I think bullets come out now.

[rbdr/super-polarity] / Super Polarity / ParticleEngine.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace SuperPolarity
{
    class ParticleEngine
    {
        private Random random;
        public Vector2 EmitterLocation { get; set; }
        public Color Color; //TODO: Color list for random colors.
        public int TTL;
        public int TTLRandomFactor;
        public int ScatterFactor;
        public int ParticleCount;
        public float StretchFactor;
        private List<Particle> particles;
        private List<Texture2D> textures;

        public ParticleEngine(List<Texture2D> textures, Vector2 location)
        {
            EmitterLocation = location;
            this.textures = textures;
            this.particles = new List<Particle>();
            random = new Random();
            Color = Color.Red;
            TTL = 20;
            TTLRandomFactor = 40;
            StretchFactor = 1;
        }

        private Particle GenerateNewParticle()
        {
            Texture2D texture = textures[random.Next(textures.Count)];
            Vector2 position = EmitterLocation;
            Vector2 velocity = new Vector2(
                1f * (float)(random.NextDouble() * 2 - 1),
                1f * (float)(random.NextDouble() * 2 - 1));

            float angle = 0;
            float angularVelocity = 0.1f * (float)(random.NextDouble() * 2 - 1);
            Color color = Color;
            float size = (float)random.NextDouble() * StretchFactor;

            position.X += random.Next(-ScatterFactor, ScatterFactor);
            position.Y += random.Next(-ScatterFactor, ScatterFactor);

            int ttl = TTL + random.Next(TTLRandomFactor);

            return new Particle(texture, position, velocity, angle, angularVelocity, color, size, ttl);
        }

        public void Update()
        {
            int total = 10;

            for (int i = 0; i < total; i++)
            {
                particles.Add(GenerateNewParticle());
            }

            for (int particle = 0; particle < particles.Count; particle++)
            {
                particles[particle].Update();
                if (particles[particle].TTL <= 0)
                {
                    particles.RemoveAt(particle);
                    particle--;
                }
            }
        }

        public void Draw(SpriteBatch spriteBatch)
        {
            //spriteBatch.Begin();
            for (int index = 0; index < particles.Count; index++)
            {
                particles[index].Draw(spriteBatch);
            }
            //spriteBatch.End();
        }
    }
}