// InitializeParticle is overridden to add the appearance of wind.
protected override void InitializeParticle(Particle particle, Vector2 where)
{
base.InitializeParticle(particle, where);
// The base is mostly good, but we want to simulate a little bit of wind heading to the right.
particle.Acceleration.X += Utils.RandomBetween(10, 50);
}
protected override void InitializeParticle(Particle particle, Vector2 where)
{
base.InitializeParticle(particle, 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 = particle.Lifetime and vt = 0.
particle.Acceleration = -particle.Velocity / particle.Lifetime;
}
// Randomizes some properties for a particle, then calls Initialize on it.
// This 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.
protected virtual void InitializeParticle(Particle particle, Vector2 where)
{
// First, call PickRandomDirection to figure out which way the particle
// will be moving. Velocity and acceleration values will come from this.
Vector2 direction = PickRandomDirection();
// Pick some random values for our particle.
float velocity = Utils.RandomBetween(minInitialSpeed, maxInitialSpeed);
float acceleration = Utils.RandomBetween(minAcceleration, maxAcceleration);
float lifetime = Utils.RandomBetween(minLifetime, maxLifetime);
float scale = Utils.RandomBetween(minScale, maxScale);
float rotationSpeed = Utils.RandomBetween(minRotationSpeed, maxRotationSpeed);
// Then initialize the particle with these random values.
particle.Initialize(where, velocity * direction, acceleration * direction, lifetime, scale, rotationSpeed);
}