Effects: Physics and Particles - JavaFX Special Effects - page 209

}
public override function stop():Void{
emitTimeline.stop();
}
}
The interesting thing about the class Fireball as shown in Listing 10-7 is that Fireball extends
Group , WorldNode , Particle , and Emitter . It extends Group so it can contain the FireParticles it
produces. It extends WorldNode and Particle because it is has to bounce around the screen, and these
interface classes provide that functionality. Lastly, Fireball extends Emitter , and it does this so its
Timeline — emitTimeline —will be started and stopped.
For the most part, Fireball is just like the other Emitters in this topic: It creates a particle that
animates in some way. Fireball is also much like the other nodes used with the physics engine. It
creates a Body that it uses in the method update to synchronize its location on the screen with its location
in the physics model.
Fireball adds some other features to the update method. For example, if the Fireball is off the
screen to the left, it is moved to the right side. And if it is off to the right, it will be moved to the left so it
will fly back onto the screen. This is why the fireballs wrap around the screen. If the Fireball is below a
certain level, it removes itself.
The update function also adjusts the location of the FireParticles the Emitter has created. This is
done to keep the location of the particles steady while the Emitter moves about the screen.
The particles created by Fireball are defined by the class FireParticle . Listing 10-8 shows the
implementation of FireParticle .
Listing 10-8. FireParticle.fx
public class FireParticle extends ImageView, Particle{
public-init var initialSteps:Integer;//number of steps until removed
public-init var startingOpacity = 1.0;
public-init var speed:Number;//pixels per step
public-init var fadeout = true;
public-init var direction = -90.0;
public-init var directionVariation = 10.0;
var deltaX;//change in x location per step
var deltaY;//change in y location per step
var stepsRemaining = initialSteps;
init{
smooth = true;
translateX -= image.width/2.0;
translateY -= image.height/2.0;
rotate = Math.toDegrees(Main.random.nextFloat()*2.0*Math.PI);
opacity = startingOpacity;
//random direction in radians
var startingDirection = direction + Main.randomFromNegToPos(directionVariation);