cocos2d starting particles from a specific time in the future

I am developing a cocos2d based app with a space background in which I am exploiting a CCQuadParticleSystem to make blinking stars. I have generated this particle system with ParticleDesigner. As soon as I load the particle system white dots representing stars start appearing in the background and after a while they fade out so that, after few seconds in which the particle system reaches the regime state, a night sky full of stars comes out.

My problem is that I would like to know if there is a way to make the particle system starting from a specific time in the future (for instance t0 = 3sec) so that I do not have to wait to have all the starts blinking.

I hope I have clearly explained the problem

thank you in advance

Andrea

Solution

I assume you are using some kind of updateWithDelta: method in your game loop in order to update the particles. If you want the particles to start after a certain interval, make your own timer.

Edit: Based on your comment below, my method is still good, it just needs some tweaking. You need only remove the condition in the updateWithDelta: method on the particle system. That way, it will still update for those 3 seconds, but will not render, and therefore look the way you are describing.

In the .h file:

BOOL particleShouldUpdate;
float particleTimer;

In your init method:

particleShouldRender = NO;
particleTimer = 3.0f;

In your updateWithDelta: method:

if(!particleShouldRender){
  particleTimer -= delta;
  if(particleTimer < 0){
    particleShouldRender = YES;
  }
}
// update your particle.

Finally, in your render method:

if(particleShouldRender){
  // render your particle.
}

Note that from this point, if you want to stop it rendering, you need only reset the 2 variables like as in the init method, and the same effect will occur.

EDIT2: Upon further clarification, we only need to adapt the init method of your particle. I will make 2 assumptions here, and you need only change them slightly to fit your needs. Suppose that your update cycle is 60 frames per second, the minimum particle lifespan is 1.01, and that you want 3 seconds of updates before you start the game. Then in the init method, try:

for(float delta = 0.0f; delta < 3.0f; delta += (1/60)){
  [particle updateWithDelta:(float)(1/60)];
}

This will update your particle like it normally would, but without rendering at each interval, and before anything else gets updated. Alternatively, if you are worried about speed when updating your particle, you can try:

for(int i = 0; i < 3; i++){
  [particle updateWithDelta:1];
  [particle updateWithDelta:0.02];
}

This will be faster, but may have a few issues depending on your particles parameters.

EDIT3: So looking into this further, cocos2D does not let you do this for some reason. I found a similar question online to this, and they suggested you play with the posVar and speed to make them large enough while you are transitioning into the scene, and once you have fully transitioned into the scene, reset the values to normal. You may want to give that a try!

Hope that Helps!