User:Laurier Rochon/prototyping/l-systems

L-Systems

Discovery of the day : TURTLE! (not TurtleWorld, the library)

It actually appears that Python has built-in turtle graphics, meaning that we can bypass BOB (being in the 'swampy folder' etc., and just use a 'pointer' triangle, with much clearer methods. This is the page for it. It's well documented - for example, you can use 'setcoords(x,y)' to set the pointer at the right spot. The method 'getheading' is also tremendously useful in knowing what angle bob is oriented towards. One big problem with turtle vs turtle world : it's slowwwwwwwwwwwwww. Max speed is '10', which equates to about '1' in Turtle World terms.

Going green with recursive algorithms

Takes about 20-30 minutes to generate at MAX speed (with TurtleWorld library. About 10X with native turtle lib)

Rules:

• X -> F-[[X]+X]+F[+FX]-X
• F -> FF

Interpretation:

• Start symbol = X
• F = forward 2
• + = right 25
• - = left 25

Rule:

• F -> FF-[-F+F+F]+[+F-F-F]

Interpretation:

• Start symbol = F
• F = forward 5
• + = right 25
• - = left 25

(the tree rules I got here.)

---

Using basic transformation rules such as :

• Axiom: F-F-F-F
• Rule : F -> FF-F-F-F-FF
• Angle: 90
• Steps: 4

What the symbols mean

• F is forward by X pixels
• + is turn Y degrees
• - is turn -Y degrees
• [ is record the current state
• ] restore the matching last ] state

Will yield something like :

Other set of rules...

Soft (Python)

(with TurtleWorld)

from TurtleWorld import *

world = TurtleWorld()
bob = Turtle()
#make it FAST!
bob.delay = 0.0001

#draw upwards, plz
lt(bob,90)
#gimme some room...we'll fullscreen the window
bob.x=200
bob.y=-300

#starting axiom
n = 'X'

#replacement rules
s1 = 'X'
s2 = 'F-[[X]+X]+F[+FX]-X'
s3 = 'F'
s4 = 'FF'

#number of steps
steps = 7

for i in range(steps):
	#apply the rules, do the replacements
	n = n.replace(s1,s2)
	n = n.replace(s3,s4)

#angle to turn
a = 25

#declare my arrays
xx = []
yy = []
angle = []

#go through all characters of my string
for i in n:
	#go forward
	if i == 'F':
		bob.fd(1)
	#turn left
	if i == '+':
		bob.lt(a)
	#turn right
	if i == '-':
		bob.rt(a)
	#record current state
	if i=='[':
		xx.append(bob.get_x())
		yy.append(bob.get_y())
		angle.append(bob.get_heading())
	#restore last state...
	if i==']':
		#we're gonna move around, put the pen up
		bob.pu()
		#change x and y
		bob.x = xx[len(xx)-1]
		bob.y = yy[len(yy)-1]
		#cancel whatever angle you're in
		bob.rt(bob.get_heading())
		#turn to new angle
		bob.heading = angle[len(angle)-1]
		#pop the x,y and angle off their stacks
		xx.pop()
		yy.pop()
		angle.pop()
		#ready to draw again...
		bob.pd()


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