The previous code in this and this section is rewritten to have more control of branching angles and branching probabilities. In the LineAgnet class, instance fields of angle, pct1, pct2 and pct3 are added as the variables for branching angle, the percentage of the probabilities to branch left, right and straight. Each variables are defined at setup() method through the constructor of LineAgent class.

add_library('igeo')

def setup() : 
    size(480,360,IG.GL)
    IG.duration(150)
    LineAgent(IG.v(0,0,0), IG.v(1,0,0), PI/3, 20, 30, 100).clr(0.3)
    LineAgent(IG.v(100,0,0), IG.v(-1,0,0), PI/2, 20, 0, 100).clr(0.3)
    LineAgent(IG.v(-20,50,0), IG.v(0,-1,0), PI/2, 10, 0, 100).clr(0.3)
    LineAgent(IG.v(0,-100,0), IG.v(0,1,0), PI/2, 10, 10, 100).clr(0.3)
    LineAgent(IG.v(-40,0,0), IG.v(1,0,0), PI*0.4, 20, 30, 100).clr(0.3)
    LineAgent(IG.v(-100,40,0), IG.v(1,1,0), PI/2, 10, 10, 100).clr(0.3)

class LineAgent(IAgent) : 
    length = 2
    clearance = 1.99 #less than length
    
    def __init__(self, pt, dir, ang, \
                 percent1, percent2, percent3 ) : 
        self.pt1 = pt
        self.pt2 = pt.dup().add(dir.dup().len(LineAgent.length))
        self.isColliding = False
        self.angle = ang
        self.pct1 = percent1
        self.pct2 = percent2
        self.pct3 = percent3
    
    def interact(self, agents) : 
        if self.time() == 0 : #only in the first time
            for agent in agents : 
                if self.isColliding : 
                    return
                if isinstance(agent, LineAgent) : 
                    if agent is not self : #agents include "self"
                        # checking clearance of end point
                        if agent.pt2.dist(self.pt2) < LineAgent.clearance : 
                            self.isColliding = True

    def update(self ) : 
        if self.isColliding : 
            self.del()
        elif self.time() == 0 : #if not colliding
            ICurve(self.pt1,self.pt2).clr(self.clr())
            dir = self.pt2.dif(self.pt1)
            
            r = self.red()+IRand.get(-0.03,0.03)
            g = self.green()+IRand.get(-0.03,0.03)
            b = self.blue()+IRand.get(-0.03,0.03)
            
            if IRand.pct(self.pct1) : #bend
                LineAgent(self.pt2,dir.cp().rot(self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct2) : #bend the other way
                LineAgent(self.pt2,dir.cp().rot(-self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct3) : #straight
                LineAgent(self.pt2,dir.cp(),\
                         self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)

Next, blocking agents are added to exclude some lines on some location. The class of blocking agents is BlockAgent. Comparing with the previous example of blocking agents, there is a difference in the location of the code which checks the location of agents and deletes. In the previous example, location checking is done in the interact method of LineBlockAgent but in the code below, LineAgent itself check the location of blocking agent inside its interact method. In the code below, branching angle and probability are randomly defined at setup method.

add_library('igeo')

def setup() : 
    size(480,360,IG.GL)
    IG.duration(150)
    for i in range(15) : 
        LineAgent(IRand.pt(300,200,0), IRand.dir(IG.zaxis),\
                  IRand.get(PI*0.11,PI*0.3),IRand.get(90,100),\
                  IRand.get(50,90),IRand.get(0,20)).clr(0)
    
    BlockAgent(IG.v(0,0,0), 20)
    BlockAgent(IG.v(-30,80,0), 30)
    BlockAgent(IG.v(50,50,0), 30)
    BlockAgent(IG.v(180,150,0), 50)
    BlockAgent(IG.v(0,-120,0), 80)

class BlockAgent(IAgent) : 
    def __init__(self, p, r) : 
        self.pt = p
        self.radius = r
    
    def isColliding(self, agent) : 
        if agent.pt2.dist(self.pt) < self.radius : 
            return True 
        return False

class LineAgent(IAgent) : 
    length = 2
    clearance = 1.99 #less than length
    
    def __init__(self, pt, dir, ang, \
                 percent1,percent2,percent3) : 
        self.pt1 = pt
        self.pt2 = pt.dup().add(dir.dup().len(LineAgent.length))
        self.isColliding=False
        self.angle = ang
        self.pct1 = percent1
        self.pct2 = percent2
        self.pct3 = percent3
    
    def interact(self, agents) : 
        if self.time() == 0 : #only in the first time
            for agent in agents : 
                if self.isColliding :
                    return
                if isinstance(agent, LineAgent) : 
                    if agent is not self : #agents include "self"
                        # checking clearance of end point
                            if agent.pt2.dist(self.pt2) < LineAgent.clearance : 
                                self.isColliding=True
                elif isinstance(agent, BlockAgent) : 
                    if agent.isColliding(self) : 
                        self.isColliding=True
    
    def update(self) : 
        if self.isColliding : 
            self.del()
        elif self.time() == 0 : #if not colliding
            ICurve(self.pt1,self.pt2).clr(self.clr())
            dir = self.pt2.dif(self.pt1)
            
            r = self.red()+IRand.get(-0.02,.035)
            g = self.green()+IRand.get(-0.02,.035)
            b = self.blue()+IRand.get(-0.02,.035)
            
            if IRand.pct(self.pct1) :  #bend
                LineAgent(self.pt2,dir.cp().rot(self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct2) : #bend the other way
                LineAgent(self.pt2,dir.cp().rot(-self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct3) : #straight
                LineAgent(self.pt2,dir.cp(),self.angle,\
                          self.pct1,self.pct2,self.pct3).clr(r,g,b)

The example below changes the branching angle inside the agent itself in the middle of the propagation process. In the update method, sometimes with a certain probability, the variable angle is increased or decreased stochastically. There is another stochastic feature added for the blocking agent. The line agent sometimes ignores the blocking agent and keep propagating inside the blocking area by if-condition in the interact method of LineAgent

add_library('igeo')

def setup() : 
    size(480,360,IG.GL)
    IG.duration(150)
    LineAgent(IG.v(100,-50,0), IG.v(0,1,0), PI/2, 20,10,99).clr(0)
    LineAgent(IG.v(-50,150,0), IG.v(1,1,0), PI/2, 20,10,99).clr(0)
    
    BlockAgent(IG.v(0,0,0), 20)
    BlockAgent(IG.v(-30,80,0), 30)
    BlockAgent(IG.v(50,50,0), 30)
    BlockAgent(IG.v(180,150,0), 50)
    BlockAgent(IG.v(0,-120,0), 80)

class BlockAgent(IAgent) : 
    def __init__(self, p, r) : 
        self.pt = p
        self.radius = r
    
    def isColliding(self, agent) : 
        if agent.pt2.dist(self.pt) < self.radius : 
            return True 
        return False

class LineAgent(IAgent) : 
    length = 2
    clearance = 1.99 #less than length
    
    def __init__(self, pt, dir, ang, \
                 percent1,percent2,percent3) : 
        self.pt1 = pt
        self.pt2 = pt.dup().add(dir.dup().len(LineAgent.length))
        self.isColliding=False
        self.angle = ang
        self.pct1 = percent1
        self.pct2 = percent2
        self.pct3 = percent3
    
    def interact(self, agents) : 
        if self.time() == 0 : #only in the first time
            for agent in agents :
                if self.isColliding : 
                    return
                if isinstance(agent, LineAgent) : 
                    if agent is not self : #agents include "this"
                        # checking clearance of end point
                        if agent.pt2.dist(self.pt2) < LineAgent.clearance : 
                            self.isColliding=True
                elif isinstance(agent, BlockAgent) : 
                    if agent.isColliding(self) :  
                        if IRand.pct(80) : #ignores block agent in 20%
                            self.isColliding=True 

    def update(self) : 
        if self.isColliding :
            self.del()
        elif self.time() == 0 : #if not colliding
            ICurve(self.pt1,self.pt2).clr(self.clr())
            dir = self.pt2.dif(self.pt1)
      
            if IRand.pct(2) : #change angle occasionally
                if IRand.pct(50) : 
                    self.angle+=PI/12
                else :
                    self.angle -= PI/12
            
            r = self.red()+IRand.get(-0.03,0.03)
            g = self.green()+IRand.get(-0.03,0.03)
            b = self.blue()+IRand.get(-0.03,0.03)
            
            if IRand.pct(self.pct1) :  #bend
                LineAgent(self.pt2,dir.cp().rot(self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct2) :  #bend the other way
                LineAgent(self.pt2,dir.cp().rot(-self.angle),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)
            if IRand.pct(self.pct3) :  #straight
                LineAgent(self.pt2,dir.cp(),\
                          self.angle,self.pct1,self.pct2,self.pct3).clr(r,g,b)