ジェットストリーム

■残像？
　残像って？と聞かれたので、何種類か実験で作成してみました、このサンプルは、1つのパーティクルに対して「particleCount 」で指定した分残像の座標を保持して残像部分を表現する方法です。
■ソース
Game1.cs

namespace WindowsGame
{
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        ContentManager content;
        SpriteBatch sprite;
        Texture2D texture;
        const int particleCount = 20;
        Particle particle;
        
        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            content = new ContentManager(Services);
        }

        protected override void Initialize()
        {
            Random ran = new Random();
                particle = new Particle(
                    (float)ran.Next(700),
                    (float)ran.Next(500),
                    (float)ran.Next(360) * 3.14159f / 180.0f,
                    particleCount);
            base.Initialize();
        }

        protected override void LoadGraphicsContent(bool loadAllContent)
        {
            if (loadAllContent)
            {
                sprite = new SpriteBatch(graphics.GraphicsDevice);
                texture = content.Load<Texture2D>("ball");
            }
        }

        protected override void Update(GameTime gameTime)
        {
            particle.Move();
            base.Update(gameTime);
        }

        protected override void Draw(GameTime gameTime)
        {
            graphics.GraphicsDevice.Clear(Color.Black);
            sprite.Begin(SpriteBlendMode.Additive);

            byte c;
            for (int i = 0; i < particleCount; i++)
            {
                c = (byte)(255 / (i + 1));
                sprite.Draw(texture, particle.Pos[i], new Color(c, c, c, 255));
            }
            sprite.End();
            base.Draw(gameTime);
        }
    }
}

Particle.cs

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

namespace WindowsGame
{
    class Particle
    {
        public int countMax;
        public Vector2[] Pos;
        public Vector2 Direction;

        public Particle(float x, float y, float ang, int count)
        {
            countMax    = count;
            Pos = new Vector2[ countMax];
            Pos[ 0 ] = new Vector2(x, y);
            Direction = new Vector2((float)Math.Sin(ang) * 10.0f, (float)Math.Cos(ang) * 10.0f);
            //同じ座標にコピー
            for (int i = 1; i < countMax; i++)
                Pos[i] = Pos[i - 1];
        }

        public void Move()
        {
            Pos[ 0 ] += Direction;
            if ((Pos[ 0 ].X < 0) || (Pos[ 0 ].X > 800 - 64))
                Direction.X = -Direction.X;
            if ((Pos[ 0 ].Y < 0) || (Pos[ 0 ].Y > 600 - 64))
                Direction.Y = -Direction.Y;
            //座標をずらそう
            for (int i = countMax-1; i > 0; i--)
                Pos[ i ] = Pos[ i - 1 ];
        }
    }

}

■結果