I've written a LISP function that uses recursion to draw a picture.
The proceedure is:
f(x,y,r):
1: choose a random theta
2: call f(x+r*cos(theta), y+r*sin(theta), r/2)
3: repeat step 2 for another random theta
4: Draw a circle centre (x,y), radius r.
ie, each circle drawn has 2 smaller circles centred on it's circumference,
with half the first circle's radius. The proceedure terminates when the
circles are smaller than a pixel.
I've added color to the picture, so that each level has a different
color. The problem is, I'm plotting all the circles on one branch, and then
all the circles on another branch, which doesn't look great because the
branches sometimes overlap. What I want to do is draw all the circles on
the last level (ie. the smallest ones), then on the next level, etc. until
the biggest circle is drawn.
My problem is that although I've been using recursion for a couple of
years now, I can't figure out how to do this. I'm sure I should be able to
do it just by changing the order of the steps outlined above.
Any suggestions...?
Thanks in advance, bill
In article <········································@unicorn> bill <·······@unicorn.ccc.nottingham.ac.uk> writes:
I've written a LISP function that uses recursion to draw a picture.
The proceedure is:
f(x,y,r):
1: choose a random theta
2: call f(x+r*cos(theta), y+r*sin(theta), r/2)
3: repeat step 2 for another random theta
4: Draw a circle centre (x,y), radius r.
ie, each circle drawn has 2 smaller circles centred on it's circumference,
with half the first circle's radius. The proceedure terminates when the
circles are smaller than a pixel.
I've added color to the picture, so that each level has a different
color. The problem is, I'm plotting all the circles on one branch, and then
all the circles on another branch, which doesn't look great because the
branches sometimes overlap. What I want to do is draw all the circles on
the last level (ie. the smallest ones), then on the next level, etc. until
the biggest circle is drawn.
My problem is that although I've been using recursion for a couple of
years now, I can't figure out how to do this. I'm sure I should be able to
do it just by changing the order of the steps outlined above.
Any suggestions...?
Thanks in advance, bill
Try something like this:
(defun f (x1 y1 x2 y2 r)
(when (> r 1)
(let ((theta1 (* (random 1.0) (* 2 pi)))
(theta2 (* (random 1.0) (* 2 pi))))
(f (+ x1 (* r (cos theta1))) (+ y1 (* r (sin theta1)))
(+ x2 (* r (cos theta2))) (+ y2 (* r (sin theta2)))
(truncate r 2)))
(draw-circle x1 y1 r)
(draw-circle x2 y2 r)))
--
Ken Anderson
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