Projectile emission

[Lazer]

I updated the Particle Emitter code from the book to allow for particles that have different gravities. This allows all particles that are emitted to go to the same point (think having multiple fireballs leave a spot in different directions, with different velocities and all end up at the same point). I figured I'd share the code here, and since it's pretty simple see if you think it'd be a good feature for the next Particle Designer.

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//This is added code for projectiles.
   if (isProjectileEmitter == YES) {
      aParticle->gravity = gravity;
      GLfloat gravityX = (2 * (destination.x - aParticle->position.x - ((aParticle->direction.x) * aParticle->timeToLive)) / (powf(aParticle->timeToLive, 2)));
      GLfloat gravityY = (2 * (destination.y - aParticle->position.y - ((aParticle->direction.y) * aParticle->timeToLive)) / (powf(aParticle->timeToLive, 2)));
      gravity = Vector2fMake(gravityX, gravityY);
   }
   
   aParticle->gravity = gravity;
   //End projectile code

The direction vector for a particle is it's velocity, so using the velocity, source position, and end position this calculates the necessary acceleration vector which is the gravity property. In order to update correctly, you just change updateWithDelta from:

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Vector2f tmp = Vector2fMultiply(gravity, aDelta);


To:

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Vector2f tmp = Vector2fMultiply(currentParticle->gravity, aDelta);


And add Vector2f gravity to the particle struct. Just add an init method that sets the destination and all your particles will look like they're being sucked into a black hole at that point.

[mike]

Nice update and I've put it on the list for Particle Designer 2.0

Mike