## 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 3

Collisions between objects in games, are an absurdly important point. Important because it is something crucial to game mechanics, and also for being a picky topic in computational terms. And this technical factor forces us to some reflections.

To calculate object’s collisions, with efficiency, involves a series of complex algorithms – which we will not get any deeper – that consume a lot of computational power. And in order to make this work possible in real time, is mandatory to simplify our object’s geometric descriptions. For example: In case we have a human head, collisions can not be calculated for every single head detail, like eyes, libs, cheek. We must simplify our head shape for a simples sphere, or tube, or some other very simple geometry shape. That is how collision can be calculated in real time.

These simple shapes, are called collision solids. Each game engine, has it’s own collision solids, and we must used them in this simplification process.
As an example, I made use of some spheres to describe a human body:

The image above, is just an example, this little project won’t need such description. At the moment we will need just one simple sphere close to our avatar’s feet, in order to detect collision between our avatar and the platform.

In Panda3D, we must set some objects required to collision calculations, the Collision Traverser, and the Collision Handler. Let’s add these objects, set some initial configuration, and solve the problems latter. Yes, we will face some issues! But all solvable.
First the file Panda-tut-00.py:

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

#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]

What’s new here:
– In function __init__(self), we created the collision traverser and the collision handler (base.pusher)
– When the avatar is created, we have the line: avatar.setCollision(traverser). Here is where the avatar starts to set it’s collision properties.

Now, the Avatar class:

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

#class 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(1)
self.personaActor.setPos(0,0,5)
self.personaActor.reparentTo(self.persona)

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”)

#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])

def setCollision(self, trav):
#colision nodes and solids
self.ball0 = CollisionSphere(0,0,1.5,1.5)
self.ball0NP = self.persona.attachNewNode(CollisionNode(‘ball0CN’))
self.ball0NP.node().addSolid(self.ball0)
self.ball0NP.show()

trav.addCollider(self.ball0NP, base.pusher)
base.pusher.addCollider(self.ball0NP, self.persona)

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]

What’s new here:
– At the first lines, we have: from pandac.PandaModules import * . Here the tools needed for collision detection are imported.
– Between function __init__ and function movement, we get function setCollision.
– In function setCollision two node were created as children of persona node.

setCollision function, is where avatar will gain it’s collision solid and a collision node, which is crucial to make collisions possible.

After this changes, you will see that the avatar will move in a very weird way through platform, but will be easy to realize that it is now creeping around the platform, in a very weird way, but that is the natural behavior of collision handler pusher, and we will fix it soon.

An import detail! SPECIALLY WHEN USING YOUR OWN 3D MODELS!!!

Til now, we set collision objects to our avatar, NOTHING WAS DONE TO CONFIGURE COLLISIONS FOR OUR PLATFORM!!
Actually, the plataforma.egg file were already configured for collisions, that’s why we did not configured it. Let’s take a look how it was made, and you will see how to make it in your own models.

We could set some collision solids for our platform, but for educational matter, I chose Collision Mesh. Collision Mesh, is how we can set our 3d model, as collision solid, with one limitation: your model must be simple and not concave!
So, with a simple and not concave 3D model in a 3D software, you must convert it to Panda3D format. After this process, you will have a .egg file, which is basically a structured text file like an XML, that you can open in any simple text editor, and modify it as you like. In order to make collisions with those .egg models we need to set the line <Collide>{Polyset keep descend} for each group.

The .egg structure is:
– first, information about materials in geometry;
– than a Group, is defined;
– the Group definition starts with it’s matrix (information about it’s position and rotation);
– than we have a list (Vertex Pool), with all vertices that make the geometry;
– finally, a list of the polygons made with the vertices listed above.

So the line <Collide>{Polyset keep descend}, must me included right down the group declaration. Take a look:

[code lang=”xml”]
piso {
{Polyset keep descend}
{
{
1.000000 0.000000 0.000000 0.000000
0.000000 11.226257 0.000000 0.000000
0.000000 0.000000 0.182287 0.000000
0.000000 0.000000 0.000000 1.000000
}
}
piso {
0 {
1.000000 11.226256 -0.182287
}
1 {
1.000000 -11.226257 -0.182287
}
[…]
22 {
-1.000000 11.226261 -0.182287
}
23 {
-1.000000 11.226257 0.182287
}
}
{
{ Material }
{ 0.000000 0.000000 -1.000000 }
{ 0 1 2 3 { piso } }
}
[ … ]
{
{ Material }
{ 0.000003 1.000000 0.000012 }
{ 20 21 22 23 { piso } }
}
}
[/code]

Back to implementation —————

Before start the implementation, let’s think about the CollisionHandlerPusher, and how collisions will fit out game.
As said before, the CollisionHandlerPusher, do not allow objects to pass through each other, so collision pusher, pushes the object back, or aside.

But another possibility with it is, generate collision events! Collision Handler Pusher, is a sub class of Collision Handler Event, so we can make event generation when objects collide.
In Panda-tut-00.py, lines 20 and 21, is the point where we set Collision Handler Pusher to generate collisions events.

Implementation —————

Now, our basic collision is set up, but we must work on some issues.
The first collision we have is our avatar hitting the platform. At the moment, we make it stop falling using a Z axis numeric clause. But to make it right, let’s make the collision, change our avatar state.

To start with, let’s kill lines 49 e 50, in avatar class:
[code lang=”python”]
if(self.persona.getZ() < -2.3):
self.state[‘flying’]=False
[/code]

We must change the self.state[‘flying’] to false, through collision between our sphere and the platform.
Now let’s create a new accept, for collision events:
[code lang=”python”]
self.accept(‘ball0CN-into-plataforma’, self.changeState, [‘flying’,False])
[/code]

In this line above, we say to Panda3D, to notify avatar when the ball0CN hits the ‘plataforma’. And the function self.chageState, will be called to treat the event.
To deeper understanding of this collision event generation, check this link.

But now we have a logic problem. All functions that deals with collisions, must receive the collision informations, as an argument. So we need to prepare our function to receive such argument. The problem lays on the fact that self.changeState, is also used to treat simple events (keyboard events), which do not demand and special argument. And if we insert a new argument in that function, and the function was called, and do not pass all required arguments, an error will be generated, and the software will be killed.

Fortunately, there is a trick to solve this problem in Python. We will insert a new argument in that function, but a default value will be set to it, in case nothing were passed to the function. In this case, let’s insert a new argument called ‘col’ (small version for ‘collision’), and give to it a default value of ‘None’ (null in python):
[code lang=”python”]
def changeState(self, key, value, col=None):
self.state[key] = value
[/code]

At the end of this process, run the program, and you will see that the avatar stops falling, thanks to collision detection. But we still have a problem, the avatar seems to slide over the platform! That is a effect of Handler Pusher. To solve this problem we will “hard” set our avatar X and Y position.
Take a look at the final 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 *

#class 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(1)
self.personaActor.setPos(0,0,5)
self.personaActor.reparentTo(self.persona)

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

self.state = { ‘flying’:True,
‘left’ :False,
‘right’ :False
}
self.lastXpos = 0;

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

#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(‘ball0CN-into-plataforma’, self.changeState, [‘flying’,False])
self.accept(‘ball0CN-out-plataforma’, self.changeState, [‘flying’,True])

def setCollision(self, trav):
#colision nodes and solids
self.ball0 = CollisionSphere(0,0,1.5,1.5)
self.ball0NP = self.persona.attachNewNode(CollisionNode(‘ball0CN’))
self.ball0NP.node().addSolid(self.ball0)
self.ball0NP.show()

trav.addCollider(self.ball0NP, base.pusher)
base.pusher.addCollider(self.ball0NP, self.persona)

def movement(self, task):
if(self.state[‘flying’] == True):
self.persona.setZ( self.persona.getZ() – 0.06 )
#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 )
else:
self.persona.setX(self.lastXpos)
if(self.persona.getY() != 10):
self.persona.setY(10)
return Task.cont

def changeState(self, key, value, col=None):
self.state[key] = value
if(value == 0):
self.lastXpos = self.persona.getX()
[/code]

Basically, in function movement, we check if avatar’s Y position is different than 10, if is true, we set it to 10. It will solve the avatar sliding in Y axis. But it still slide on X axis. To solve this, we create a variable lastXpos, which will position the avatar in the proper X position. When the avatar is in touch with the platform, and not moving to right or left, it will be positioned in lastXpos. This variable is updated, every time the avatar will stop moving: See function self.changeState, when the ‘value’ is 0(zero), the lastXpos is updated with the avatar’s current position.

## 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

#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.setScale(1)
self.personaActor.setPos(0,0,5)
self.personaActor.reparentTo(self.persona)

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”)

#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])

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.

## Vectors & Physics :: Gamedev Panda3D cookbook

Based on Daniel Shiffman’s essays (http://www.shiffman.net/teaching/nature/)

In order to simulate movements in games, basically we change object’s coordinates values along software’s execution cycles; The result is the illusion of motion.
There some classical way to change those coordinates:
– Simply change the values…;
– Calculating vectors and implement kinematics;
– Physics simulation;

sample 1:

[code lang=”python”]
from direct.showbase.ShowBase import ShowBase
from direct.task import Task

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)
self.taskMgr.add(self.taskFunction, “testing Task”)
self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)

def taskFunction(self, task):
print “Cube’s position is: “, self.cube.getPos()
self.cube.setX(self.cube.getX()+0.01)
return Task.cont

app = MyApp()
app.run()
[/code]

This first sample, show how to create a simple motion by simply changing this cube’s x coordinate value. Pay attention in function taskFunction, over there, the cube’s ‘x’ position is incremented in 0.01 each time the task is executed.

sample 2:

[code lang=”python”]

from direct.showbase.ShowBase import ShowBase
from direct.task import Task
from pandac.PandaModules import Vec3

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.vector_left = Vec3(-0.01,0, 0)
self.vector_right= Vec3( 0.01,0, 0)
self.vector_up = Vec3( 0 ,0, 0.01)
self.vector_down = Vec3( 0 ,0,-0.01)
self.main_vec = Vec3(0,0,0)

self.taskMgr.add(self.taskFunction, “testing Task”)
self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)

self.accept(‘d’, self.changeDirection, [self.vector_right])
self.accept(‘a’, self.changeDirection, [self.vector_left])
self.accept(‘w’, self.changeDirection, [self.vector_up])
self.accept(‘s’, self.changeDirection, [self.vector_down])

def changeDirection(self, direction):
self.main_vec = direction

def taskFunction(self, task):
self.cube.setPos(self.cube.getPos()+self.main_vec)
return Task.cont

app = MyApp()
app.run()

[/code]

This second sample, shows a very simple way to use vectors instead changing coordinates values. Let’s take a closer look on vectors now.

Vectors: ========================================
references:

When an object moves through out a space, there is a very handing way to represent this motion: Vectors. That’s why you use vectors on all those physics equations on school! Vectors host key values to describe motion: Current position, motion direction, motion intensity, and even distances. Vectors might be 2D vectors and 3D vectors, well, theoretically vectors can have infinite dimensions, but let’s keep focus on game usage: 2D or 3D.

Let’s consider a rectangle moving around the screen. In a certain moment, this rectangle will have this description:
[quote]
Location – the point where the rect is now.
Speed – value that represents the distance the rect moves per time unity.
Acceleration – value that interferer on speed: increasing or decreasing it.
[/quote]
Note: This are all vectors, that might be 2D or 3D, depending on how many dimensions the space uses.

Technically loacation is a point, speed and acceleration are vectors, but for our purposes let’s use them all as vectors. Take a look at the next “pseudocode”, to see how location, speed and acceleration interacts to create a motion based on classic physics:

[quote]
speed = speed + acceleration
Location = location + speed
Than draw the thing on scene.
[/quote]

According this very simple algorithm, what we have: acceleration interfere on speed – speed interfere on location – to finish, we have to draw the thing on screen.

sample 3:
[code lang=”python”]
from direct.showbase.ShowBase import ShowBase
from direct.task import Task
from pandac.PandaModules import Vec3

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.vector_left = Vec3(-0.01,0, 0)
self.vector_right= Vec3( 0.01,0, 0)
self.vector_up = Vec3( 0 ,0, 0.01)
self.vector_down = Vec3( 0 ,0,-0.01)
self.main_vec = Vec3(0,0,0)

self.taskMgr.add(self.taskFunction, “testing Task”)
self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)

self.cubeSpeed = Vec3(0,0,0)
self.cubeAcc = Vec3(0,0,0)

self.accept(‘d’, self.changeDirection, [self.vector_right])
self.accept(‘a’, self.changeDirection, [self.vector_left])

def changeDirection(self, direction):
self.main_vec = direction

def taskFunction(self, task):
self.updateCube()
return Task.cont

def updateCube(self):
self.cubeAcc = Vec3(self.main_vec)
self.cubeSpeed += self.cubeAcc
self.cube.setPos( self.cube.getPos() + self.cubeSpeed )

app = MyApp()
app.run()
[/code]

The sample above, show how to implement vector kinematics on our previous vector sample. Pay attention on self.updateCube function, that small algorithm is there. In this sample you will notice that, as soon as you press ‘a’ ou ‘d’ key, the cube will begin move slowly, but it’s speed will increase fast. That happens because when acceleration is constant, the speed will increase at every instant, accumulating it’s previous values, and incrementing to it new acceleration additions.
To change this scenario compare to this code:

sample 3b:

[code lang=”python”]
from direct.showbase.ShowBase import ShowBase
from direct.task import Task
from pandac.PandaModules import Vec3

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.vector_left = Vec3(-0.01,0, 0)
self.vector_right= Vec3( 0.01,0, 0)
self.vector_up = Vec3( 0 ,0, 0.01)
self.vector_down = Vec3( 0 ,0,-0.01)
self.main_vec = Vec3(0,0,0)

self.taskMgr.add(self.taskFunction, “testing Task”)
self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)

self.cubeSpeed = Vec3(0,0,0)
self.cubeAcc = Vec3(0,0,0)

self.accept(‘d’, self.changeDirection, [self.vector_right])
self.accept(‘a’, self.changeDirection, [self.vector_left])

def changeDirection(self, direction):
self.main_vec = direction
self.cubeAcc = Vec3(self.main_vec)

def taskFunction(self, task):
self.updateCube()
return Task.cont

def updateCube(self):
self.cubeSpeed += self.cubeAcc
self.cube.setPos( self.cube.getPos() + self.cubeSpeed )
self.cubeAcc *= 0

app = MyApp()
app.run()
[/code]

A few differences here:
– Note that self.cubeAcc is define only when the key is pressed.
– Note that, self.cubeAcc is set to zero (at the end of function updateCube)

This small differences make the cube accelerates only when you press the keys, after that, the speed gets constant.

In practice, on vectors we have:
– positioning
– direction
– intensity

Those properties are very handy when we think about movements. Thanks to Python, we can calculate all that vectors easily, but that doesn’t happen very often in other languages. Usually we have to watch to vector operations in order to get different vectors, to use them in different motions… Probably the most used vector operation is vector subtraction. Usually we use vector subtraction, in order to make an object pursue another object, the magic happens because: When B vector is subtracted by A vector, the resultant C vector, points to B vector from A vector, with the same size as the distance between A and B.

The next sample shows an usage of this vector subtraction. A sphere goes moving from cube to cube calculating vector subtraction. All the work is in function update (inside Smiley class).

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

from direct.showbase.ShowBase import ShowBase
from direct.showbase.DirectObject import DirectObject
from direct.task import Task
from pandac.PandaModules import *

class Cube(DirectObject):
loc = Vec3(0,0,0)

def __init__(self, pos):
self.loc = pos
self.loadModels()

def loadModels(self):
self.cube = loader.loadModel(‘box’)
self.cube.setPos(self.loc)
self.cube.reparentTo(render)

# Class smiley ————————————
class Smiley(DirectObject):
loc = Vec3(0,0,1)
speed = Vec3(0,0,0)
acc = Vec3(0,0,0)
mass = 1
maxForce = 0.1

def __init__(self, pathToFollow):
self.loadModels()
self.way = pathToFollow
self.nextIt = 1;
self.next = self.way[1].loc
print “next pos: “, self.next

def loadModels(self):
self.smiley = loader.loadModel(‘smiley’)
self.smiley.setPos(self.loc)
self.smiley.reparentTo(render)

def update(self):
target = self.next
direction = target – self.loc
distance = direction.length()
direction.normalize()
direction *= self.maxForce

self.loc += direction
if(distance = len(self.way) ):
self.nextIt=0
self.next = self.way[self.nextIt].loc
self.smiley.setPos(self.loc)

#game Class —————————————
class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.box0 = Cube(Vec3(0,0,1))
self.box1 = Cube(Vec3(10,0,1))
self.box2 = Cube(Vec3(5,10,1))
self.box3 = Cube(Vec3(-10,10,1))
self.box4 = Cube(Vec3(-10,-5,1))
self.box5 = Cube(Vec3(0,-10,1))

self.wayPoints = (self.box0, self.box1, self.box2, self.box3, self.box4, self.box5)

self.smileyForce = 0.5
self.smiley = Smiley(self.wayPoints)

#code for floor
self.cm = CardMaker(“ground”)
self.cm.setFrame(-20, 20, -20, 20)
self.ground = render.attachNewNode(self.cm.generate())
self.ground.setPos(0, 0, 0)
self.ground.lookAt(0, 0, -1)

self.taskMgr.doMethodLater(4, self.update, “update task”)

# Set the camera position
base.disableMouse()
base.camera.setPos(15, -30, 20)
base.camera.lookAt(0, 0, 0)

self.fiatLux()

def update(self, task):
self.smiley.update()
return Task.cont

def fiatLux(self):

# Directional light 01
self.directionalLight = DirectionalLight(‘directionalLight’)
self.directionalLight.setColor(Vec4(0.95, 0.95, 0.8, 1))
self.directionalLightNP = render.attachNewNode(self.directionalLight)
# This light is facing backwards, towards the camera.
self.directionalLightNP.setHpr(45, -15, 0)
render.setLight(self.directionalLightNP)

game = MyApp()

run()
[/code]

Physics ========================================

In order to simplify physics simulations, game engines provide physics engines. In Panda3D, the default physics engine is ODE.
Those physics engines, do all the physics calculus, collisions, joints, and provide data to update our scene.

sample 4:
[code lang=”python”]

from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)

from direct.showbase.ShowBase import ShowBase
from direct.showbase.DirectObject import DirectObject
from direct.task import Task
from pandac.PandaModules import *

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.fiatLux()

#Create physics world
self.world = OdeWorld()
self.world.setGravity(0,0,-9.81)

#prepare for collisions
self.world.initSurfaceTable(1)
self.world.setSurfaceEntry(0, 0, 150, 0.0, 9.1, 0.9, 0.00001, 0.0, 0.002)

#create a space to allow collision events
self.space = OdeSimpleSpace()
self.space.setAutoCollideWorld(self.world)
self.contactgroup = OdeJointGroup()
self.space.setAutoCollideJointGroup(self.contactgroup)

#creates a floor in game scene, and physics world
self.cm = CardMaker(“ground”)
self.cm.setFrame(-20, 20, -20, 20)
self.ground = render.attachNewNode(self.cm.generate())
self.ground.setPos(0, 0, 0); self.ground.lookAt(0, 0, -1)
self.groundGeom = OdePlaneGeom(self.space, Vec4(0, 0, 1, 0))

#Creates a cube in game scene
self.box = loader.loadModel(‘../assets/eggs/box_c.egg’)
self.box.reparentTo(render)
self.box.setPos(0,9.5,7)
self.box.setHpr(5,35,57)
#self.box.setScale(1)
self.box.setColor(0.5, 0.5, 0.5, 1)

#creates a “body”: representation of the cube in physic world.
self.boxBody = OdeBody(self.world)
self.boxMass = OdeMass()
self.boxMass.setBox(100,1,1,1)
self.boxBody.setMass(self.boxMass)
self.boxBody.setPosition(self.box.getPos(render))
#print self.box.getQuat(render)
self.boxBody.setQuaternion(self.box.getQuat(render))
#print self.boxBody.getQuaternion()
#Creates a collision solid for the body
self.boxGeom = OdeBoxGeom(self.space, 2,2,2)
self.boxGeom.setBody(self.boxBody)

# Set the camera position
base.disableMouse()
base.camera.setPos(40, 40, 20)
base.camera.lookAt(0, 0, 0)

self.taskMgr.doMethodLater(4, self.update, “update task”)

def update(self, task):
#mandatory
self.space.autoCollide()
self.world.quickStep(globalClock.getDt())

#Update cube rendering, based on physics world data
self.box.setPosQuat(render, self.boxBody.getPosition(), Quat(self.boxBody.getQuaternion()))

#mandatory when you need collision events
self.contactgroup.empty()
return Task.cont

def fiatLux(self):

# Directional light 01
self.directionalLight = DirectionalLight(‘directionalLight’)
self.directionalLight.setColor(Vec4(0.95, 0.95, 0.8, 1))
self.directionalLightNP = render.attachNewNode(self.directionalLight)
# This light is facing backwards, towards the camera.
self.directionalLightNP.setHpr(45, -15, 0)
render.setLight(self.directionalLightNP)

game = MyApp()

run()

[/code]

In the sample above we have a very simple scene, a cube that falls, and hits a table, but all the motion is simulated by physics engine. The usage of physics engines demand some specific setups, and integration with rendering system, but all the hard work is made by the physics engine.

We also can simulate some forces been applied into objects!! like a kick on a ball; throw a stone; whatever you want… Let’s see a sample, when simulation starts, press ‘f’ key:

[code lang=”python”]

from pandac.PandaModules import loadPrcFileData
loadPrcFileData(”,’show-frame-rate-meter 1′)

from direct.showbase.ShowBase import ShowBase
from direct.showbase.DirectObject import DirectObject
from direct.task import Task
from pandac.PandaModules import *

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

self.fiatLux()

self.world = OdeWorld()
self.world.setGravity(0,0,-9.81)

self.world.initSurfaceTable(1)
self.world.setSurfaceEntry(0, 0, 150, 0.0, 9.1, 0.9, 0.00001, 0.0, 0.002)

self.space = OdeSimpleSpace()
self.space.setAutoCollideWorld(self.world)
self.contactgroup = OdeJointGroup()
self.space.setAutoCollideJointGroup(self.contactgroup)

self.cm = CardMaker(“ground”)
self.cm.setFrame(-20, 20, -20, 20)
self.ground = render.attachNewNode(self.cm.generate())
self.ground.setPos(0, 0, 0); self.ground.lookAt(0, 0, -1)
self.groundGeom = OdePlaneGeom(self.space, Vec4(0, 0, 1, 0))

self.box = loader.loadModel(‘../assets/eggs/box_c.egg’)
self.box.reparentTo(render)
self.box.setPos(0,9.5,7)
self.box.setHpr(5,35,57)
self.box.setColor(0.5, 0.5, 0.5, 1)

self.boxBody = OdeBody(self.world)
self.boxMass = OdeMass()
self.boxMass.setBox(100,1,1,1)
self.boxBody.setMass(self.boxMass)
self.boxBody.setPosition(self.box.getPos(render))
self.boxBody.setQuaternion(self.box.getQuat(render))
#collision solid in physics world
self.boxGeom = OdeBoxGeom(self.space, 2,2,2)
self.boxGeom.setBody(self.boxBody)

# Set the camera position
base.disableMouse()
base.camera.setPos(40, 40, 20)
base.camera.lookAt(0, 0, 0)

#press ‘f’ key
self.accept(‘f’, self.applyForce)

self.taskMgr.doMethodLater(4, self.update, “update task”)

def update(self, task):
#mandatory
self.space.autoCollide()
self.world.quickStep(globalClock.getDt())

#update rendering system
self.box.setPosQuat(render, self.boxBody.getPosition(), Quat(self.boxBody.getQuaternion()))

#mandatory for collision events
self.contactgroup.empty()
return Task.cont

def fiatLux(self):

# Directional light 01
self.directionalLight = DirectionalLight(‘directionalLight’)
self.directionalLight.setColor(Vec4(0.95, 0.95, 0.8, 1))
self.directionalLightNP = render.attachNewNode(self.directionalLight)
# This light is facing backwards, towards the camera.
self.directionalLightNP.setHpr(45, -15, 0)
render.setLight(self.directionalLightNP)

def applyForce(self):
print “apply force!”
print self.boxBody.getMass()
self.boxBody.setForce(100000,0,0)

game = MyApp()

run()

[/code]

## 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.

## Collisions :: Gamedev Panda3D cookbook

Detect collision between game objects is a crucial practice in (almost) any game. Beside collision detection, is also important to know what to do, when collisions occur.

Game engines, always provide collision detection features, and is very important to watch the “elements” used in this procedures.
Panda3D gives us:
– Collision handlers: out of the box behaviors to be use;
– Collision geometries (sphere, cube, plane, capsule, line, ray …);
– 3D mesh collisions;
– Collision events.

When a collision is detected, events are dispatched through out the system, and those events can be captured by game objects, and trigger some actions.

sample 1:

[code lang=”python”]
from direct.showbase.ShowBase import ShowBase
from direct.task import Task
from pandac.PandaModules import *

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

# Create a Traverser and Handlers: step one
base.cTrav = CollisionTraverser()
base.pusher = CollisionHandlerPusher()
base.pusher.addInPattern(‘%fn-into-%in’)

self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)

# create colliders: step two
self.cubeCSphere = CollisionNode(“cubeCSphere”)
self.cubeCSphere.addSolid( CollisionSphere(0,0,0, 1.05) )
self.cubeEsfNP = self.cube.attachNewNode(self.cubeCSphere)
self.cubeEsfNP.show()

# Point to the Traverser and to the Handler, which objects must be “watched” to capture it’s collisions: third step
base.cTrav.addCollider( self.cubeEsfNP, base.pusher )
base.pusher.addCollider( self.cubeEsfNP, self.cube )

self.smiley = loader.loadModel(‘smiley’)
self.smiley.reparentTo(self.render)
self.smiley.setScale(0.5);
self.smiley.setPos(3, 10, -1.5)

self.smileyCSphere = CollisionNode(“smileyCSphere”)
self.smileyCSphere.addSolid( CollisionSphere(0,0,0, 1.05) )
self.smileyEsfNP = self.smiley.attachNewNode(self.smileyCSphere)
self.smileyEsfNP.show()

self.taskMgr.add(self.taskFunction, “testing Task”)
self.accept(‘cubeCSphere-into-smileyCSphere’, self.collisionEvent)

def collisionEvent(self, entry):
print “Game objects did collide!!”
print entry

def taskFunction(self, task):
self.cube.setX(self.cube.getX()+0.05)
return Task.cont

app = MyApp()
app.run()
[/code]

In the sample above, a simple collision, between the cube and a smiley, is detected, and because a CollisionHandlerPusher were use as a collision handler, the objects do not cross each other. In addition, an event were dispatched, in order to trigger some action, in this case, an output with collision info were printed in the console.

Lets take a closer look at the Panda3D’s procedures steps:
1- Creation of CollisionTraverser and a CollisionHandler;
2- Creation of: CollisionNode and CollisionSolid;
3- Attach CollisionNodes and CollisionSolid to CollisionTraverser and CollisionHandler.

Steps:
Step 1:

# Creation of CollisionTraverser and a CollisionHandler: step one
base.cTrav = CollisionTraverser()
base.pusher = CollisionHandlerPusher()
base.pusher.addInPattern(‘%fn-into-%in’)

First thing, a CollisionTraveser is created; than, a CollisionHandler is created as a Pusher (the CollisionHandlerPusher do not allow game objects to pass through each other). In the third line, is added to the “Pusher”, an order to dispatch events when collisions occur.

Step 2:

# Creations of colliders: second step
self.cubeCSphere = CollisionNode(“cubeCSphere”)
self.cubeCSphere.addSolid( CollisionSphere(0,0,0, 1.05) )
self.cubeEsfNP = self.cube.attachNewNode(self.cubeCSphere)
self.cubeEsfNP.show()

This step is a bit more complicated.
Literally the code says:
– Create a collision node called “cubeCSphere”, and save the path to it, in the variable self.cubeCSphere;
– Add a collision solid sphere to the collision node “cubeCSphere”.
– Attach the collision node to cube node (self.cube), and save this node path in the variable self.cubeEsfNP.
– render the collision node (as a sphere were set as a collision solid, the engine will render a transparent sphere).

This commands are mandatory, except by the self.cubeEsfNP.show(), which serves only as a pre-view.

Observe that this steps must be set for each game object which will interact through collisions. For example, the smiley object also receives those collision nodes.

Step 3:

# Point to the Traverser and to the Handler, which objects must be “watched” to capture it’s collisions: third step
base.cTrav.addCollider( self.cubeEsfNP, base.pusher )
base.pusher.addCollider( self.cubeEsfNP, self.cube )

After setting the collision nodes (CollisionNode, steps 1 and 2), is absolutely required to inform the system how to deal with collisions.
The command: base.cTrav.addCollider( self.cubeEsfNP, base.pusher ), says the Traverser that collisions related to the collision node self.cubeEsfNP, must be treated by the handler “Pusher”.
The command: base.pusher.addCollider( self.cubeEsfNP, self.cube ), says to the “Pusher”, when collisions related to the collision node self.cubeEsfNP occurs, the “pusher” behavior, must be applied to the node self.cube.

This is a good example to be use in situations when objects can not pass through other objects, like an character can not pass through a wall.

The three steps we’ve seen thus far, show the basic set up for collisions in Panda3D. Now let’s see a interesting detail: how to dispatch events when collisions occur.

This is possible to be done in Panda3D, thanks to the CollisionHandlerEvent, that dispatches events when a collision is detected. The CollisionHandlerPusher is a subclass of CollisionHandlerEvent, as such, it inherits the collision events features.

When the CollisionHandlerPusher was created (step 1), pay attention at the command: base.pusher.addInPattern(‘%fn-into-%in’). This is the set up command that says to the Pusher, which patterns of collision can generate events.

See the line:
self.accept(‘cubeCSphere-into-smileyCSphere’, self.collisionEvent)
This line is the command used to capture events in the system, in this case, this event is gonna be generated by the Pusher when the cube collide into the smiley (‘cuboCEsfera-into-smileyCEsfera’), than we are gonna capture it, and do something in the self.collisionEvent function.

So, once the event is captured the function self.collisionEvent is called. Pay attention that when a collision event is captured, the function that deals with it, must be ready to deal with an argument “entry”, which gives you the many important informations about the collision itself, like coordinates, normals, etc.

sample 2:

[code lang=”python”]

from direct.showbase.ShowBase import ShowBase
from direct.task import Task
from pandac.PandaModules import *

class MyApp(ShowBase):

def __init__(self):
ShowBase.__init__(self)

# CCreation of CollisionTraverser and a CollisionHandler: step one
base.cTrav = CollisionTraverser()
base.event = CollisionHandlerEvent()
base.event.addInPattern(‘%fn-into-%in’)
base.event.addAgainPattern(‘%fn-again-%in’)
base.event.addOutPattern(‘%fn-outof-%in’)

self.cube = self.loader.loadModel(“box”);
self.cube.reparentTo(self.render)
self.cube.setScale(1)
self.cube.setPos(-3,10,-2)
# Create colliders: step two
self.cubeCSphere = CollisionNode(“cubeCSphere”)
self.cubeCSphere.addSolid( CollisionSphere(0,0,0, 1.05) )
self.cubeEsfNP = self.cube.attachNewNode(self.cubeCSphere)
self.cubeEsfNP.show()
#Point to the Traverser and to the Handler, which objects must be “watched” to capture it’s collisions: third step
base.cTrav.addCollider( self.cubeEsfNP, base.event )

self.smiley = loader.loadModel(‘smiley’)
self.smiley.reparentTo(self.render)
self.smiley.setScale(0.5);
self.smiley.setPos(0, 10, -1.5)

self.smileyCSphere = CollisionNode(“smileyCSphere”)
self.smileyCSphere.addSolid( CollisionSphere(0,0,0, 1.05) )
self.smileyEsfNP = self.smiley.attachNewNode(self.smileyCSphere)
self.smileyEsfNP.show()

self.taskMgr.add(self.taskFunction, “testing Task”)

#Capture Collision Events
self.accept(‘cubeCSphere-into-smileyCSphere’, self.collisionEventIN)
self.accept(‘cubeCSphere-again-smileyCSphere’, self.collisionEventAGAIN)
self.accept(‘cubeCSphere-outof-smileyCSphere’, self.collisionEventOUT)

def collisionEventIN(self, entry):
print “Objects did collide!!”
print entry

def collisionEventOUT(self, entry):
print “Objects did stop colliding!!”
print entry

def collisionEventAGAIN(self, entry):
print “Objects are still colliding!!”

def taskFunction(self, task):
self.cube.setX(self.cube.getX()+0.05)
return Task.cont

app = MyApp()
app.run()
[/code]

In this sample there is a demonstration of the usage of CollisionHandlerEvent. This collision handler do allow objects to pass through each other, so in this case, the cube will pass through the smiley with no problem.

The CollisionHandlerEvent, is a great way to create sensors around the game arena. For example, an avatar pass through a gate, and a trap is triggered.

Observe the changes in steps 1 and 3, and in the event capture set up.
The changes are small. The most import are when we create and when we capture the events. In this sample, not only we set up the ‘into’ event, but also we defined the ‘outof’ and the ‘again’.

Events “into”, occur when a game object collide into another.
Events “outof”, occur when game objects stop colliding each other.
Events “again”, occur when game objects are colliding.

## Events and Inputs :: GameDev Panda3D cookbook

Inputs and events are common elements in software development as a whole. A user input is usually some interaction method given to the user be able to command the software. It can be triggered by a key, a mouse click, a voice detection system, a touch on the screen.
Events are commands exchanged between elements of software. In the case of a game, we can imagine the following situation: A character is walking through a castle, where there is a trigger of a trap. When the character goes through the trigger, the trigger signals the trap to shoot arrows that will kill the character.
In this short description, we can say that the trigger sent a message to the trap shoot. This message is what we call events.

Both user inputs and events between objects have a vital role in game development.

Let’s see how to catch a keyboard event, in this case, when the ‘W’ key was pressed.

sample 1:

User Inputs in Panda3D, are sent to the system as events. When a key is pressed, an event message is sent throughout the system, what developer must do, is set an object to “listen” to a specific event.

This procedure is done in two steps:
1- Set the event which we are interested in: self.accept( ‘event name’, function)
2- Define a function to deal with the event. Basically, “what must be done, after the event were triggered”.

In the sample above, the event created by the pressure in ‘W’ key, is caught and treated by the function ‘catchKeyPressed’.

sample 2:

In this second sample, we have new possibilities: parameters, and event ‘up’.

The event ‘-up’, is used to catch the event generated when a key is unpressed.

EVENTS——————————

Events, like said before, are a way to make game object to talk with each other.
In general, there are two steps to make it happens:
1- Define which event an object needs to be aware of;
2- Give the commands to send the messages.

In Panda3D, user inputs are events, so we can catch events in the same way we configure user inputs.
Now, let’s see how to send some event.

sample 1:

When the ‘w’ key is pressed, a task is created, and the taskFunction is gonna make the cube move towards right. As soon as the cube x position be bigger than 3, an event is sent to the system (messenger.send( “stopCuboEvent”) ). This event is caught by our class and executes the stopCubeFunction, which deletes the task, and the cube stops.

## Published: Panda3D GE book

I just received my copy of the book 1.6 Panda3D game engine, by David Brian Mathews (published by Packt Publishing), which I was a technical reviewer.

The book is suited for anyone who’s starting to learn Panda3D.

The Panda3D engine is very simple to use and flexible. I started studying the Panda3D during my specialization studies, and its simplicity leads us to choose Panda3D in our final project.

The book written by David, is excellent, and easy to understand, although it requires a minimum understanding of programming and logic. But readers, newbies at the game development will easily understand the Panda3D’s tools described in this book, which I think, is the only publication about this game engine, apart from and some blog posts, and the official Panda3D’s guide, and docs.

Soon, I expect to write some posts about this book: some specifics topics for Mac and Linux; some ways to solve the problems posed in the book; and a tutorial on programming using Panda3D.