Arquivos Development - Paulo Barbeiro

Panda3D gamedev tutorial 4

In this tutorial, we will see how to work with simple physics simulations in Panda3D’s built in physics engine. This simulations will be applied in our avatar movement, and ability to jump. Also we will explore briefly, Panda3D’s Interval features.

This tutorial aims to show how to use in a simple way, a physics engine. Just in case you are interested in learn about the use of ODE in Panda, check out this tutorial: http://paulobarbeiro.com.br/blog/?p=77&lang=en, it might be helpful.

Bad news guys! A good amount of all our logic will be lost! Most of all the logic related to the avatar’s movement, described in previous tutorials, will no longer work with physics simulation. I hope that can teach you something: Do not feed emotional feeling to your code! 🙂 And think well if you want to use physics or not, because the code will not be the same!

The work in this tutorial will be a bit long. And to make it easy to understand, we will talk a bit about physics engines, and how to implement them, afterwards, we will implement our code.

Physics Engines ——————-

Physics engines are softwares dedicated to perform physics calculus, usually Newtonian physics, to many different applications, and games is one of them.

These game engines, has one single work: calculate physics. That’s all! Physics engines, do not render screens, do not capture user inputs, do not synthesize audio. They just perform calculus, based on physic formulas.

Each engine has a certain number of formulas, it’s up to you choose the engine based on the features you will need.

So, how they work? how to use them on games?

Till now, in our tutorials, we had change our avatar’s coordinates values in order to simulate it’s movements. To move the avatar towards the right side, we have incremented it’s x position. And this is an absolutely acceptable approach, as far as we do not concern to realistic movements.

Any one can see that our avatar, falls at a constant speed. Which is not a realistic fall. In our universe, gravity speeds up the fall. In order to achieve more realistic results, implement physics simulation is crucial.

So, what change when some physics engine is implemented? We do not touch the object coordinates! When some physics engine is been used, we think about movements as a result of forces been applied to the objects! That means: to an object move towards right, a force, pointing to right, must be applied to this object. And all the jobs is upon the engine. The object movement, will be a result of physics calculus, performed by the engine. Our job will be select, and calibrate the forces that will be applied.

Think in movement as a result of applied forces isn’t hard. But it demands a little knowledge, of how to describe this forces mathematically: Vectors. Everybody knows that! We all studied this subject at the school, is just a matter to remember! This link might help a little bit.

There are a huge number of content about vectors, vector operations, forces, vector forces, on internet, just google it!

Now, we have seen a bit of concepts in physics engines usage. Let’s see, conceptually, how to apply this concepts in our game.

Till now, our avatar moves in three directions: left, right, down. So, to make our avatar move in this directions, by forces, we will have:
– down: gravity force;
– right: a push force towards right;
– left: a push force towards left.

In case we want a jump, a push force towards up, will be needed. See the graph bellow:

The graph above, shows the forces we will use, and their vector representation. For example, the gravity: Vec3(0,0,-9.81).
Those vector values, are XYZ “coordinates”. I gravity case: x=0, y=0, z=-9.81; that means, gravity pushed down, with 9.81 intensity (in Newtons).

In this tutorial, all forces are pointing to simple directions. See bellow:
– pushRight: Vec3(10,0,0): points to rightwards (x positive), intensity 10
– pushLeft: Vec3(-10,0,0): points leftwards (x negative), intensity 10
– pushUp: Vec3(0,0,20): point upwards (z positive), intensity 20

In our code, we will implement the basic Panda3D’s built in engine. During this process, we will see, how to implement the basic elements, and logic solution for problems.

Let’s start the first step. In Panda-tut-00.py file, we won’t change it much. In this main file, we just import and initialize the PhysicsCollisionHandler, which will be responsible for collision detections.

[code lang=”python”]
from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)

import direct.directbase.DirectStart
from pandac.PandaModules import *

from direct.task.Task import Task
from direct.showbase.DirectObject import DirectObject

from avatar import Avatar

#game class
class Game(DirectObject):
def __init__(self):
#init collider system
traverser = CollisionTraverser()
base.cTrav = traverser
base.cTrav.setRespectPrevTransform(True)

base.pusher = CollisionHandlerPusher()
base.pusher.addInPattern(“%fn-into-%in”)
base.pusher.addOutPattern(“%fn-out-%in”)

base.physics = PhysicsCollisionHandler()
base.physics.addInPattern(“%fn-into-%in”)
base.physics.addOutPattern(“%fn-out-%in”)
base.enableParticles()

#load platform model
self.plataforma = loader.loadModel(“../assets/eggs/plataformaBase”)
self.plataforma.reparentTo(render)
self.plataforma.setPos(0,10,0)
#load background sky
self.wall = loader.loadModel(‘../assets/eggs/papelParede’)
self.wall.reparentTo(render)
self.wall.setScale(1)
self.wall.setPos(-5, 30, -2)
#avatar
avatar = Avatar()
avatar.setCollision(traverser)

game = Game()
run()
[/code]

Pay attention that in this code, we just add the lines 24, 25, 26, and 27. The PhysicsCollisionHandler works just like the other handlers, the mayor difference is that it requires the particle system activation (line 27). The CollisionHandlerPusher, will not work here, but I left those line, for you to compare handler pusher with handler physics.

Now in Avatar class, there ar lots of changes! The code is presented below, and than the explanations.

avatar class code
[code lang=”python”]
from direct.showbase.DirectObject import DirectObject
from direct.actor.Actor import Actor
from direct.task import Task
from pandac.PandaModules import *
from direct.interval.IntervalGlobal import *

#modulo da classe Avatar
class Avatar(DirectObject):
def __init__(self):
self.persona = render.attachNewNode(‘persona’)

self.personaActorNode = ActorNode(‘personaActorNode’)
self.personaActorNode.getPhysicsObject().setMass(35)
self.personaActorNP = self.persona.attachNewNode(self.personaActorNode)
base.physicsMgr.attachPhysicalNode(self.personaActorNode)

self.personaActor = Actor(‘../assets/eggs/personagem.egg’,
{‘idle’:’../assets/eggs/personagem-parado’,
‘run’ :’../assets/eggs/personagem-correr’,
‘jump’:’../assets/eggs/personagem-pular’}
)
self.personaActor.setScale(1)
self.personaActor.setPos(0,0,5)
self.personaActor.reparentTo(self.personaActorNP)

self.persona.setPos(0,10,10)
self.persona.setScale(.15)
self.persona.setH(90)

self.state = { ‘left’ :False,
‘right’ :False,
‘ground’:False,
‘canJump’ :False
}

taskMgr.add(self.movement, “Avatar Movement”)

#timer for jump
self.startCallforJump = 0
self.timer = LerpFunc(self.performJump,
fromData = 0,
toData =1,
duration = 0.25,
blendType=’easeIn’,
extraArgs=[],
name=None)

#capture keyboard events
self.accept(‘arrow_left’, self.changeState, [‘left’,True])
self.accept(‘arrow_left-up’, self.changeState, [‘left’,False])
self.accept(‘arrow_right’, self.changeState, [‘right’,True])
self.accept(‘arrow_right-up’, self.changeState, [‘right’,False])
self.accept(‘space’, self.changeState,[‘jump’,True])
self.accept(‘space-up’, self.changeState,[‘jump’,False])
#capture collision events
self.accept(‘bola0CN-into-plataforma’, self.changeState, [‘ground’,True ])
self.accept(‘bola0CN-out-plataforma’, self.changeState , [‘ground’,False])

#Persona physics forces
self.pushUp=LinearVectorForce(0,0,20)
self.pushUpFN = ForceNode(‘pushup-force’)
self.pushUpFNP = render.attachNewNode(self.pushUpFN)
self.pushUpFN.addForce(self.pushUp)

self.pushLeft=LinearVectorForce(-10,0,0)
self.pushLeftFN = ForceNode(‘pushleft-force’)
self.pushLeftFNP = render.attachNewNode(self.pushLeftFN)
self.pushLeftFN.addForce(self.pushLeft)

self.pushRight=LinearVectorForce(10,0,0)
self.pushRightFN = ForceNode(‘pushright-force’)
self.pushRightFNP = render.attachNewNode(self.pushRightFN)
self.pushRightFN.addForce(self.pushRight)

self.gravityFN=ForceNode(‘world-forces’)
self.gravityFNP=render.attachNewNode(self.gravityFN)
self.gravityForce=LinearVectorForce(0,0,-9.81) #gravity acceleration
self.gravityFN.addForce(self.gravityForce)

base.physicsMgr.addLinearForce(self.gravityForce)

def setCollision(self, trav):
#colision nodes and solids
self.ball0 = CollisionSphere(0,0,1.5,1.5)
self.ball0NP = self.personaActorNP.attachNewNode(CollisionNode(‘bola0CN’))
self.ball0NP.node().addSolid(self.ball0)
self.ball0NP.show()

base.physics.addCollider(self.ball0NP, self.personaActorNP)
base.cTrav.addCollider(self.ball0NP, base.physics)

def movement(self, task):
#print self.personaActorNode.getPhysical(0).getLinearForces()
if(self.state[‘left’] == True):
if(len(self.personaActorNode.getPhysical(0).getLinearForces()) == 0):
self.personaActorNode.getPhysical(0).addLinearForce(self.pushLeft)
else:
self.personaActorNode.getPhysical(0).removeLinearForce(self.pushLeft)

if(self.state[‘right’] == True):
if(len(self.personaActorNode.getPhysical(0).getLinearForces()) == 0):
self.personaActorNode.getPhysical(0).addLinearForce(self.pushRight)
else:
self.personaActorNode.getPhysical(0).removeLinearForce(self.pushRight)

return Task.cont

def changeState(self, key, value, col=None):
if(self.state[‘canJump’] == True and key == ‘jump’):
if(value==True):
self.startCallForJump = globalClock.getRealTime()
if(value == False):
preparationTime = globalClock.getRealTime() – self.startCallForJump
if (preparationTime > 0.4): preparationTime = 0.4
elif(preparationTime 0):
self.personaActorNode.getPhysical(0).removeLinearForce(self.pushUp)
[/code]

Lets start in function __init__(self):

The first change here is to add an ActorNode to our avatar’s nodes structure. The ActoNode class is a special node class to be used in physics system. Do not confuse ActorNode with Actor class, which is used to play animation in rigged models.
First we create an ActoNode (line 5), than it’s mass is set; The ActorNode is attached to persona node, and the nodepath resulted is attached to physics handler.
Pay attention to another important detail, in line 17: the personaActor node (our model node), is attached to the ActorNode. This link will make the model move according physics simulations.

In lines 39 and 40, there is one variable and one function, that are gonna be used for avatar’s jump. More about it soon.
In lines 53 and 54, we capture the user input in space bar.

In lines 60 till 80, the forces to be applied in our avatar are set. In line 71, one of the forces is been applied, the gravity.

The forces are created as a vector force, the class LinearVectorForce, that contains the force direction and intensity. Also a ForceNode, attached to render, is needed.

The setCollision function:
Not much changes here. Note that now, collisionNodes are linked to PhysicsCollisionNode.

The movement function:
Here we have the logic that moves the avatar to left or right. Basically, the avatar state changes with user input, than this function applies the forces according this state changes. The methods addLinearForce() and removeLinearForce(), are pretty much self-explanatory, are they?

The changeState function:
In this function there is a special logic to avatar’s jump.
The avatar will perform the jump, when user releases the space bar, and the power of the jump, will vary depending on the time the user held the bar pressed.
When space bar is pressed the function evaluates if the avatar can jump (canJump = if the avatar is on the platform). Than the function evaluates if the key were pressed or released; If the key was pressed, the function stores the moment when the key was pressed; If the key was released, the function calculates the time it was pressed, than this value divides a value of 1000, than the result of such division is applied to the pushUp force, and finally a timer, that applies and removes, is started.

The performJump function:
This is a LerpFunction declared in line 40. This function is a sort of timer, that is used to apply the force, and in the next moment, remove it. A human jump, just like any other terrestrials animals, are resulting of one strong force application in one single moment. That is the reason the pushUp force must be removed so soon.

Conclusion??
Well, a simple conclusion?? You don’t need to use physics simulation if the resulting movement is not pleasing you! Physics is just another option! But, get yourself used to them. As more you know them, and better you apply the forces, better the results will look!

Panda3D gamedev tutorial 2

In this second tutorial we will create our avatar, and set up some Panda3D features for interaction: tasks and user inputs.
In Python code, we will see how to work with python modules, some conditionals and dictionaries.

Why is this python module necessary? Well, our code will start growing in size, and keeping classes in different files are really good to make our development easier. And this is a very easy thing to do: just open a new code file into our Panda-project/src folder named avatar.py, and let’s start with a very simple code for it:

[code lang=”python”]
from direct.showbase.DirectObject import DirectObject
from direct.actor.Actor import Actor

#modulo da classe Avatar
class Avatar(DirectObject):
def __init__(self):
self.persona = render.attachNewNode(‘persona’)
self.personaActor = Actor(‘../assets/eggs/personagem.egg’,
{‘idle’:’../assets/eggs/personagem-parado’,
‘run’ :’../assets/eggs/personagem-correr’,
‘jump’:’../assets/eggs/personagem-pular’}
)

self.personaActor.setPos(0,0,4.6)
self.personaActor.reparentTo(self.persona)

self.persona.setPos(0,10,0)
self.persona.setH(90)
self.persona.setScale(.1)
[/code]

Let’s see the new things in this code:
1 – from direct.actor.Actor import Actor
::> this is the Panda3D class, that deals with rigging animated models, which is the avatar female 3D model.

2 – self.persona = render.attachNewNode(‘persona’)
::> here we create a new node, that will host the model node. We will need this, because in future, we will add some other sub-nodes, and let’s keep them organized.

3 – self.personaActor = Actor(‘../assets/eggs/personagem.egg’,
::> in this lines, we create our Actor, based on our personagem.egg model file.

4 – {‘idle’:’../assets/eggs/personagem-parado’,
‘run’ :’../assets/eggs/personagem-correr’,
‘jump’:’../assets/eggs/personagem-pular’}
)
::> in this lines we inform our Actor class, which animations we want to load. This is a Python dictionary. You can notice ‘idle’ is a key, and ‘../assets/eggs/personagem-parado’ is the value. That means we want the ‘idle’ animation to be the animation in the “personagem-parado.egg” file. This is repeated to all animations we need.

5 – self.persona.setH(90)
::> this is a command to rotate the avatar. Try to comment this line, and see what happens.

To make easier to understant what is going on, take a look at the image below, to see how the Avatar’s nodes are organized:

So, what we have, is a personaActor node, linked to persona node. The personaActor node will host our 3D model, linked to persona, and positioned a little above the persona node.

The next image show how is organized our whole graph til now:

Now we need to import this module into the main file, Panda-tut-00.py, take a look:

[code lang=”python”]
from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)

import direct.directbase.DirectStart
from pandac.PandaModules import *

from direct.task.Task import Task
from direct.showbase.DirectObject import DirectObject

from avatar import Avatar

#game class
class Game(DirectObject):
def __init__(self):
#load platform
self.platform = loader.loadModel(“../assets/eggs/plataformaBase”)
self.platform.reparentTo(render)
self.platform.setPos(0,10,0)
#background
self.wall = loader.loadModel(‘../assets/eggs/papelParede’)
self.wall.reparentTo(render)
self.wall.setScale(1)
self.wall.setPos(-5, 30, -2)

#avatar
self.avatar = Avatar()

game = Game()
run()
[/code]

At the end we will have a screen more or less like that.
From now on, all code relative to our avatar object, will be written in this module avatar.py. Let’s start creating a very simple and imperfect logic. It’s gonna be imperfect for games, and we’ll need to correct it in future, but is good enough for educational purpose. The logic will folow this rules:

– avatar falls, if it is not in contact with the platform;
– when avatar is in contact with the platform, it can moves to right or left;
– when user presses the left, or right key, the avatar chages position;

For that small logic, we’ll need a function to whatch for avatar’s states, and decide, when move the avatar. We will need avatar states as well!
Also, we will have a TASK! Tasks are functions used in Panda3D, which refer to: “The need to provide for certain game objects, execution loops.” It means, task allows us to create calls for functions every single frame! For further details take a look here!

The code for avatar module will be like that:
[code lang=”python”]
from direct.showbase.DirectObject import DirectObject
from direct.actor.Actor import Actor
from direct.task import Task

#module Avatar
class Avatar(DirectObject):
def __init__(self):
self.persona = render.attachNewNode(‘persona’)
self.personaActor = Actor(‘../assets/eggs/personagem.egg’,
{‘idle’:’../assets/eggs/personagem-parado’,
‘run’ :’../assets/eggs/personagem-correr’,
‘jump’:’../assets/eggs/personagem-pular’}
)
self.personaActor.setScale(.3)
self.personaActor.setPos(0,0,1.5)
self.personaActor.reparentTo(self.persona)

self.persona.setPos(0,30,0)
self.persona.setH(90)

self.state = { ‘flying’:True,
‘left’ :False,
‘right’ :False
}

taskMgr.add(self.movement, “Avatar Movement”)

def movement(self, task):
if(self.state[‘flying’] == True):
self.persona.setZ( self.persona.getZ() – 0.1 )
return Task.cont
[/code]

What’s new here:
1 – A state dictionary: self.state = {‘flying’:True, ‘left’:False, ‘right’:False}
::> It will host information of the current state of the avatar, which is gonna be watched for actions. The ‘flying’ state is the only one set as True, because at the very begining the avatar is out of the platform.
2 – We have a task manager: taskMgr.add(self.movement, “Avatar Movement”)
::> In this task manager, we’ve set the function self.movement to be called ate every single frame, and it is named as “Avatar Movement” task.
3 – A new function: def movement(self, task):
::> That is the function called by task manager.
Once this function is used by the task system, it must receive a ‘task’ argument, and return a Task constant, in this case Task.cont, which means we want the task manager keep calling this function.
Also, we have a simple logic inside this function. This logic evaluates is the state ‘flyign’ is true, in case yes, it changes the persona’s Z position, giving the illusion the avatar is falling.

But at this moment, running this code, you will see that the avatar falls none stop! So let’s make it to stop falling when it hits the platform’s z position. Bellow you will see the new movement function:

[code lang=”python”]
def movement(self, task):
if(self.state[‘flying’] == True):
self.persona.setZ( self.persona.getZ() – 0.1 )
if(self.persona.getZ() < -2.25):#condition to set ‘flying’ to False
self.state[‘flying’]=False
[/code]

This change in code, makes the flying state be set to False, when the persona’s z position hit the value -2.25, and than it stops falling, because if ‘flying’ state is not True, it position in z axis will not me chaged.

Now we have a very simple example about how create some logic based on boolean and integer values. Soon, this code will be changed in order to solve some issues.

User Inputs ————
Let’s add User Inputs, to allow the user to move the avatar sideways according directional keys are pressed. You can see more details about user inputs here.

In Panda3D user inputs are events sent throughout the system, in order to use them we need:
– declare which object must be notified, when certain events occur: accept()
– define functions to execute the actions we want.

Take a look the changes in avatar code, let’s talk about it latter:

[code lang=”python”]
from direct.showbase.DirectObject import DirectObject
from direct.actor.Actor import Actor
from direct.task import Task

self.smiley = loader.loadModel(‘smiley’)
self.smiley.reparentTo(self.persona)
self.smiley.setPos(0,0,0)
self.smiley.setScale(.2)

self.persona.setPos(0,10,0)
self.persona.setScale(.15)
self.persona.setH(90)

self.state = { ‘flying’:True,
‘left’ :False,
‘right’ :False
}

taskMgr.add(self.movement, “Avatar Movement”)

def movement(self, task):
if(self.state[‘flying’] == True):
self.persona.setZ( self.persona.getZ() – 0.1 )
if(self.persona.getZ() < -2.3):
self.state[‘flying’]=False
#move sideways
else:
if(self.state[‘left’]):
self.persona.setX( self.persona.getX() – 0.1 )
elif(self.state[‘right’]):
self.persona.setX( self.persona.getX() + 0.1 )
return Task.cont

def changeState(self, key, value):
self.state[key] = value
[/code]

The new things here take place bellow line 34.
In lines 35, 36, 37 and 38, we inform Panda3D, that our avatar must be notified when left and right arrow are pressed (‘arrow_left’ / ‘arrow_right’) and released (‘arrow_left-up’ / ‘arrow_right-up’).
Lately, the function self.changeState is set as the function that will be called every time the avatar is notified that the event did occur. In addition python lists ([‘left’,True], [‘left’,False], [‘right’,True] and [‘right’,False]) are sent to the function as parameters.

The changeState function task is very simple: change the avatar state.
The function is prepared to receive two arguments, key and value, that relates to the python dictionary keys and values. So the key argument, will always be a string (‘left’, ‘right’, or even ‘flying’), and the value argument will alway be a boolean value. Pay attention that these parameters are the python lists defined in self.accept command ( [‘left’, True] … [‘right’,False])

To finish this logic up, and make possible the avatar change it’s position on screen, in movement function, there is a logic that evaluates when the state[‘left’] or state[‘right’] are True, in order to change persona node position along X axis.

Yes!! We have interactivity! Really bad interactivity, but it works.

Collisions ———-
In the next post, we will improve a lot our code!
As you can see, we have a huge problem: our avatar passes through our objects!
To solve that, we must implement collisions.
WARNING: in next implementations, our code will gain a lot of complexity.

Panda3D gamedev tutorial 1

This is the first post about game development in Panda3D. (version 1.6)

My idea is to introduce people in game development, I have chosen Panda3D as game engine, because it is a great software, free and multi-platform.

In order to start following these tutorials, you will need to download some files, and follow some instructions about how organize the files. Here is the link.

The goal here is to build a very simple game: A girl, in a futuristic scenario, who needs to avoid some barriers and traps.

I hope you already have Panda3D 1.6.2, otherwise, go to www.panda3d.org, download and install it. (There is some issue with MacOSX version, check forum to find solutions)

… let’s start.

To start writing Panda3D code all you need is a simple text editor, Microsoft Word or Open Office Writer do not work for this!
In case you work on Linux, Gedit is great!
In case you work on Mac, Xcode is… is ok, but…
In case you work on Windows, you should try Notepad++

But for all, I suggest Eclipse with python plugin (you can download Eclipse for PHP), it is a bit hard to setup, but it worth the effort.

So… if you are ready, let’s go and write some code. Start a new file, we could name it as Panda-tut-00.py, and write the following code:

[code lang=”python”]
import direct.directbase.DirectStart

run()
[/code]

This is the most simple code we can write to test if Panda3D is working!
The first line imports the DirectStart class, that starts Panda3D basic systems, and creates the screen where our game is gonna happened.
The line run(), basically starts the Panda3D main loop. Every game needs a main loop. The main loop, is a magical stuff that will give our game the “Frames”! And thanks for the frames per second, we can change game objects position in time, and all the magic is possible.

In order to run this simple code you have to:

In case you work on Linux (you know what to do, but…), you go to the Terminal, navigate to Panda-project/src folder, and run: python Panda-tut-00.py
In case you work on Mac (I think you know what to do…), you go to the Terminal, navigate to Panda-project/src folder, and run: python Panda-tut-00.py
In case you work on Windows (ohh… dear Lord, that God have mercy of your soul!)… You need to remember how to navigate using the Command Prompt, and the command ‘cd’. To start Command Prompt, go to Start menu >> All Programs >> Accessories >> Command Prompt, and navigate till the Panda-project/src folder, and run the command: python Panda-tut-00.py

…and that’s how you are gonna run and test, all our codes! You must know this process by heart!

Ok… let’s start for real!

Let’s start a real code… the previous was just to lay down some basis. Let’s start loading our scenario, our arena:

[code lang=”python”]
from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)

import direct.directbase.DirectStart
from pandac.PandaModules import *

from direct.task.Task import Task
from direct.showbase.DirectObject import DirectObject

#game class
class Game(DirectObject):
def __init__(self):
#load platform model
self.platform = loader.loadModel(“../assets/eggs/plataformaBase”)
self.platform.reparentTo(render)
self.platform.setPos(0,10,0)

#load background sky
self.wall = loader.loadModel(‘../assets/eggs/papelParede’)
self.wall.reparentTo(render)
self.wall.setScale(1)
self.wall.setPos(-5, 30, -2)

game = Game()
run()
[/code]

After running this code, you should see some thing like this:

JUST TO REMEMBER: this is a computer code, so, none errors in typing are tolerated. One single wrong letter, might cause an error. Also, another common error occurs when Panda3D do not find the models, we are asking him to bring to the game! So… follow the instructions here.

Let’s see what we have done:

1 – Are you seeing that little number on top-right corner? Those are your frames per second! and the first two lines are responsible for it to appear:
[code lang=”python”]
from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)
[/code]

2 – Now we need to inform Panda3D, which “parts” of it we need for the job. Panda3D is very big tool, and we don’t need all of it’s parts all the time… so we are asking it to give us some of it’s tools:
[code lang=”python”]
import direct.directbase.DirectStart
from pandac.PandaModules import *

from direct.task.Task import Task
from direct.showbase.DirectObject import DirectObject
[/code]

3 – As we are good people, we will create our code using object oriented programming, it means that all our game objects will be created in deferent parts of code. To start with our own game logic, will be and object itself, for that we define a class for it:
[code lang=”python”]
class Game(DirectObject):
def __init__(self):

self.platform = loader.loadModel(“../assets/eggs/plataformaBase”)
self.platform.reparentTo(render)
self.platform.setPos(0,10,0)

self.wall = loader.loadModel(‘../assets/eggs/papelParede’)
self.wall.reparentTo(render)
self.wall.setScale(1)
self.wall.setPos(-5, 30, -2)
[/code]

4 – We must instantiate our game class, into an object, and run it:
[code lang=”python”]
game = Game()

run()
[/code]

Crucial point

At this point we must talk about what is going on inside the class Game. The Game class has an initialize function def __init__(self):
This function is called once when the object is been instantiated, so inside this function, we write all the code we need to set up or game object. At the moment, we just brought to the game our arena and a background. Let’s watch the self.platform.
First we tell Panda3D to load the “plataformaBase” model, and put it’s path into self.platform variable. Than, we reparent the platform to the ‘render’, and finally we give platform a position.

Why this is a crucial point? First because this is the basic step, to load whatever you want into the game. But above that, we must understand what is this ‘render’?

The ‘render’ object is Panda3D scene graph’s top node! Was that explanation enough for you? Greate! Skip to the next chapter. If that definition wasn’t enough for you, pay attention to the explanation.

First of all, what is a scene graph? A scene graph is a structure to organize hierarchically the elements of a scene.

Almost all graphic softwares I know use a scene graph. Basically a scene graph starts with a main object, which points to other objects that are included into the scene. Such structure is used to optimize rendering processes, comunications among elements, collisions, etc. Take a look at this link, and this one!
Basically any object we want to appear in the game scene, must be some how linked to the scene graph. This object can be linked straight to the “render” node, or linked to an object which must be linked to “render”.

Each element we add to the scene graph, we create a Node and a NodePath. The node is created into the scene graph, and the path to this node (nodepath) is stored into a variable we name, in python code. Node and nodepaths, are not the same thing, but in Panda3D, nodepaths are much more used than the node itself. So, when the code says : self.platform = loader.loadModel(“../assets/eggs/plataformaBase”), Panda3D, loads a model, and creates a scene graph node, and save a path to this node in the self.platform variable.
Latter, in order to make this model visable, it’s necessary to link this new node to the render: self.platform.reparentTo(render).

Well, the “render” is the top node on Panda3D scene graph, and it is the center, the origin point of Panda3D’s coordinates system. So, after having the model imported, and linked to the scene graph, we can set a position to it: self.platform.setPos(0,10,0)

This process is repeated to all objects we want to insert into the scene. At the end of this process, we will have a scene graph estructure like this:

ADVICE: mass around with object’s position, and it’s links:
– change the coordinates values in platform and wall objects;
– link the wall, to the platform: self.wallreparentTo(self.plataforma);
– change the coordinates again;
– link the platform to the wall, and change the coordinates again.
This will help you to understand better this subject in Panda3D.

Files for Panda3D tutorial

Below you will find the files for the Panda3D tutorials.

Panda-project (15Mb .zip format)

Organizing project files.

To the code files and the assets files work as expected, is required to organize them in a certain structured way, as illustrated below:

The role project must be inside a folder called Panda-project.

Down below Panda-project, there will be two folders assets and src. The assets folder will hold the art files for the project (models, textures, audio files, etc.). For that reason, this assets folder has three children folders: eggs, textures(texturas), audio(som) (the names are in Portuguese).

The src folder (src stands for source) is where we will save all our code files, named with .py extension.