Effects: Physics and Particles - JavaFX Special Effects - page 210

var theta = Math.toRadians(startingDirection);
deltaX = Math.cos(theta)*speed;
deltaY = Math.sin(theta)*speed;
}
package function doStep(){
//remove particle if particle has expired
if (--stepsRemaining == 0){
delete this from (parent as Group).content;
}
//advance particle's location
translateX += deltaX;
translateY += deltaY;
if (fadeout){
opacity = startingOpacity*(stepsRemaining as Number)/(initialSteps as Number);
}
rotate += 4;
}
}
In Listing 10-8 we see the class FireParticle , which extends ImageView and Particle . This class
borrows many ideas from the particles in Chapter 2. We can see that the variable initialSteps
determines how long each FireParticle will be present in the scene, just like before. The other
parameters work as expected Note, however, that direction is preset to -90. This causes the
FireParticle to move upward like fire does. In the init function we can see that the variable
startingDirection is set to the value of direction plus a random value. This gives each FireParticle a
little variation in its motion.
The doStep method also works much as expected— when stepsRemaining reaches zero the
FireParticle is removed from the scene. The position of the FireParticle is updated by adding deltaX
to translateX and adding deltaY to translateY . Lastly, the opacity of the FireParticle is set based on
how far along the FireParticle is in its life cycle.
Summary
This chapter presented two examples of using particle effects with a physics engine. The first example
used a body for each particle. This created a complex effect, but at the expense of performance. The
second example used one body per emitter, and each emitter created its own small particle effect. Both
techniques are excellent ways to add advanced graphics elements to any application, but especially to
games.