RANDOM USER PROJECTS
Psychedelic Flythrough of the Mind of a Computer
Epoch: a space combat game
"Midnight Crash," from ETC's Building Virtual Worlds class.

Panda3D Manual: Flock

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.


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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>
<syntaxhighlight lang="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.
 
</syntaxhighlight>
 
 
-----
 
 
<b>The full working code in Panda3D :</b>
 
<syntaxhighlight lang="python">
import direct.directbase.DirectStart
from panda3d.core import *
from direct.showbase.DirectObject import DirectObject
from direct.task import Task
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()
</syntaxhighlight>
 
<b>To get the full working demo, please visit : </b>
 
https://sites.google.com/site/etcpandai/documentation/steering-behaviors/flock/PandAIFlockExample.zip?attredirects=0&d=1