A downloadable tool

PUR80 – Epicycle_bas demo by Stephen Poole, (QL Forum).

[Moved to category SCHAU, because it isn't a game; the organizer]

Code written and tested on QL and QPC2 (QL emulator).

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The original QL possessed two microdrive tape readers. These are now hard to find. Floppy disc readers could be installed, but are now rare. MSDOS and QDOS discs are formatted differently, but both types can be accessed by the ‘QPC2’ QL emulator. With this readme file, comes a program file which QPC2 will run.

But the simplest way to access the files is to UNZIP and copy them to a USB key, (which will be referred to by QPC2 as dos2_ , dos3_ or dos4_ etc).

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On PCs : Download QPC2 from its website onto your PC. Unzip, then click on the QPC2 appfile. Set ‘resolution’ to 512x256 and hit ok.

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Watch until the animation halts.

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1 WINDOW 512,256,0,0:SCALE 180,-180,-90:PAPER 0:MODE 8:CLS:AT 1,1:CSIZE 3,1
 2 PRINT'EPicycles':PAUSE 250:CLS:DIM q$(1):p=2*PI:h=30:i=RAD(3):FOR t=1 TO 6
 3 IF t<4:i=RAD(6):END IF :AT 0,1:PRINT'Rank '!t,:q=p/t:k=t:FOR c=q/2,q/4,i
 4 INK k:AT 1,1:PRINT c,:b=32766:u=640:a$='Angle':v=.76:FOR r=-h TO h STEP 20
 5 AT 2,1:PRINT a$!r!!:o=r+30:l=o+48:FOR j=-1,1:a=r*j:e=a+h:k=k+1:k=k MOD 7:zz
 6 END FOR r:k=1:END FOR c::PAUSE h:CLS:END FOR t:WINDOW#2,480,206,0,0:PAUSE u
 7 DEFine PROCedure zz
 8 IF k=0:k=1:END IF :INK k,t,0:PAUSE h:BEEP b,o,l,u,j,3:FOR f=0 TO p+c STEP c
 9 d=f*j:g=f*t+d:s=SIN(g):z=e*COS(d):x=z+r*COS(g):w=e*SIN(d):PAUSE 1:y=w+r*s
 10 IF f:LINE m*v,n TO x*v,y:END IF :m=x:n=y:NEXT f:BEEP b,o,l,u,j,3:END DEFine

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Program description :

1 Full screen : Vertical scale : black paper : 8 colours : blackout :

at top left : big characters

2 print title : pause 5 secs : blackout : Dimension Q$ ? : p circumference :

h 30°: i 3° in radians : for i(rank) = 1 to 6

3 if rank<4 i=6° in radians : end if : on 2nd row print rank : q no. of cycles :

k colour : for c sectors 1/2,1/4,i°

4 ink colour : b beep duration : u beep xstep : a$ message : v aspect ratio :

for r orientation & height = -30 to 30 step 20

5 print angle of r : o pitch1 : l pitch 2 : for j =-1,+1 width or height halves

a get the orientation : e add 30° : k change colour : ink as rank : zz draw

6 end for orientation & height : colour red :

end for sectors : pause 1/2sec : blackout :

end for rank : set listing screen : pause 13 secs

7 DEFine draw routine

8 if k=0 black ink : k irridessence : pause 1/2sec : beep warble merrily :

for f sectors around circumference

9 d ajacent side : g opposite side rank§or : s SIN(opposite) :

z COS(adjacent)*added_angle : x z+(orientation & height)*COS(g)

w COS(g)*SIN(ajacent)*added_angle : pause 1 sec : y=w+rank*s

10 if any sector : draw line arc sector : m & n are end coordinates :

end for f sectors : Beep warbling merrily : End of routine definition

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This program was rapidly written at short notice, using a few of the QL’s built in features. It is based on a much longer highly commented program I wrote.

(It took weeks to construct from simple mathematical principals).

The description is very difficult to follow, as the code is highly imbricated...

The SCALE command sets the 0,0 coordinates near the screen center. So by using negative, 0 or positive x,y values, we can use whole-circle polar coordinates.

The several FOR loops use these (– 0 +) ranges in combination, to access all quarters of the screen.

Epicycles have straight lines when the arc-sectors have the same value as the segment values. Please realise that the rotating or contra-rotating ‘discs’ have a slipping peripheral point, (which is represented by the orbital trace). This is why we can get so many different orbital designs from so little code.

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Any time the program halts, just type in RUN and hit ENTER.

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