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.. _pursue:

Pursue
======

'Pursue' is a behavior where an AICharacter moves in the direction of a target
NodePath until it reaches that entity, performing a change in direction of
motion according to the entity's motion.

{{#ev:youtube\|QdcbN3FLYVs}}

--------------

In PandAI, 'Pursue' is defined as :


.. code-block:: python
    
    aiBehaviors.pursue(NodePath target, float priority)

priority is by default
set to 1.0 and is used when using two or more steering behaviors on an
AICharacter.

--------------

The velocity at which the AICharacter pursues is determined when you first
create your AICharacter object using the AICharacter constructor.

-  Note : Pursue's direction is recalculated every frame to handle any change
   in the target's position.

The actual code working in Panda3D :


.. code-block:: 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(0,0,55,0,-90,0)
            
            self.loadModels()
            self.setAI()
            self.setMovement()
    
        def loadModels(self):
            # Seeker
            ralphStartPos = Vec3(-10, 0, 0)
            self.pursuer = Actor("models/ralph",
                                     {"run":"models/ralph-run"})
            self.pursuer.reparentTo(render)
            self.pursuer.setScale(0.5)
            self.pursuer.setPos(ralphStartPos)
            # Target
            self.target = loader.loadModel("models/arrow")
            self.target.setColor(1,0,0)
            self.target.setPos(5,0,0)
            self.target.setScale(1)
            self.target.reparentTo(render)
          
        def setAI(self):
            #Creating AI World
            self.AIworld = AIWorld(render)
     
            self.AIchar = AICharacter("pursuer",self.pursuer, 100, 0.05, 5)
            self.AIworld.addAiChar(self.AIchar)
            self.AIbehaviors = self.AIchar.getAiBehaviors()
            
            self.AIbehaviors.pursue(self.target)
            self.pursuer.loop("run")
    
            #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/pursue/PandAIPursueExample.zip?attredirects=0&d;=1