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Animation is the process that puts life into computer games, but has far wider uses. The ability of a computer to create, move and display visual information has only reached the home market fairly recently,and is becoming a very popular and interesting application for users at all levels. Computer graphics is a term that means different things to different people, but generally covers images that are com puter generated, modified, stored and displayed but need not necessarily be animated. To a businessman, 'graphics' means histograms, graphs and other methods of presenting financial information visually; to a railway signalman the mimic display showing train moves is a form of computer graphic; to a student pilot on an aircraft simulator the realistic images are computer generated. Com puter aided design perhaps involves the most complicated im agery of all, think about car design as an example. A good deal of computer graphics is merely static images that can be displayed when required, animation is the art of making those images appear to move in such a way that the impression of a lifelike object is created. Animation is an art that predates the computer revolution by quite a long time and its application is a practised skill. Cartoons are a much loved example of film animation and such films have given pleasure to millions, but few of these millions have ever given much thought to the sheer effort involved in producing those cartoons. In one second of film there will be twenty four frames and each frame is an in dividual picture showing a stage in the motion of the animated object. It doesn't take much mental arithmetic to work out how many individual pictures there are likely to be in a ten minute cartoon feature. Cartoons are an example of drawn animation that uses the skill of an animator to draw a sequence of individual pictures which, when filmed, give the impression of motion. There are other techniques of animationmodel, cutout and rostrum (con trolled camera) animation are examples.These techniques are more suitable to the use of computers to aid such activity, drawn animation is more directly applicable to using computers to replace manual techniques and thid is the main topic of discussion here. Animators in the film industry are skilled people and the sue- 32 GRAPHICS Wise Moves Michael Spencer shows us some ways of getting things moving around the screen. cess of the work depends on their grasp of two factors-timing and realism. Correct timing can convey the impression of animation well and that timing ought to reflect the behaviour in the real world of the object being animated. Realism ensures that the object and its behaviour reflect the laws of motion and the presence of gravity. These techniques have been built up over many years and it is only their application in the use of computers that is new — the computer screen is only another medium on which to display images (it may be called electronic paper). The computer may also be a means to an end, com puters as animators' tools are having an impact on the film industry. Remember the Walt Disney film TRON about a computer programmer and his battle against a wayward super computer? A good deal of that film was made by using computer animation and still graphics a novel approach that created a stunning impact. Computers can take the tedium out of the process of producing images for animation a single image can be manipulated to a new position, size or shape by applying mathmatical routines. Taken to an extreme it may be possible to produce a complete film in a few years time, and indeed a Hollywood film company is using a CRAY super computer to cope with the fantastic number of calculations involved in such processes. This machine made its debut code cracking in American for the Government and has since made contributions in many other fields. Animation itself involves three basic processes preparation of the image, manipulation and display. It is the manipulation that is at the heart of the technique of anima tion. The computer offers the electronic paper for us to exploit and the characteristics of that paper determine what sort of animation is possible. There are three sorts of graphics that can be created on most home computers block, pixel and line graphics. Block graphics involve the use of character sized shapes (see the top row of the Spectrum keyboard} which may be used individually or as part of larger shapes which can be moved around the screen. The pro gram in figure one creates such a shape and moves it around. The program is reasonably effective and shows some of the basics of simple animation. An image drawn on the screen is erased and a new image created in a different place which gives the apperance of motion. A variation a very reasonable resolution of 176 by 256 pixels each of which can be individually set and tested. In case of a single pixel being moved around the screen the technique is similar to block graphics, the pixel is set and unset (erased) and moved to a new position after appropriate delay. Groups of pixels make up the high resolution screens that form the bulk of a computer games attractions. These shapes can be animated by dealing with the individual pixelsthat make them up. Collision deted- t0 R£M BLOCK GRAPH . C ANIMATION 2SS CLS LET 4 0 LET FOR 1-0 TO 21 60 PRINT AT I,12|A* 7 0 PAUSE 3 60 PRINT AT I,121B*
collision detection where the place the pixels will occupy next is teasted to see if it is possible to move there. A realistic rebound is programmed in rather than a straight reversal of course if a collision is detected. Lines Line graphics can be the most satisfying because they can be used to make up wire images of objects, giving a three dimen sional effect. That object can be moved realistically around the screen and even rotated around variour points. Wire images have been used in some com puter games but are probably best known in such applications as building and car design. The program in figure 3 is an example. These are the three main ways of producing graphics on most home computers and for tunately we have access to all three on the Sinclair Spectrum. It has to be said that the best animation on the Spectrum will be written using machine code rather than BASIC because machine code is a good deal faster. BASIC is easy to unders tand, and has b^en used in the examples here for clarity, though it can cause flickering and other odd eff3Cts and detra. t from the effect that you ire trying to achieve The actual process of anima non on computers is a good deal different from that using hand drawn images and film. A com puter really only undertands numbers, so that images shown have to be digitised to coordinates and these coordinates manipulated to produce new images in dillerent positions. Do that quickly enough and you have animation. In extreme cases a single drawing may be made and many different images made by mathematical manipulation. For example, an image may be made wider or taller by altering values along one axis, give a computer two images, one bigger than the other and the computer can be programmed to produce a new image between the two sizes — this is known as an in betweening. Animation implies change, so that images presented sequentially appear to move. The basis of animation involves a number of key elements that help produce the desired effect. The obvious is change in size or shape, others include change in speed, angle, colour, position and perspective - remember these are animation techniques and not computer techniques. We have all seen some really funny cartoons where some of the humour has been about the ability of a character or object to survive impossibly destructive situations for example holding a bomb when it goes off, being squashed flat or streched. Twist, skew, shear, bend and explode can all be used to great effect. Explosions seem to characterise the even popular arcade game and it is worth knowing how to do this. Bang! ZX COMPUTING DECEMBER/JANUARY 1985 The basis of an explosion effect is that the image breaks up and moves apart from a central point. The image is initially chopped or minced into short lines or pieces and these move radially ZX CRAPHICS out from a central point. Most explosions are a variation of this, for example the bus of the exploded image can be made to tumble, flicker or leave trailing images as it moves apart. The image may be exploded into single pixels that change colour rapidly as they move outwards. A computer can generate useful sound effects to accompany this visual extravaganza which makes the whole process more effective. Manipulation in size is one technique that a computer can do quickly without the need for new images to be drawn, digitis ed and stored. It is simply a mat ter of arithmetic to alter the size of an object. For example characters can be made larger by scanning the character 10 REM PIXEL GRAPHIC ANIMATION 20 REM AND COLLISION DETECTION 30 CLS 40 REM DRAW BORDER 50 FOR 1=1 TO 20: PRINT AT 1,1 I"B": PRINT AT I,301 60 NEXT I 70 FOR 1=1 TO 30: PRINT AT 1,1 PRINT AT 20,IJ B FL* 80 NEXT I 90 GO TO 220: REM MAIN PART 100 REM PLOT SUBROUTINE 110 PLOT X,Y 120 PAUSE 4 130 RETURN 140 REM UNPLOT SUBROUTINE 150 PLOT OVER 1;X,Y 160 RETURN 170 REM COLLISION DETECTION 180 REM SUBROUTINE 190 IF POINT (X+XDIR,Y+YDIR)=1 AND POINT (X+XDIR,Y+YDIR+1>-1 AN D POINT (X+XDIR,Y+YDIR-1)-1 THEN LET XDIR-XDIR*-1 200 IF POINT (X+XDIR,Y+YDIR)-1 AND POINT (X+XDIR+1,Y+YDIR>=1 AN D POINT (X+XDIR-1,Y+YDIR)-1 THEN LET YDIR"YDIR*-1 210 RETURN 220 REM MAIN LOOP 230 LET X-70: LET Y-100: LET XD IR=--3. 1 : LET YDIR-1 240 GO SUB 170: REM COLLIDED? 250 GO SUB 110: REM PLOT 260 GO SUB 140: REM UNPLOT 270 LET X=X+XDIR 280 LET Y=Y+YDIR 290 GO TO 240 Figure 2 square and reproducing the image larger or smaller. The pro grarne is figured four does this four one character and displays an image twice the size at a different place on the screen. It achieves this by scanning all the sixty four pixels in the character square and displaying them doubled up on both axis. It is a simple matter to adapt this program to reproduce a character that is stretched taller or wider by only adjusting the values on one or the other axis. This technique, because it works at the pixel level will also expand any shape. In BASIC it is rather slow, in machine code it is much faster and can be used to great effect. Perhaps the most exciting possibility for a home computer user is to make use of line graphics and produce a three dimensional representation of an object that can be rotated in any given direction and create some illusion of movement. The wire frame image depends on coordinate geometry to manipulate it, it is a matter of numbers and few rules. The big gest problem is that the television or other computer screen is only two-dimensional. Perhaps one day hologram technology will have advanced enough so that three-dimensional images can be projected into a living room like a super television, but until then we must rely on the eye being fooled by twodimensional trickery. Perspective drawings do this and the Renaissance artists were masters of the art and produced some remarkable paintings and drawings. The keys to such works of art is the 'vanishing point". Looking along railway lines, the tracks appear to converge at a point — this is a vanishing point. These drawings are made with reference to such a point which is often off the paper. 3D In three-dimensional reality we can describe an object by reference to three axis- x,y andz as they are conventionally known. When measuring an object we normally described the dimensions in terms of length, width and height, but in order to describe an object in terms suitable for computer graphics we must describe the object in distances from an origin point. The origin can be a corner of the object itself or further away, the object may be viewed from the origin or another point. This introduces the idea of how we can • I L
Page 1: The Magazine For All Sinclair users
Page 4 and 5: welcome Ray says hello. Editor: Ray
Page 6 and 7: At last as we all knew would happen
Page 8 and 9: short visit my Spectrum was working
Page 10 and 11: A letter from Eclipse Software SHOP
Page 12 and 13: Framed The Gordon Microframe is one
Page 14 and 15: HARDWARE Getting into Print through
Page 16 and 17: IHARDWARE REVIEW QL Delta Disk Ray
Page 18 and 19: HARDWARE The Spectrum Beta Plus Dis
Page 20 and 21: USA NEWS Across the Pond by Mark L.
Page 22 and 23: QL HARDWARE Micro Peripherals QL Di
Page 24 and 25: (SPECTRUM GRAPHICS! Screen Master F
Page 26 and 27: top of the display in such a way th
Page 28 and 29: ZE USR ST: RETURN 1670 RANDOMIZE US
Page 30 and 31: 3^30 LET G*=INKEY
Page 34 and 35: 10 REM CUBOID DRAWING 20 LET OX-=30
Page 36 and 37: (SPECTRUM GRAPHICS! Spirogram Movin
Page 38 and 39: FF6B 31 FF6C B9 FP6D 01 FF6E EB FF6
Page 40 and 41: As we see this old year out and wel
Page 42 and 43: zapping Your Graphics zx looks at s
Page 44 and 45: Light Screen Part Nine: by Toni Bak
Page 46 and 47: Overall then, it would seem that th
Page 48 and 49: JA01EJ je FE|0 JOBJ )»1EJ 18AP FSO
Page 50 and 51: ^ m HARDWARE — The Perfect Keyboa
Page 52 and 53: the wrong size and pressure. It loo
Page 54 and 55: BINARY AND HEX Binary and Hex The A
Page 56 and 57: Yes, of course, and in exactly the
Page 58 and 59: SOUNDS speakeasy Kai Webber has com
Page 60 and 61: IU 9 RECORD MODE 20 ORG 32768 SOUND
Page 62 and 63: JURY we, the jury Daley Thompson's
Page 64 and 65: The Rats Hodderand Stoughton £7.95
Page 66 and 67: SOUNDS The Sound Of Music John Ains
Page 68 and 69: +5V Figure 1 Diagram of 'he 8912 PS
Page 70 and 71: SOUNDS HEX DISASSEMBLY OF *C0MMRH0S
Page 72 and 73: F8E4 030F 1710 OUT .« FAE6 23 FRE7
Page 74 and 75: Harwood's Hypothesis This month we
Page 76 and 77: ZX81SCENE ZX81 Chatterbox Julian Ch
Page 78 and 79: OL into The Archive The QL's flexib
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Page 82 and 83:
EDUCATIONAL REVIEWS Mike Edmunds gr
Page 84 and 85:
Anthony Marlow from Cheshire has se
Page 86 and 87:
0« , o < SANTA'S CAME Derek Mearns
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199 RETURN "PI0 REM SCREEN 1 902 BR
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The lure of thai yellow stuff, I ca
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96 1730 IF CDODR THEN GO TO 4000 19
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SPECTRUM GAME Pim Quakkelaar gives
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ZX81 STRATEGY 321 I F Di = 3 THEN G
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Page 112 and 113:
HARDWARE REVIE Derek Mearns has bee
Page 114 and 115:
IF YOU USE YOUR COMPUTER TO PLAY GA
Page 116 and 117:
ZX81 club Dear Editor, In March of
Page 118 and 119:
Conversion (PROGRAMMING TIPS) tips
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Lineage: 40p per word E 3 Semi disp
Page 122 and 123:
SPECTRUM RGB OUTPUT MODULE THE LEAD
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SPECTRUM AMSTRAD Jl\0_l_ sales dept
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