/// <summary>
/// Constructs a new particle emitter object.
/// </summary>
public ParticleEmitter(ParticleSystem particleSystem, float particlesPerSecond, Vector3 initialPosition)
{
ParticleSystem = particleSystem;
_timeBetweenParticles = 1.0f / particlesPerSecond;
ParticlesPerSecond = particlesPerSecond;
_previousPosition = initialPosition;
AllEmitters.Add(this);
}
/// <summary>
/// Updates the emitter, creating the appropriate number of particles
/// in the appropriate positions.
/// </summary>
public void Update(Vector3 newPosition, ParticleSystem particleSystem)
{
float elapsedSeconds = Engine.Instance.FrameTime;
// Work out how much time has passed since the previous update.
if (elapsedSeconds > 0 && Enabled)
{
// Work out how fast we are moving.
Vector3 velocity = (newPosition - _previousPosition) / elapsedSeconds;
// If we had any time left over that we didn't use during the
// previous update, add that to the current elapsed time.
float timeToSpend = _timeLeftOver + elapsedSeconds;
// Counter for looping over the time interval.
float currentTime = -_timeLeftOver;
// Create particles as long as we have a big enough time interval.
while (timeToSpend > _timeBetweenParticles)
{
currentTime += _timeBetweenParticles;
timeToSpend -= _timeBetweenParticles;
// Work out the optimal position for this particle. This will produce
// evenly spaced particles regardless of the object speed, particle
// creation frequency, or game update rate.
float mu = currentTime / elapsedSeconds;
Vector3 position = Vector3.Lerp(_previousPosition, newPosition, mu);
// Create the particle.
particleSystem.AddParticle(position, velocity);
}
// Store any time we didn't use, so it can be part of the next update.
_timeLeftOver = timeToSpend;
}
_previousPosition = newPosition;
}
