What is flocking?

Flocking is an emergent behavior and is the resultant of the following forces:

cohesion -- finds average position of neighbors and tries to move to that position separation -- object keeps a certain distance between itself and its neighbor alignment -- finds average direction in which all neighbors are moving and tries to move in that direction

Each NPC has a "visibility cone" and this is used to compute it's neighbors. The neighbors contribute towards the forces mentioned above.

Tuners:

1. The angle and length of each NPC's "visibility cone". 2. Weight of cohesion, separation, and alignment (how much each sub-behavior of flock affects the overall flocking behavior).

Note: Flocking behavior is NOT a standalone behavior. It needs to be combined with other steering behaviors such as seek, pursue, flee, evade etc. to function.

Using PandAI's flocking system:

// To create the flock
flockObject = Flock(unsigned int flock_id, double vcone_angle, double vcone_radius, unsigned int cohesion_wt, unsigned int separation_wt, unsigned int alignment_wt)

"flock_id" is a value identifying the flock.

"vcone_angle" is the visibility angle of the character (represented by a cone around it)

"vcone_radius" is the length of the visibility cone.

"cohesion_wt", "separation_wt" and "alignment_wt" is the amount of separation force that contributes to the overall flocking behavior.

Some standard values to start you off with:

Type vcone_angle vcone_radius separation_wt cohesion_wt alignment_wt

Normal Pack 270 10 2 4 1

Loose Pack 180 10 2 4 5

Tight Pack 45 5 2 4 5

You could try experimenting with your own values to customize your flock.

To add your AI Character to the above created flock

flockObject.addAiChar(aiChar)     // aiChar is an AICharacter object.

After all the AI Characters are added to the flock, add the flock to the world.

aiWorld.addFlock(flockObject)    // aiWorld is an AIWorld object.

Specify the flock behavior priority. As mentioned earlier, flock behavior works with other steering behaviors.

aiBehaviors.flock(float priority)       // aiBehaviors is an AIBehaviors object.
<code>
 
<b>Other useful flock functions:</b>
<code python>
aiWorld.flockOff(unsigned int flock_id);            // Turns the flock behavior off.
 
aiWorld.flockOn(unsigned int flock_id);           // Turns the flock behavior on.
 
aiWorld.removeFlock(unsigned int flock_id);    // Removes the flock behavior. Note: This does NOT remove the AI characters of the flock.
 
aiWorld.getFlock(unsigned int flock_id);          // Returns a handle to the flock object.

The full working code in Panda3D :

#for directx window and functions
import direct.directbase.DirectStart
#for most bus3d stuff
from pandac.PandaModules import *
#for directx object support
from direct.showbase.DirectObject import DirectObject
#for tasks
from direct.task import Task
#for Actors
from direct.actor.Actor import Actor
#for Pandai
from panda3d.ai import *
#for Onscreen GUI
from direct.gui.OnscreenText import OnscreenText
 
# Globals
speed = 0.75
 
# Function to put instructions on the screen.
font = loader.loadFont("cmss12")
def addInstructions(pos, msg):
    return OnscreenText(text=msg, style=1, fg=(1,1,1,1), font = font,
                        pos=(-1.3, pos), align=TextNode.ALeft, scale = .05)
 
class World(DirectObject):
 
    def __init__(self):
        base.disableMouse()
        base.cam.setPosHpr(0,0,85,0,-90,0)
 
        self.loadModels()
        self.setAI()
        self.setMovement()
 
    def loadModels(self):
        # Seeker
        self.flockers = []
        for i in range(10):
            ralphStartPos = Vec3(-10+i, 0, 0)
            self.flockers.append(Actor("models/ralph",
                                     {"run":"models/ralph-run"}))
            self.flockers[i].reparentTo(render)
            self.flockers[i].setScale(0.5)
            self.flockers[i].setPos(ralphStartPos)
            self.flockers[i].loop("run")
 
        # Target
        self.target = loader.loadModel("models/arrow")
        self.target.setColor(1,0,0)
        self.target.setPos(0,20,0)
        self.target.setScale(1)
        self.target.reparentTo(render)            
 
    def setAI(self):
        #Creating AI World
        self.AIworld = AIWorld(render)
 
        #Flock functions
        self.MyFlock = Flock(1, 270, 10, 2, 4, 0.2)
        self.AIworld.addFlock(self.MyFlock)
        self.AIworld.flockOn(1);
 
        self.AIchar = []
        self.AIbehaviors = []
        for i in range(10):
            self.AIchar.append(AICharacter("flockers"+str(i),self.flockers[i], 100, 0.05, 5))
            self.AIworld.addAiChar(self.AIchar[i])
            self.AIbehaviors.append(self.AIchar[i].getAiBehaviors())
            self.MyFlock.addAiChar(self.AIchar[i])
            self.AIbehaviors[i].flock(0.5)             
            self.AIbehaviors[i].pursue(self.target, 0.5)
 
        #AI World update        
        taskMgr.add(self.AIUpdate,"AIUpdate")
 
    #to update the AIWorld    
    def AIUpdate(self,task):
        self.AIworld.update()            
        return Task.cont
 
#All the movement functions for the Target
    def setMovement(self):
        self.keyMap = {"left":0, "right":0, "up":0, "down":0}
        self.accept("arrow_left", self.setKey, ["left",1])
        self.accept("arrow_right", self.setKey, ["right",1])
        self.accept("arrow_up", self.setKey, ["up",1])
        self.accept("arrow_down", self.setKey, ["down",1])
        self.accept("arrow_left-up", self.setKey, ["left",0])
        self.accept("arrow_right-up", self.setKey, ["right",0])
        self.accept("arrow_up-up", self.setKey, ["up",0])
        self.accept("arrow_down-up", self.setKey, ["down",0])
        #movement task
        taskMgr.add(self.Mover,"Mover")
 
        addInstructions(0.9, "Use the Arrow keys to move the Red Target")
 
    def setKey(self, key, value):
        self.keyMap[key] = value
 
    def Mover(self,task):
        startPos = self.target.getPos()
        if (self.keyMap["left"]!=0):
                self.target.setPos(startPos + Point3(-speed,0,0))
        if (self.keyMap["right"]!=0):
                self.target.setPos(startPos + Point3(speed,0,0))
        if (self.keyMap["up"]!=0):
                self.target.setPos(startPos + Point3(0,speed,0))
        if (self.keyMap["down"]!=0):
                self.target.setPos(startPos + Point3(0,-speed,0))
 
        return Task.cont    
 
w = World()
run()

To get the full working demo, please visit :

https://sites.google.com/site/etcpandai/documentation/steering-behaviors/flock/PandAIFlockExample.zip?attredirects=0&d=1