Taken from here:
http://groups.google.com/group/comp.lang.lisp/browse_thread/thread/b1f63504e8f3c484/c1c1e0935951b304#c1c1e0935951b304
Sample code from common lisp:
(defun calcular-color (valor)
(round (* (expt 2 24) valor)))
(defun saltarín (&key (máximo 100000) (a -1000) (b 0.1) (c -10)
(x0 -1500.0) (y0 -1500.0) (x1 500.0) (y1 500.0))
(clc:show-canvas 500 500)
(let ((ancho (/ clc:*width* (- x1 x0)))
(alto (/ clc:*height* (- y1 y0))))
(do ((x 0 (- y (* (signum x) (sqrt (abs (- (* b x)
c))))))
(y 0 (- a x))
(iteraciones 0 (1+ iteraciones)))
((= iteraciones máximo))
(clc:set-pixel (round (+ (* ancho (- x x0))))
(round (+ (* alto (- y y0))))
(calcular-color (/ iteraciones máximo))))
(clc:repaint)))
My newLISP translation:
(define (round roundnum roundret)
(if (float? roundnum)
(if (<=(sub roundnum (floor roundnum)) 0.5)
(setq roundret (integer(floor roundnum)))
(setq roundret (integer(ceil roundnum)))
)
)
(if (integer? roundnum)
(setq roundret roundnum)
)
roundret
)
(define (calcularcolor valor)
(round (* (pow 2 24) valor))
)
(define (signum svalue sret)
(cond
((= svalue 0.0)
(setq sret 0)
)
((< svalue 0.0)
(setq sret -1)
)
((> svalue 0.0)
(setq sret 1)
)
)
)
(define (saltarin a b c x0 y0 x1 y1 maximo)
(let ((ancho (div 500 (sub x1 x0)))
(alto (div 400 (sub y1 y0)))
(x 0)
(y 0)
(iteraciones 0)
)
(do-until (= iteraciones maximo)
(begin
(setq x (sub y (mul (signum x) (sqrt(abs(sub (mul b x)c))))))
(setq y (sub a x))
(setq iteraciones (+ iteraciones 1))
;; This section should draw on a 500*400 neobook image
; (hpwImagePixels "RImage1"
; (round (add (mul ancho (sub x x0))))
; (round (add (mul alto (sub y y0))))
; (calcularcolor (/ iteraciones maximo))
; )
)
)
)
)
Any comments if translation is correct?
in 'roundnum' and in 'signum' you don't need those 'ret'- variables. Instead much shorter:
(define (signum svalue)
(if (< svalue 0) -1
(> svalue 0) 1
0)
)
'roundnum'c an also made be shorter in several ways:
(define (roundnum num)
(if (> num 0)
(int (add num 0.5))
(int (sub num 0.5)))
)
Lutz
Thanks for the code. As always much shorter and more lispy.
But I was not sure if I translate the 'let' and 'do' structure right from common lisp. And since I have not understand the original code completly I am not sure that I get the right coordinates for the drawing code. Have to further test.