Datasheet

Chapter 1: Understanding Flash3D

Creating a Parametric Particle System (Torus Worm)

In the previous section, you learned how to get a single element orbiting a torus using the parametric

equations of a torus. Here, you multiply that single element by 100 and create a parametric particle

system, which orbits (or worms around) your torus.

You get a more formal treatment of particles in the “ Gaming ” section of this book. But for the most

part, anything with more than one element can be treated as a particle system. Treating elements as

particles has a number of advantages. Primarily, particles are easily handled mathematically.

You ’ ll use particle systems extensively throughout this book.

Building a particle system in Flash is relatively easy, and in this section, you cover the basics. To build

the orbiting worm around a torus (parametric particle system), follow the steps below:

1. Declare the number of particles to be created and create an array to place your particles in. This

is the key to working with particles. Using the array “ particles_ary ” you ’ re able to control

position, color, and alpha of each particle.

var numOfParticles:uint = 100;

var particles_ary:Array = [];

2. Use a “ for ” loop to run the updateStage() function, which creates your particles. Once the

particles are created run the addEventListener method, which starts updating the loop for each

particle on every frame event.

for(var i:uint = 0; i < numOfParticles; i++)

{

updateStage();

numVar++;

//Start Looping

if(numVar==numOfParticles){

addEventListener(Event.ENTER_FRAME, myonEnterFrame);}

}

3. Draw your balls (particles) to the stage and place them in a particle array. A random color is

assigned to each ball using the Math.random()*0xffffff method.

//Draw a Ball

var ball:Sprite = new Sprite

//Assign a random ball color

ball.graphics.beginFill(Math.random()*0xffffff);

//draws your ball at 0,0

ball.graphics.drawCircle(0, 0, ballRadius);

ball.graphics.endFill();//ends the fill

//Add ball to the stage

addChild(ball);

//Push the ball into a particle array

particles_ary.push(ball);

4. With each onEnterFrame loop you update all your particle positions using myAngle+i/20

that separates the different particles in angle by the ratio of i/20. This causes your particles to

line up on the torus and move across its surface as the myAngle variable is iterated. Use the

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