ParticleManager.cs

public static class ParticleManager
{
    const int InitialPoolCapacity = 32;

    public static ulong EndIndex = 0;

    public static Particle[] Particles = new Particle[InitialPoolCapacity * 64];

    public static int CreateParticle(string texture, float x = 0, float y = 0, float deltaRotation = 0, float velocity = 0, float scale = 1, float depth = 1, float transparency = 0, float rotation = 0)
    {
        Particle particle = new Particle
        {
            X = x,
            Y = y,
            Texture = texture,
            DeltaRotation = deltaRotation,
            Velocity = velocity,
            Scale = scale,
            Depth = depth,
            Transparency = transparency,
            Rotation = rotation,
        };

        Particles[EndIndex] = particle;
        EndIndex++;

        if (EndIndex >= (ulong)Particles.Length)
            ExpandParticleSet();

        return (int)EndIndex - 1;
    }

    public static void ExpandParticleSet()
    {
        Particle[] newParticles = new Particle[Particles.Length * 2];
        Particles.CopyTo(newParticles, 0);
        Particles = newParticles;
    }

    public static void FreeParticle(ulong id)
    {
        Particles[id] = Particles[EndIndex-1];
        EndIndex--;
    }
}

public struct Particle
{
    public float X;
    public float Y;
    public string Texture;
    public float DeltaRotation;
    public float Velocity;
    public float Scale;
    public float Depth;
    public float Transparency;
    public float Rotation;
}