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@@ -1,368 +1,362 @@
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-#region File Description
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-//-----------------------------------------------------------------------------
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-// SmokePlumeParticleSystem.cs
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-//
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-// Microsoft XNA Community Game Platform
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-// Copyright (C) Microsoft Corporation. All rights reserved.
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-//-----------------------------------------------------------------------------
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-#endregion
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-
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-#region Using Statements
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-using System;
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-using System.Collections.Generic;
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-using System.Text;
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-using Microsoft.Xna.Framework;
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-using Microsoft.Xna.Framework.Graphics;
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-#endregion
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-
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-namespace ParticleSample
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-{
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- /// <summary>
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- /// ParticleSystem is an abstract class that provides the basic functionality to
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- /// create a particle effect. Different subclasses will have different effects,
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- /// such as fire, explosions, and plumes of smoke. To use these subclasses,
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- /// simply call AddParticles, and pass in where the particles should exist
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- /// </summary>
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- public abstract class ParticleSystem : DrawableGameComponent
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- {
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- // these two values control the order that particle systems are drawn in.
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- // typically, particles that use additive blending should be drawn on top of
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- // particles that use regular alpha blending. ParticleSystems should therefore
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- // set their DrawOrder to the appropriate value in InitializeConstants, though
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- // it is possible to use other values for more advanced effects.
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- public const int AlphaBlendDrawOrder = 100;
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- public const int AdditiveDrawOrder = 200;
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-
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- // a reference to the main game; we'll keep this around because it exposes a
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- // content manager and a sprite batch for us to use.
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- private ParticleSampleGame game;
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-
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- // the texture this particle system will use.
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- private Texture2D texture;
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-
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- // the origin when we're drawing textures. this will be the middle of the
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- // texture.
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- private Vector2 origin;
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-
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- // this number represents the maximum number of effects this particle system
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- // will be expected to draw at one time. this is set in the constructor and is
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- // used to calculate how many particles we will need.
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- private int howManyEffects;
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-
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- // the array of particles used by this system. these are reused, so that calling
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- // AddParticles will not cause any allocations.
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- Particle[] particles;
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-
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- // the queue of free particles keeps track of particles that are not curently
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- // being used by an effect. when a new effect is requested, particles are taken
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- // from this queue. when particles are finished they are put onto this queue.
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- Queue<Particle> freeParticles;
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- /// <summary>
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- /// returns the number of particles that are available for a new effect.
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- /// </summary>
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- public int FreeParticleCount
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- {
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- get { return freeParticles.Count; }
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- }
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-
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-
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- // This region of values control the "look" of the particle system, and should
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- // be set by deriving particle systems in the InitializeConstants method. The
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- // values are then used by the virtual function InitializeParticle. Subclasses
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- // can override InitializeParticle for further
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- // customization.
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- #region constants to be set by subclasses
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-
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- /// <summary>
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- /// minNumParticles and maxNumParticles control the number of particles that are
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- /// added when AddParticles is called. The number of particles will be a random
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- /// number between minNumParticles and maxNumParticles.
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- /// </summary>
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- protected int minNumParticles;
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- protected int maxNumParticles;
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-
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- /// <summary>
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- /// this controls the texture that the particle system uses. It will be used as
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- /// an argument to ContentManager.Load.
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- /// </summary>
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- protected string textureFilename;
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-
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- /// <summary>
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- /// minInitialSpeed and maxInitialSpeed are used to control the initial velocity
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- /// of the particles. The particle's initial speed will be a random number
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- /// between these two. The direction is determined by the function
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- /// PickRandomDirection, which can be overriden.
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- /// </summary>
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- protected float minInitialSpeed;
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- protected float maxInitialSpeed;
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-
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- /// <summary>
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- /// minAcceleration and maxAcceleration are used to control the acceleration of
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- /// the particles. The particle's acceleration will be a random number between
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- /// these two. By default, the direction of acceleration is the same as the
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- /// direction of the initial velocity.
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- /// </summary>
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- protected float minAcceleration;
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- protected float maxAcceleration;
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-
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- /// <summary>
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- /// minRotationSpeed and maxRotationSpeed control the particles' angular
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- /// velocity: the speed at which particles will rotate. Each particle's rotation
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- /// speed will be a random number between minRotationSpeed and maxRotationSpeed.
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- /// Use smaller numbers to make particle systems look calm and wispy, and large
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- /// numbers for more violent effects.
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- /// </summary>
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- protected float minRotationSpeed;
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- protected float maxRotationSpeed;
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-
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- /// <summary>
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- /// minLifetime and maxLifetime are used to control the lifetime. Each
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- /// particle's lifetime will be a random number between these two. Lifetime
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- /// is used to determine how long a particle "lasts." Also, in the base
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- /// implementation of Draw, lifetime is also used to calculate alpha and scale
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- /// values to avoid particles suddenly "popping" into view
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- /// </summary>
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- protected float minLifetime;
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- protected float maxLifetime;
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-
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- /// <summary>
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- /// to get some additional variance in the appearance of the particles, we give
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- /// them all random scales. the scale is a value between minScale and maxScale,
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- /// and is additionally affected by the particle's lifetime to avoid particles
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- /// "popping" into view.
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- /// </summary>
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- protected float minScale;
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- protected float maxScale;
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-
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- /// <summary>
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- /// different effects can use different blend states. fire and explosions work
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- /// well with additive blending, for example.
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- /// </summary>
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- protected BlendState blendState;
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-
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- #endregion
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-
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- /// <summary>
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- /// Constructs a new ParticleSystem.
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- /// </summary>
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- /// <param name="game">The host for this particle system. The game keeps the
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- /// content manager and sprite batch for us.</param>
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- /// <param name="howManyEffects">the maximum number of particle effects that
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- /// are expected on screen at once.</param>
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- /// <remarks>it is tempting to set the value of howManyEffects very high.
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- /// However, this value should be set to the minimum possible, because
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- /// it has a large impact on the amount of memory required, and slows down the
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- /// Update and Draw functions.</remarks>
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- protected ParticleSystem(ParticleSampleGame game, int howManyEffects)
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- : base(game)
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- {
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- this.game = game;
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- this.howManyEffects = howManyEffects;
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- }
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-
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- /// <summary>
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- /// override the base class's Initialize to do some additional work; we want to
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- /// call InitializeConstants to let subclasses set the constants that we'll use.
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- ///
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- /// also, the particle array and freeParticles queue are set up here.
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- /// </summary>
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- public override void Initialize()
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- {
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- InitializeConstants();
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-
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- // calculate the total number of particles we will ever need, using the
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- // max number of effects and the max number of particles per effect.
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- // once these particles are allocated, they will be reused, so that
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- // we don't put any pressure on the garbage collector.
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- particles = new Particle[howManyEffects * maxNumParticles];
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- freeParticles = new Queue<Particle>(howManyEffects * maxNumParticles);
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- for (int i = 0; i < particles.Length; i++)
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- {
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- particles[i] = new Particle();
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- freeParticles.Enqueue(particles[i]);
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- }
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- base.Initialize();
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- }
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-
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- /// <summary>
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- /// this abstract function must be overriden by subclasses of ParticleSystem.
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- /// It's here that they should set all the constants marked in the region
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- /// "constants to be set by subclasses", which give each ParticleSystem its
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- /// specific flavor.
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- /// </summary>
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- protected abstract void InitializeConstants();
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-
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- /// <summary>
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- /// Override the base class LoadContent to load the texture. once it's
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- /// loaded, calculate the origin.
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- /// </summary>
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- protected override void LoadContent()
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- {
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- // make sure sub classes properly set textureFilename.
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- if (string.IsNullOrEmpty(textureFilename))
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- {
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- string message = "textureFilename wasn't set properly, so the " +
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- "particle system doesn't know what texture to load. Make " +
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- "sure your particle system's InitializeConstants function " +
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- "properly sets textureFilename.";
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- throw new InvalidOperationException(message);
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- }
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- // load the texture....
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- texture = game.Content.Load<Texture2D>(textureFilename);
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-
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- // ... and calculate the center. this'll be used in the draw call, we
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- // always want to rotate and scale around this point.
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- origin.X = texture.Width / 2;
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- origin.Y = texture.Height / 2;
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-
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- base.LoadContent();
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- }
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-
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- /// <summary>
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- /// AddParticles's job is to add an effect somewhere on the screen. If there
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- /// aren't enough particles in the freeParticles queue, it will use as many as
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- /// it can. This means that if there not enough particles available, calling
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- /// AddParticles will have no effect.
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- /// </summary>
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- /// <param name="where">where the particle effect should be created</param>
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- public void AddParticles(Vector2 where)
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- {
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- // the number of particles we want for this effect is a random number
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- // somewhere between the two constants specified by the subclasses.
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- int numParticles =
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- ParticleSampleGame.Random.Next(minNumParticles, maxNumParticles);
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-
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- // create that many particles, if you can.
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- for (int i = 0; i < numParticles && freeParticles.Count > 0; i++)
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- {
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- // grab a particle from the freeParticles queue, and Initialize it.
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- Particle p = freeParticles.Dequeue();
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- InitializeParticle(p, where);
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- }
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- }
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-
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- /// <summary>
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- /// InitializeParticle randomizes some properties for a particle, then
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- /// calls initialize on it. It can be overriden by subclasses if they
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- /// want to modify the way particles are created. For example,
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- /// SmokePlumeParticleSystem overrides this function make all particles
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- /// accelerate to the right, simulating wind.
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- /// </summary>
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- /// <param name="p">the particle to initialize</param>
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- /// <param name="where">the position on the screen that the particle should be
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- /// </param>
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- protected virtual void InitializeParticle(Particle p, Vector2 where)
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- {
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- // first, call PickRandomDirection to figure out which way the particle
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- // will be moving. velocity and acceleration's values will come from this.
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- Vector2 direction = PickRandomDirection();
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-
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- // pick some random values for our particle
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- float velocity =
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- ParticleSampleGame.RandomBetween(minInitialSpeed, maxInitialSpeed);
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- float acceleration =
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- ParticleSampleGame.RandomBetween(minAcceleration, maxAcceleration);
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- float lifetime =
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- ParticleSampleGame.RandomBetween(minLifetime, maxLifetime);
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- float scale =
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- ParticleSampleGame.RandomBetween(minScale, maxScale);
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- float rotationSpeed =
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- ParticleSampleGame.RandomBetween(minRotationSpeed, maxRotationSpeed);
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-
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- // then initialize it with those random values. initialize will save those,
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- // and make sure it is marked as active.
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- p.Initialize(
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- where, velocity * direction, acceleration * direction,
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- lifetime, scale, rotationSpeed);
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- }
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-
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- /// <summary>
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- /// PickRandomDirection is used by InitializeParticles to decide which direction
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- /// particles will move. The default implementation is a random vector in a
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- /// circular pattern.
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- /// </summary>
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- protected virtual Vector2 PickRandomDirection()
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- {
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- float angle = ParticleSampleGame.RandomBetween(0, MathHelper.TwoPi);
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- return new Vector2((float)Math.Cos(angle), (float)Math.Sin(angle));
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- }
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-
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- /// <summary>
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- /// overriden from DrawableGameComponent, Update will update all of the active
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- /// particles.
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- /// </summary>
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- public override void Update(GameTime gameTime)
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- {
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- // calculate dt, the change in the since the last frame. the particle
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- // updates will use this value.
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- float dt = (float)gameTime.ElapsedGameTime.TotalSeconds;
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-
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- // go through all of the particles...
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- foreach (Particle p in particles)
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- {
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-
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- if (p.Active)
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- {
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- // ... and if they're active, update them.
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- p.Update(dt);
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- // if that update finishes them, put them onto the free particles
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- // queue.
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- if (!p.Active)
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- {
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- freeParticles.Enqueue(p);
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- }
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- }
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- }
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-
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- base.Update(gameTime);
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- }
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-
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- /// <summary>
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- /// overriden from DrawableGameComponent, Draw will use ParticleSampleGame's
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- /// sprite batch to render all of the active particles.
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- /// </summary>
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- public override void Draw(GameTime gameTime)
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- {
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- // tell sprite batch to begin, using the spriteBlendMode specified in
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- // initializeConstants
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- game.SpriteBatch.Begin(SpriteSortMode.Deferred, blendState);
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-
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- foreach (Particle p in particles)
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- {
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- // skip inactive particles
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- if (!p.Active)
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- continue;
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-
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- // normalized lifetime is a value from 0 to 1 and represents how far
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- // a particle is through its life. 0 means it just started, .5 is half
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- // way through, and 1.0 means it's just about to be finished.
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- // this value will be used to calculate alpha and scale, to avoid
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- // having particles suddenly appear or disappear.
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- float normalizedLifetime = p.TimeSinceStart / p.Lifetime;
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-
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- // we want particles to fade in and fade out, so we'll calculate alpha
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- // to be (normalizedLifetime) * (1-normalizedLifetime). this way, when
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- // normalizedLifetime is 0 or 1, alpha is 0. the maximum value is at
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- // normalizedLifetime = .5, and is
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- // (normalizedLifetime) * (1-normalizedLifetime)
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- // (.5) * (1-.5)
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- // .25
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- // since we want the maximum alpha to be 1, not .25, we'll scale the
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- // entire equation by 4.
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- float alpha = 4 * normalizedLifetime * (1 - normalizedLifetime);
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- Color color = Color.White * alpha;
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-
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- // make particles grow as they age. they'll start at 75% of their size,
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- // and increase to 100% once they're finished.
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- float scale = p.Scale * (.75f + .25f * normalizedLifetime);
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-
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- game.SpriteBatch.Draw(texture, p.Position, null, color,
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- p.Rotation, origin, scale, SpriteEffects.None, 0.0f);
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- }
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-
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- game.SpriteBatch.End();
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-
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- base.Draw(gameTime);
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- }
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- }
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-}
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+//-----------------------------------------------------------------------------
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+// SmokePlumeParticleSystem.cs
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+//
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+// Microsoft XNA Community Game Platform
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+// Copyright (C) Microsoft Corporation. All rights reserved.
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+//-----------------------------------------------------------------------------
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+
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+using System;
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+using System.Collections.Generic;
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+using System.Text;
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+using Microsoft.Xna.Framework;
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+using Microsoft.Xna.Framework.Graphics;
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+
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+namespace ParticleSample
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+{
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+ /// <summary>
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+ /// ParticleSystem is an abstract class that provides the basic functionality to
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+ /// create a particle effect. Different subclasses will have different effects,
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+ /// such as fire, explosions, and plumes of smoke. To use these subclasses,
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+ /// simply call AddParticles, and pass in where the particles should exist
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+ /// </summary>
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+ public abstract class ParticleSystem : DrawableGameComponent
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+ {
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+ // these two values control the order that particle systems are drawn in.
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+ // typically, particles that use additive blending should be drawn on top of
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+ // particles that use regular alpha blending. ParticleSystems should therefore
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+ // set their DrawOrder to the appropriate value in InitializeConstants, though
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+ // it is possible to use other values for more advanced effects.
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+ public const int AlphaBlendDrawOrder = 100;
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+ public const int AdditiveDrawOrder = 200;
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+
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+ // a reference to the main game; we'll keep this around because it exposes a
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+ // content manager and a sprite batch for us to use.
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+ private ParticleSampleGame game;
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+
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+ // the texture this particle system will use.
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+ private Texture2D texture;
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+
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+ // the origin when we're drawing textures. this will be the middle of the
|
|
|
+ // texture.
|
|
|
+ private Vector2 origin;
|
|
|
+
|
|
|
+ // this number represents the maximum number of effects this particle system
|
|
|
+ // will be expected to draw at one time. this is set in the constructor and is
|
|
|
+ // used to calculate how many particles we will need.
|
|
|
+ private int howManyEffects;
|
|
|
+
|
|
|
+ // the array of particles used by this system. these are reused, so that calling
|
|
|
+ // AddParticles will not cause any allocations.
|
|
|
+ Particle[] particles;
|
|
|
+
|
|
|
+ // the queue of free particles keeps track of particles that are not curently
|
|
|
+ // being used by an effect. when a new effect is requested, particles are taken
|
|
|
+ // from this queue. when particles are finished they are put onto this queue.
|
|
|
+ Queue<Particle> freeParticles;
|
|
|
+ /// <summary>
|
|
|
+ /// returns the number of particles that are available for a new effect.
|
|
|
+ /// </summary>
|
|
|
+ public int FreeParticleCount
|
|
|
+ {
|
|
|
+ get { return freeParticles.Count; }
|
|
|
+ }
|
|
|
+
|
|
|
+
|
|
|
+ // This region of values control the "look" of the particle system, and should
|
|
|
+ // be set by deriving particle systems in the InitializeConstants method. The
|
|
|
+ // values are then used by the virtual function InitializeParticle. Subclasses
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|
|
+ // can override InitializeParticle for further
|
|
|
+ // customization.
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// minNumParticles and maxNumParticles control the number of particles that are
|
|
|
+ /// added when AddParticles is called. The number of particles will be a random
|
|
|
+ /// number between minNumParticles and maxNumParticles.
|
|
|
+ /// </summary>
|
|
|
+ protected int minNumParticles;
|
|
|
+ protected int maxNumParticles;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// this controls the texture that the particle system uses. It will be used as
|
|
|
+ /// an argument to ContentManager.Load.
|
|
|
+ /// </summary>
|
|
|
+ protected string textureFilename;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// minInitialSpeed and maxInitialSpeed are used to control the initial velocity
|
|
|
+ /// of the particles. The particle's initial speed will be a random number
|
|
|
+ /// between these two. The direction is determined by the function
|
|
|
+ /// PickRandomDirection, which can be overriden.
|
|
|
+ /// </summary>
|
|
|
+ protected float minInitialSpeed;
|
|
|
+ protected float maxInitialSpeed;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// minAcceleration and maxAcceleration are used to control the acceleration of
|
|
|
+ /// the particles. The particle's acceleration will be a random number between
|
|
|
+ /// these two. By default, the direction of acceleration is the same as the
|
|
|
+ /// direction of the initial velocity.
|
|
|
+ /// </summary>
|
|
|
+ protected float minAcceleration;
|
|
|
+ protected float maxAcceleration;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// minRotationSpeed and maxRotationSpeed control the particles' angular
|
|
|
+ /// velocity: the speed at which particles will rotate. Each particle's rotation
|
|
|
+ /// speed will be a random number between minRotationSpeed and maxRotationSpeed.
|
|
|
+ /// Use smaller numbers to make particle systems look calm and wispy, and large
|
|
|
+ /// numbers for more violent effects.
|
|
|
+ /// </summary>
|
|
|
+ protected float minRotationSpeed;
|
|
|
+ protected float maxRotationSpeed;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// minLifetime and maxLifetime are used to control the lifetime. Each
|
|
|
+ /// particle's lifetime will be a random number between these two. Lifetime
|
|
|
+ /// is used to determine how long a particle "lasts." Also, in the base
|
|
|
+ /// implementation of Draw, lifetime is also used to calculate alpha and scale
|
|
|
+ /// values to avoid particles suddenly "popping" into view
|
|
|
+ /// </summary>
|
|
|
+ protected float minLifetime;
|
|
|
+ protected float maxLifetime;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// to get some additional variance in the appearance of the particles, we give
|
|
|
+ /// them all random scales. the scale is a value between minScale and maxScale,
|
|
|
+ /// and is additionally affected by the particle's lifetime to avoid particles
|
|
|
+ /// "popping" into view.
|
|
|
+ /// </summary>
|
|
|
+ protected float minScale;
|
|
|
+ protected float maxScale;
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// different effects can use different blend states. fire and explosions work
|
|
|
+ /// well with additive blending, for example.
|
|
|
+ /// </summary>
|
|
|
+ protected BlendState blendState;
|
|
|
+
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// Constructs a new ParticleSystem.
|
|
|
+ /// </summary>
|
|
|
+ /// <param name="game">The host for this particle system. The game keeps the
|
|
|
+ /// content manager and sprite batch for us.</param>
|
|
|
+ /// <param name="howManyEffects">the maximum number of particle effects that
|
|
|
+ /// are expected on screen at once.</param>
|
|
|
+ /// <remarks>it is tempting to set the value of howManyEffects very high.
|
|
|
+ /// However, this value should be set to the minimum possible, because
|
|
|
+ /// it has a large impact on the amount of memory required, and slows down the
|
|
|
+ /// Update and Draw functions.</remarks>
|
|
|
+ protected ParticleSystem(ParticleSampleGame game, int howManyEffects)
|
|
|
+ : base(game)
|
|
|
+ {
|
|
|
+ this.game = game;
|
|
|
+ this.howManyEffects = howManyEffects;
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// override the base class's Initialize to do some additional work; we want to
|
|
|
+ /// call InitializeConstants to let subclasses set the constants that we'll use.
|
|
|
+ ///
|
|
|
+ /// also, the particle array and freeParticles queue are set up here.
|
|
|
+ /// </summary>
|
|
|
+ public override void Initialize()
|
|
|
+ {
|
|
|
+ InitializeConstants();
|
|
|
+
|
|
|
+ // calculate the total number of particles we will ever need, using the
|
|
|
+ // max number of effects and the max number of particles per effect.
|
|
|
+ // once these particles are allocated, they will be reused, so that
|
|
|
+ // we don't put any pressure on the garbage collector.
|
|
|
+ particles = new Particle[howManyEffects * maxNumParticles];
|
|
|
+ freeParticles = new Queue<Particle>(howManyEffects * maxNumParticles);
|
|
|
+ for (int i = 0; i < particles.Length; i++)
|
|
|
+ {
|
|
|
+ particles[i] = new Particle();
|
|
|
+ freeParticles.Enqueue(particles[i]);
|
|
|
+ }
|
|
|
+ base.Initialize();
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// this abstract function must be overriden by subclasses of ParticleSystem.
|
|
|
+ /// It's here that they should set all the constants marked in the region
|
|
|
+ /// "constants to be set by subclasses", which give each ParticleSystem its
|
|
|
+ /// specific flavor.
|
|
|
+ /// </summary>
|
|
|
+ protected abstract void InitializeConstants();
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// Override the base class LoadContent to load the texture. once it's
|
|
|
+ /// loaded, calculate the origin.
|
|
|
+ /// </summary>
|
|
|
+ protected override void LoadContent()
|
|
|
+ {
|
|
|
+ // make sure sub classes properly set textureFilename.
|
|
|
+ if (string.IsNullOrEmpty(textureFilename))
|
|
|
+ {
|
|
|
+ string message = "textureFilename wasn't set properly, so the " +
|
|
|
+ "particle system doesn't know what texture to load. Make " +
|
|
|
+ "sure your particle system's InitializeConstants function " +
|
|
|
+ "properly sets textureFilename.";
|
|
|
+ throw new InvalidOperationException(message);
|
|
|
+ }
|
|
|
+ // load the texture....
|
|
|
+ texture = game.Content.Load<Texture2D>(textureFilename);
|
|
|
+
|
|
|
+ // ... and calculate the center. this'll be used in the draw call, we
|
|
|
+ // always want to rotate and scale around this point.
|
|
|
+ origin.X = texture.Width / 2;
|
|
|
+ origin.Y = texture.Height / 2;
|
|
|
+
|
|
|
+ base.LoadContent();
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// AddParticles's job is to add an effect somewhere on the screen. If there
|
|
|
+ /// aren't enough particles in the freeParticles queue, it will use as many as
|
|
|
+ /// it can. This means that if there not enough particles available, calling
|
|
|
+ /// AddParticles will have no effect.
|
|
|
+ /// </summary>
|
|
|
+ /// <param name="where">where the particle effect should be created</param>
|
|
|
+ public void AddParticles(Vector2 where)
|
|
|
+ {
|
|
|
+ // the number of particles we want for this effect is a random number
|
|
|
+ // somewhere between the two constants specified by the subclasses.
|
|
|
+ int numParticles =
|
|
|
+ ParticleSampleGame.Random.Next(minNumParticles, maxNumParticles);
|
|
|
+
|
|
|
+ // create that many particles, if you can.
|
|
|
+ for (int i = 0; i < numParticles && freeParticles.Count > 0; i++)
|
|
|
+ {
|
|
|
+ // grab a particle from the freeParticles queue, and Initialize it.
|
|
|
+ Particle p = freeParticles.Dequeue();
|
|
|
+ InitializeParticle(p, where);
|
|
|
+ }
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// InitializeParticle randomizes some properties for a particle, then
|
|
|
+ /// calls initialize on it. It can be overriden by subclasses if they
|
|
|
+ /// want to modify the way particles are created. For example,
|
|
|
+ /// SmokePlumeParticleSystem overrides this function make all particles
|
|
|
+ /// accelerate to the right, simulating wind.
|
|
|
+ /// </summary>
|
|
|
+ /// <param name="p">the particle to initialize</param>
|
|
|
+ /// <param name="where">the position on the screen that the particle should be
|
|
|
+ /// </param>
|
|
|
+ protected virtual void InitializeParticle(Particle p, Vector2 where)
|
|
|
+ {
|
|
|
+ // first, call PickRandomDirection to figure out which way the particle
|
|
|
+ // will be moving. velocity and acceleration's values will come from this.
|
|
|
+ Vector2 direction = PickRandomDirection();
|
|
|
+
|
|
|
+ // pick some random values for our particle
|
|
|
+ float velocity =
|
|
|
+ ParticleSampleGame.RandomBetween(minInitialSpeed, maxInitialSpeed);
|
|
|
+ float acceleration =
|
|
|
+ ParticleSampleGame.RandomBetween(minAcceleration, maxAcceleration);
|
|
|
+ float lifetime =
|
|
|
+ ParticleSampleGame.RandomBetween(minLifetime, maxLifetime);
|
|
|
+ float scale =
|
|
|
+ ParticleSampleGame.RandomBetween(minScale, maxScale);
|
|
|
+ float rotationSpeed =
|
|
|
+ ParticleSampleGame.RandomBetween(minRotationSpeed, maxRotationSpeed);
|
|
|
+
|
|
|
+ // then initialize it with those random values. initialize will save those,
|
|
|
+ // and make sure it is marked as active.
|
|
|
+ p.Initialize(
|
|
|
+ where, velocity * direction, acceleration * direction,
|
|
|
+ lifetime, scale, rotationSpeed);
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// PickRandomDirection is used by InitializeParticles to decide which direction
|
|
|
+ /// particles will move. The default implementation is a random vector in a
|
|
|
+ /// circular pattern.
|
|
|
+ /// </summary>
|
|
|
+ protected virtual Vector2 PickRandomDirection()
|
|
|
+ {
|
|
|
+ float angle = ParticleSampleGame.RandomBetween(0, MathHelper.TwoPi);
|
|
|
+ return new Vector2((float)Math.Cos(angle), (float)Math.Sin(angle));
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// overriden from DrawableGameComponent, Update will update all of the active
|
|
|
+ /// particles.
|
|
|
+ /// </summary>
|
|
|
+ public override void Update(GameTime gameTime)
|
|
|
+ {
|
|
|
+ // calculate dt, the change in the since the last frame. the particle
|
|
|
+ // updates will use this value.
|
|
|
+ float dt = (float)gameTime.ElapsedGameTime.TotalSeconds;
|
|
|
+
|
|
|
+ // go through all of the particles...
|
|
|
+ foreach (Particle p in particles)
|
|
|
+ {
|
|
|
+
|
|
|
+ if (p.Active)
|
|
|
+ {
|
|
|
+ // ... and if they're active, update them.
|
|
|
+ p.Update(dt);
|
|
|
+ // if that update finishes them, put them onto the free particles
|
|
|
+ // queue.
|
|
|
+ if (!p.Active)
|
|
|
+ {
|
|
|
+ freeParticles.Enqueue(p);
|
|
|
+ }
|
|
|
+ }
|
|
|
+ }
|
|
|
+
|
|
|
+ base.Update(gameTime);
|
|
|
+ }
|
|
|
+
|
|
|
+ /// <summary>
|
|
|
+ /// overriden from DrawableGameComponent, Draw will use ParticleSampleGame's
|
|
|
+ /// sprite batch to render all of the active particles.
|
|
|
+ /// </summary>
|
|
|
+ public override void Draw(GameTime gameTime)
|
|
|
+ {
|
|
|
+ // tell sprite batch to begin, using the spriteBlendMode specified in
|
|
|
+ // initializeConstants
|
|
|
+ game.SpriteBatch.Begin(SpriteSortMode.Deferred, blendState);
|
|
|
+
|
|
|
+ foreach (Particle p in particles)
|
|
|
+ {
|
|
|
+ // skip inactive particles
|
|
|
+ if (!p.Active)
|
|
|
+ continue;
|
|
|
+
|
|
|
+ // normalized lifetime is a value from 0 to 1 and represents how far
|
|
|
+ // a particle is through its life. 0 means it just started, .5 is half
|
|
|
+ // way through, and 1.0 means it's just about to be finished.
|
|
|
+ // this value will be used to calculate alpha and scale, to avoid
|
|
|
+ // having particles suddenly appear or disappear.
|
|
|
+ float normalizedLifetime = p.TimeSinceStart / p.Lifetime;
|
|
|
+
|
|
|
+ // we want particles to fade in and fade out, so we'll calculate alpha
|
|
|
+ // to be (normalizedLifetime) * (1-normalizedLifetime). this way, when
|
|
|
+ // normalizedLifetime is 0 or 1, alpha is 0. the maximum value is at
|
|
|
+ // normalizedLifetime = .5, and is
|
|
|
+ // (normalizedLifetime) * (1-normalizedLifetime)
|
|
|
+ // (.5) * (1-.5)
|
|
|
+ // .25
|
|
|
+ // since we want the maximum alpha to be 1, not .25, we'll scale the
|
|
|
+ // entire equation by 4.
|
|
|
+ float alpha = 4 * normalizedLifetime * (1 - normalizedLifetime);
|
|
|
+ Color color = Color.White * alpha;
|
|
|
+
|
|
|
+ // make particles grow as they age. they'll start at 75% of their size,
|
|
|
+ // and increase to 100% once they're finished.
|
|
|
+ float scale = p.Scale * (.75f + .25f * normalizedLifetime);
|
|
|
+
|
|
|
+ game.SpriteBatch.Draw(texture, p.Position, null, color,
|
|
|
+ p.Rotation, origin, scale, SpriteEffects.None, 0.0f);
|
|
|
+ }
|
|
|
+
|
|
|
+ game.SpriteBatch.End();
|
|
|
+
|
|
|
+ base.Draw(gameTime);
|
|
|
+ }
|
|
|
+ }
|
|
|
+}
|
CartBlanche
