protected override void InitializeParticle(Particle p, Vector2 where)
            base.InitializeParticle(p, where);

            // The base works fine except for acceleration. Explosions move outwards,
            // then slow down and stop because of air resistance. Let's change
            // acceleration so that when the particle is at max lifetime, the velocity
            // will be zero.

            // We'll use the equation vt = v0 + (a0 * t). (If you're not familar with
            // this, it's one of the basic kinematics equations for constant
            // acceleration, and basically says:
            // velocity at time t = initial velocity + acceleration * t)
            // We'll solve the equation for a0, using t = p.Lifetime and vt = 0.
            p.Acceleration = -p.Velocity / p.Lifetime;
Ejemplo n.º 2
        /// <summary>
        /// InitializeParticle randomizes some properties for a particle, then
        /// calls initialize on it. It can be overriden by subclasses if they 
        /// want to modify the way particles are created. For example, 
        /// SmokePlumeParticleSystem overrides this function make all particles
        /// accelerate to the right, simulating wind.
        /// </summary>
        /// <param name="p">the particle to initialize</param>
        /// <param name="where">the position on the screen that the particle should be
        /// </param>
        protected virtual void InitializeParticle(Particle p, Vector2 where)
            // first, call PickRandomDirection to figure out which way the particle
            // will be moving. velocity and acceleration's values will come from this.
            direction = PickRandomDirection();

            // pick some random values for our particle
            float velocity =
                AeroGame.RandomBetween(minInitialSpeed, maxInitialSpeed);
            float acceleration =
                AeroGame.RandomBetween(minAcceleration, maxAcceleration);
            float lifetime =
                AeroGame.RandomBetween(minLifetime, maxLifetime);
            float scale =
                AeroGame.RandomBetween(minScale, maxScale);
            float rotationSpeed =
                AeroGame.RandomBetween(minRotationSpeed, maxRotationSpeed);

            // then initialize it with those random values. initialize will save those,
            // and make sure it is marked as active.
                where, velocity * direction, acceleration * direction,
                lifetime, scale, rotationSpeed);
Ejemplo n.º 3
        /// <summary>
        /// override the base class's Initialize to do some additional work; we want to
        /// call InitializeConstants to let subclasses set the constants that we'll use.
        /// also, the particle array and freeParticles queue are set up here.
        /// </summary>
        public void Initialize()

            // calculate the total number of particles we will ever need, using the
            // max number of effects and the max number of particles per effect.
            // once these particles are allocated, they will be reused, so that
            // we don't put any pressure on the garbage collector.
            particles = new Particle[howManyEffects * maxNumParticles];
            freeParticles = new Queue<Particle>(howManyEffects * maxNumParticles);
            for (int i = 0; i < particles.Length; i++)
                particles[i] = new Particle();