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Lab 5 - Actors and State Machines

Before You Start

Interacting with a moving actor

In this exercise, you have to create a character that paces around while he is unaware of you. But as soon as you come within a certain range, he stops and looks at you. While the character is watching you, you can click on him to start a conversation with him. If you have entered a conversation, you can click on something else to stop talking. If at any point you leave the character, he goes back to his pacing around. These states and the events that trigger transitions are shown in this figure.

You will need the following modules imported into your program:

import direct.directbase.DirectStart
from direct.showbase.DirectObject import DirectObject
from pandac.PandaModules import *
from direct.actor.Actor import Actor
from direct.fsm import FSM
from direct.interval.IntervalGlobal import *
from direct.task.Task import Task
from direct.gui.OnscreenText import OnscreenText
from picker import Picker
  1. Setting Up:
    Create a World class derived from DirectObject like before and set up a camera at (0,-70,2) with FOV of 50 and a near clipping plane of 0.01. Load and display the environment model called Models/environment and scale it down to 30%. Add your camera movement code from Lab 2. Verify that you can now move around the landscape.
  2. Adding a Moving Character:
    Create a Character class derived from FSM.FSM (Finite State Machine). In the constructor, you first need to call the constructor of the parent like this:
    FSM.FSM.__init__(self,"Character")

    Then you should load an Actor from the model “Models/eve” with the animation 'Walk':'Models/eve_walk'“. Place the actor at (0,-20,0) and scale it down to 80%. Start your actor's Walk animation by calling loop(“Walk”) on your instance of it. Now create a new Sequence of Lerp Intervals that first changes your actor's heading to -90 (in about 0.8 seconds) and then moves him to position (-10,-20,0) in about 9 seconds. Rotate back and move back to the original position. Now loop this interval and watch your actor pace around!

  3. Starting a State Machine:
    Create a state for pacing such that when he enters the state he paces around, but stops when he leaves the state. You do that by adding the methods enterPacing(self) and exitPacing(self). In the former, you loop the Walk animation like before, but instead of calling loop on your movement interval, call resume. This is so that he can continue moving from where he left off when he was interrupted. In the latter, you'll have to stop the walking animation, but instead of calling stop, which leaves him frozen at the first frame of the animation, you should call pose('Walk',X) where X is a number of a frame you choose so that he looks like he's standing (try a few frames, starting at 2). Create another state (with both enter and exit methods) called Noticing and for now, just print out a message on the screen. Test your state machine by for example accepting two different keystrokes, one which enters the Pacing state by calling self.request('Pacing') from its handler and another that enters the Noticing state with self.request('Noticing').
  4. Making the Character Look:
    Now add to the actor the ability to face you when his self.is_looking member variable is set to True. Simply do this by creating a task called look and inside it call lookAt(base.camera) on the nodepath of the actor, but only if self.is_looking is True. Unfortunately the actor model is turned 180 degrees the wrong way, so we need to flip him over by then adding 180 degrees to his new heading (you can use getH and setH). Now set the self.is_looking variable to False when you enter the Pacing state and True when you enter the Noticing state. Test that this works (try approaching him from different directions). One problem that you may notice is that your character faces the wrong way once he resumes his pacing after having looked at you. You can fix this with a member variable that stores the facing angle of the previous pacing state. See if you can get it fixed that way.
  5. Triggering Transitions with Collisions:
    Let's have him change automatically from Pacing to Noticing when you approach him. You need to create two Collision Spheres. One under a new CollisionNode you create under your base.camera node, which you call 'avatar' and another under a new CollisionNode you create under your actor node, which you call 'sensor'. To refresh your memory, here is how you add a collision sphere to a new collision node:
    <colnodepath> = <modelnodepath>.attachNewNode(CollisionNode(<name>))
    <colnodepath>.node().addSolid(CollisionSphere(0,0,0,<radius>))

    Use a radius of 10 for the avatar sphere and 35 for the sensor sphere. Now that you have the two collision spheres set up, you need to create a collision handler that sends out the types of messages we want. Inside your World constructor, create a new CollisionHandlerEvent instance and then define these two event patterns:

    <collhandler>.addInPattern('%fn-into-%in')
    <collhandler>.addOutPattern('%fn-out-%in')

    Then set up the default collision traverser (base.cTrav) to use your avatar collision node (that you created above) as the from object and associate events its collision to the handler. Here's how that could be done:

    base.cTrav = CollisionTraverser('world traverser')
    base.cTrav.addCollider(self.avatar,<collhandler>)

    Inside you Character class, you can now accept the messages 'avatar-into-sensor' and 'avatar-out-sensor' that represent when the user enters the sensor sphere around the character and when he/she leaves the sphere, respectively. Create handlers for these messages (as methods of Character), which you can call approach_handler and leave_handler. In the former, you should have the character enter the Noticing state and in the latter the Pacing state. Make sure this works (remember you can make collision solids visible by calling the show() method on their nodes).

  6. Triggering Transitions with Selection:
    Let's have you be able to start talking to your character if you click on him while he notices you. To enabling the picking of 3D objects with your mouse, you can import the Picker class and simply initialize it inside your Character constructor like this:
    <mouse_picker>=Picker(<youractornodepath>)   
    <mouse_picker>.make_pickable(<youractornodepath>)

    Now, whenever you click on your actor, an event with the name 'clicked_render/Eve' occurs, which you can of course accept in your Character class. See if you can make your character respond to your clicking.

  7. Starting a Conversation:
    Create a new state called Conversing and enter that state when you click on your character in the Noticing state. Make sure the click is only received if the character is actually in the Noticing state (hint: you'll need to use the ignore method as well as the accept method). Similarly, only in the Conversing state should you receive the 'clicked_None' event (when user clicks on nothing) and that should send the character back to Pacing. As for what happens in the Conversing state, you can use OnscreenText to display a greeting while you are in this state (and remove it when you exit the state). Verify that the behavior of your character is following the original state diagram.
  8. Simple Conversation Machine:
    Instead of just showing a greeting when you enter the Conversing state, let's start an actual dialog! Use the "FSM with input" method (and a single defaultFilter) to create a new Conversation class that handles the branching dialog shown in this diagram:
    The diagram shows the state names in the blue boxes and the text that should shown on the screen when entering each state. The user picks response '1' by pressing the '1' key on the keyboard, which then takes the conversation to the state connected by the arrow labeled '1'. Same for '2'. The simplest way to do this, is to have the new class (that inherits from FSM.FSM) accept '1' and '2' as keyboard events, which are handled by the same handler method that directly calls the self.request(<input>) method for advancing to the next state.
/var/www/ailab/WWW/wiki/data/pages/public/t-vien-08-1/lab_5_materials.txt · Last modified: 2008/02/07 10:52 by hannes