source: 2010/23/sijoseha/alpha/Effects/ParticleGame.cs @ 822

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;
using Microsoft.Xna.Framework.Net;
using Microsoft.Xna.Framework.Storage;

namespace Effects
{
    /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class ParticleGame : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        public SpriteBatch SpriteBatch
        {
            get { return spriteBatch; }
        }
        
        
        Particle[] particles;
        Random random = new Random();
        const int amountOfParticles = 15;

        KeyboardState previousKeyboardState = Keyboard.GetState();

        public ParticleGame()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";
        }

        /// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here

            base.Initialize();
        }

        /// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        {
            particles = new Particle[amountOfParticles];
            Texture2D glowTexture = Content.Load<Texture2D>("Glow");
            Texture2D glowTexture2 = Content.Load<Texture2D>("Glow2");
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);
            for (int i = 0; i < particles.Length; i++)
            {
                particles[i] = new Particle(this, glowTexture, glowTexture2, new Vector2(
                    (float)random.NextDouble() * graphics.GraphicsDevice.Viewport.Width,
                    (float)random.NextDouble() * graphics.GraphicsDevice.Viewport.Height), 2.0f);
                particles[i].Scale = (float)random.NextDouble();//0.2f + (float)random.NextDouble() * 0.8f;
                particles[i].Velocity = new Vector2(
                    (float)random.NextDouble() * 5 - 2.5f,
                    (float)random.NextDouble() * 5 - 2.5f);

            }
            // TODO: use this.Content to load your game content here
        }

        /// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// all content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

        /// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Update(GameTime gameTime)
        {
            float dt = (float)gameTime.ElapsedGameTime.TotalSeconds;
            KeyboardState keyboardState = Keyboard.GetState();
            MouseState mouseState = Mouse.GetState();
            // Allows the game to exit
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();
            for (int i = 0; i < particles.Length; i++)
            {
                if (particles[i].Alive)
                {
                    particles[i].CurrentTime += dt;
                    particles[i].Scale = 1.0f - (particles[i].Lifetime * particles[i].CurrentTime);
                    particles[i].Position += particles[i].Velocity;
                    if (particles[i].CurrentTime > particles[i].Lifetime)
                    {
                        particles[i].Alive = false;
                    }
                }
                if (!particles[i].Alive)
                {
                    particles[i].Alive = true;
                    particles[i].Lifetime = 2.0f;
                    particles[i].CurrentTime = 0.0f;
                    particles[i].Scale = 1.0f;
                    particles[i].Position = new Vector2(
                        (float)mouseState.X,
                        (float)mouseState.Y);
                    particles[i].Velocity = new Vector2(
                        (float)random.NextDouble() * 5 - 2.5f,
                        (float)random.NextDouble() * 5 - 2.5f);
                    //particles[i].Position = new Vector2(
                    //(float)random.NextDouble() * graphics.GraphicsDevice.Viewport.Width,
                    //(float)random.NextDouble() * graphics.GraphicsDevice.Viewport.Height);
                }
            }

            // TODO: Add your update logic here

            previousKeyboardState = keyboardState;
            base.Update(gameTime);
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.Black);
            // TODO: Add your drawing code here

            base.Draw(gameTime);
        }
    }
}