Question

I am interested in developing a particle engine which I can call something like .createCollisionEffect(pos x, pos y, float duration);

And the engine will create a random-directional spur of particles for the specified duration. I found the following code but I would like to use 3 different textures so it randomly chooses one, However I am not sure how to manage the time and the 3 different textures: I found the following code:

    public ParticleSystem createParticleSystem(final TextureRegion textureRegion) {
    //X & Y for the particles to spawn at.
    final float particlesXSpawn = 400;
    final float particlesYSpawn = 300;

    //Max & min rate are the maximum particles per second and the minimum particles per second.
    final float maxRate = 10;
    final float minRate = 5;

    //This variable determines the maximum particles in the particle system.
    final int maxParticles = 100;

    //Particle emitter which will set all of the particles at a ertain point when they are initialized.
    final PointParticleEmitter pointParticleEmtitter = new PointParticleEmitter(particlesXSpawn, particlesYSpawn);

    //Creating the particle system.
    final ParticleSystem particleSystem = new ParticleSystem(pointParticleEmtitter, maxRate, minRate, maxParticles, textureRegion);

    //And now, lets create the initiallizers and modifiers.
    //Velocity initiallizer - will pick a random velocity from -20 to 20 on the x & y axes. Play around with this value.
    particleSystem.addParticleInitializer(new VelocityInitializer(-20, 20, -20, 20));

    //Acceleration initializer - gives all the particles the earth gravity (so they accelerate down).
    particleSystem.addParticleInitializer(new GravityInitializer());

    //And now, adding an alpha modifier, so particles slowly fade out. This makes a particle go from alpha = 1 to alpha = 0 in 3 seconds, starting exactly when the particle is spawned.
    particleSystem.addParticleModifier((IParticleModifier) new AlphaModifier(3, 1, 0));

    //Lastly, expire modifier. Make particles die after 3 seconds - their alpha reached 0.
    particleSystem.addParticleModifier(new ExpireModifier(3));  

    return particleSystem;
}

Can anyone provide some guidance ? Thanks in advance!

Answer 1

You have the basics in your code above. Here is how to do what you are looking for:

1. create a particleEmitter
2. Create a particle system
3. Add Modifiers and initializers to give your particles the behavior you want.

And now the secret sauce:

1. Stop your particle system: particleSystem.setParticlesSpawnEnabled(false);

2. On a collision, move your particle emitter where it should emit particles using: particleEmitter.setCenter(xPosition , yPosition);

3. Start a TimerHandler to shut off the particles when the time for spawning particles is over. TimerHandler is an Andengine class that works like a handler, but pauses and resumes with the game.

That should do ya!