Happy Fourth of July!
07-03-2021, 05:22 PM
Post: #1
 robve Member Posts: 215 Joined: Sep 2020
Happy Fourth of July!
To celebrate the 4th, I've written a short program to plot a "fireworks star" of four dragons (dragon curves) on one of my calculators, an early 80s "Portable Computer":  The annotated fourdragons.bas BASIC program:

Code:
' DRAGON CURVE 4x NESTED DRAWN COUNTER CLOCKWISE
' For SHARP PC-2500

' S-BASIC has no subroutine arguments, so let's use a stack instead
' S-BASIC supports GOSUB recursions up to 10 levels deep, we use computed
' GOTOs instead with return line number R saved on the stack

' A recursive turtle graphics DragonCurve algorithm:
'
'   proc DragonCurve(sign, depth)
'      if depth == 0 then
'         forward(4)
'      else
'         DragonCurve(1, depth-1)
'         left(sign * 90)
'         DragonCurve(-1, depth-1)
'      endif
'   endproc
'   right(depth * 45)
'   DragonCurve(1, 10)

' VARIABLES
'  D       depth parameter (between 2 and 12, recommend 10)
'  N       line length (recommend 4 for D up to 12)
'  X,Y     pen cursor position
'  A       angle of pen direction
'  C       color rotation
'  S       sign parameter
'  R       return line number, to return to the next line
'  P       stack pointer
'  A()     auto-array stack starting at 27 (after Z)
'  E,F,G,H 4*sin(0,90,180,270) = A(5+A)
'  I,J,K,L 4*cos(0,90,180,270) = A(9+A)

10 CLEAR: D=10, N=4, E=0, F=N, G=0, H=-N, I=N, J=0, K=-N, L=0, P=27
20 CONSOLE 160: LPRINT CHR$27;"b": LPRINT "M240,-240": LPRINT "I" 30 FOR C=0 TO 3 40 LPRINT CHR$ 27;STR$C: LPRINT "H": X=0, Y=0, A=D/2+C AND 3 50 R=60, S=1: GOTO "DC" 60 NEXT C 70 LPRINT "M0,-240": LPRINT CHR$ 27;"0": LPRINT CHR\$ 27;"a": CONSOLE 39: END

' DragonCurve(S,D) entry
100 "DC" IF D>1 GOTO 130
110 X=X+A(9+A),Y=Y+A(5+A): LPRINT "D";X;",";Y: A=A-S AND 3
120 X=X+A(9+A),Y=Y+A(5+A): LPRINT "D";X;",";Y: GOTO R
' push argument S, return R
130 A(P)=S, A(P+1)=R, P=P+2, D=D-1
140 R=150, S=1: GOTO "DC"
150 A=A-A(P-2) AND 3
160 R=170, S=-1: GOTO "DC"
' DragonCurve exit: pop S, restore D and return
170 P=P-2, S=A(P), D=D+1: GOTO A(P+1)

This program draws four dragon curves from the center at different angles and colors. Each curve is of degree D=10. The degree and line length can be adjusted to create smaller or larger graphs.

- Rob

"I can count on my friends" -- HP 71B,Prime|Ti VOY200,Nspire CXII CAS|Casio fx-CG50...|Sharp PC-G850,E500,2500,1500,14xx,13xx,12xx...
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