SW
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CHAPTER 5-GRAPHIC MODES AND SOFT SW
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CHAPTER 5-CRAPHIC MODES AND SOFT SW
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40 APPLE II COMPUTER GRAPHICSthe le
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Page 56 and 57: 48 APPLE II COMPUTER GRAPHICS3 PLOT
Page 58 and 59: 50 APPLE II COMPUTER GRAPHICSType t
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Page 62 and 63: 54 APPLE II COMPUTER GRAPHICScolor.
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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
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Page 94 and 95: 86 APPLE II COMPUTER GRAPHICSDOTBIT
Page 96 and 97: 88 APPLE II COMPUTER GRAPHICSIn Fig
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Page 104 and 105: 96 APPLE II COMPUTER GRAPHICSone of
Page 107 and 108: 991 111ObjectivesAfter reading Chap
Page 109 and 110: CHAPTER 10-SHAPING UP 101A closed d
Page 111 and 112: CHAPTER 10-SHAPING UP 103In the fir
Page 113 and 114: CHAPTER 10-SHAPING UP 105( (J(J) ha
Page 115 and 116: CHAPTER 10-SHAPING UP 107as the com
Page 117 and 118: 6 POKE 232,: POKE 233 ,37 REM8 REM
Page 119 and 120: CHAPTER 10-SHAPING UP 111Sections A
Page 121 and 122: CHAPTE R 10-SHAPING UP 113DRAW 2 AT
Page 123 and 124: CHAPTER 10-SHAPING UP 115printed at
Page 125: CHAPTER 10-SHAPING UP 117Exercises1
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Page 134 and 135: 126 APPLE II COMPUTER GRAPHICS670 X
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Page 143 and 144: 12Byte-Move ShapesObjectivesAfter r
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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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154 APPLE II COMPUTER GRAPHICSdesir
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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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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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