Oyyou.MonoGameTutorials/MonoGame_Tutorials/Tutorial024/Emitters/Emitter.cs

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tutorial024.Sprites;

namespace Tutorial024.Emitters
{
  public abstract class Emitter : Component
  {
    private float _generateTimer;

    private float _swayTimer;

    protected Sprite _particlePrefab;

    protected List<Sprite> _particles;

    /// <summary>
    /// How often a particle is produced
    /// </summary>
    public float GenerateSpeed = 0.005f;

    /// <summary>
    /// How often we apply the "GlobalVelociy" to our particles
    /// </summary>
    public float GlobalVelocitySpeed = 1;

    public int MaxParticles = 1000;

    public Emitter(Sprite particle)
    {
      _particlePrefab = particle;

      _particles = new List<Sprite>();
    }

    public override void Update(GameTime gameTime)
    {
      _generateTimer += (float)gameTime.ElapsedGameTime.TotalSeconds;
      _swayTimer += (float)gameTime.ElapsedGameTime.TotalSeconds;

      AddParticle();

      if (_swayTimer > GlobalVelocitySpeed)
      {
        _swayTimer = 0;

        ApplyGlobalVelocity();
      }

      foreach (var particle in _particles)
        particle.Update(gameTime);

      RemovedFinishedParticles();
    }

    private void AddParticle()
    {
      if (_generateTimer > GenerateSpeed)
      {
        _generateTimer = 0;

        if (_particles.Count < MaxParticles)
        {
          _particles.Add(GenerateParticle());
        }
      }
    }

    protected abstract void ApplyGlobalVelocity();

    private void RemovedFinishedParticles()
    {
      for (int i = 0; i < _particles.Count; i++)
      {
        if (_particles[i].IsRemoved)
        {
          _particles.RemoveAt(i);
          i--;
        }
      }
    }

    protected abstract Sprite GenerateParticle();

    public override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
    {
      foreach (var particle in _particles)
        particle.Draw(gameTime, spriteBatch);
    }
  }
}