Particle Systems

Asst. Prof. Rujchai Ung-arunyawee

COE, KKU

Laws of Motion

Position Velocity Acceleration Mass Force Newton’s Laws

Velocity Differential

dpv p

dt

Integral

p p pt

Code

Position += Velocity*time;

Acceleration Differential 2

2

d pa p

dt

Integral

21

2

p p pt

p p pt pt

Code

Position += Velocity*time +

acceleration*time*time* 0.5;

OR

Position += Velocity*time;

Force Equation

1

f ma mp

p fm

Code

acceleration = inversemass*force;

Integrator for Particle Update public void Integrate(float duration) { // Update linear position position.X += velocity.X * duration; position.Y += velocity.Y * duration; position.Z += velocity.Z * duration;

// Update linear velocity Vector3 resultingAcc = acceleration; resultingAcc.X += forceAccum.X * inverseMass; resultingAcc.Y += forceAccum.Y * inverseMass; resultingAcc.Z += forceAccum.Z * inverseMass; velocity.X += resultingAcc.X * duration; velocity.Y += resultingAcc.Y * duration; velocity.Z += resultingAcc.Z * duration;

// Impose drag. float scale = (float)Math.Pow(damping, duration); velocity = Vector3.Multiply(velocity, scale); }

Particle ClassParticleClass

Fields

accelerationdampingforceAccuminverseMasspositionvelocity

Properties

AccelerationDampingMassPositionVelocity

Methods

addForceclearAccumulatorIntegrateParticle

Game Class

Game Update()protected override void Update(GameTime gameTime){ // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back

== ButtonState.Pressed) this.Exit();

// TODO: Add your update logic here KeyboardState kb = Keyboard.GetState(); MouseState mouse = Mouse.GetState(); if (mouse.LeftButton == ButtonState.Pressed) fire(gameTime); float duration = gameTime.ElapsedGameTime.Milliseconds

/ (1000.0f); ammos.Integrate(duration); base.Update(gameTime);}

Fire() Method

private void fire(GameTime gametime){ // Artillery ammos.Mass = 200.0f; // 200.0kg ammos.Velocity = new Vector3(0.0f, 30.0f, 40.0f);// 50m/s ammos.Acceleration = new Vector3(0.0f, -20.0f, 0.0f); ammos.Damping = 0.99f; ammos.Position = new Vector3(0.0f, 1.5f, 0.0f); ammos.clearAccumulator();}

Draw the particle foreach (ModelMesh mesh in myModel.Meshes) { // Draw the current mesh foreach (BasicEffect eff in mesh.Effects) { eff.World = Matrix.CreateScale(0.03f); eff.World *=

Matrix.CreateTranslation(ammos.Position); eff.View = effect.View; eff.Projection = effect.Projection; eff.EnableDefaultLighting(); } mesh.Draw(); }

Camera Settings

// Set the Viewing Matrixeffect.View =

Matrix.CreateLookAt(new Vector3(-25.0f, 8.0f, -5.0f), new Vector3(0.0f, 5.0f, 22.0f), Vector3.Up);

// Set the Projection Matrixeffect.Projection = Matrix.CreatePerspectiveFieldOfView( MathHelper.ToRadians(60.0f),

aspectRatio, 1.0f, 500.0f);

Ballistic Demo

Other Particle Types// Laser//ammos.Mass = 0.1f; // 0.1kg - almost no weight//ammos.Velocity = new Vector3(0.0f, 0.0f, 100.0f);// 100m/s//ammos.Acceleration = new Vector3(0.0f, 0.0f, 0.0f); //No gravity//ammos.Damping = 0.99f;

// Pistol//ammos.Mass = 2.0f; // 2.0kg //ammos.Velocity = new Vector3(0.0f, 0.0f, 35.0f);// 35m/s//ammos.Acceleration = new Vector3(0.0f, -1.0f, 0.0f); //ammos.Damping = 0.99f;

// Fireball//ammos.Mass = 1.0f; // 1.0kg //ammos.Velocity = new Vector3(0.0f, 0.0f, 10.0f);// 10m/s//ammos.Acceleration = new Vector3(0.0f, 0.6f, 0.0f);// Floats up//ammos.Damping = 0.9f;

Multiple Particles in Scene

Particle Array

const int ammoMax = 10;Particle[] ammos;

ammos = new Particle[ammoMax];

Declared as a field of the Game class

Created in Initialize()

Timer in XNAMouseState mouse = Mouse.GetState();m_gameTime = gameTime;if ((mouse.LeftButton == ButtonState.Pressed)&& (m_gameTime.TotalGameTime.TotalMilliseconds - lastTime > 200)){ // Do your mouse state logic here lastTime = m_gameTime.TotalGameTime.TotalMilliseconds; fire(gametime);}

Updating the Particlesfloat duration =

gameTime.ElapsedGameTime.Milliseconds / (1000.0f);for (int i = 0; i < ammoMax; i++){ if (ammos[i] != null) { if (ammos[i].Position.Y < 0) ammos[i] = null; else ammos[i].Integrate(duration); }}

Firing the Particles private void fire(GameTime gametime) { for (int i = 0; i < ammoMax; i++) { if (ammos[i] == null) { ammos[i] = new Particle(); // Artillery ammos[i].Mass = 200.0f; // 200.0kg ammos[i].Velocity = new Vector3(0.0f, 30.0f, 40.0f); ammos[i].Acceleration =

new Vector3(0.0f, -20.0f, 0.0f); ammos[i].Damping = 0.99f; ammos[i].Position = new Vector3(0.0f, 1.5f, 0.0f); ammos[i].clearAccumulator(); break; } }

Drawing the Particles (1/2)protected override void Draw(GameTime gameTime){ ... ... ... draw_lines(device); for(int i =0 ; i < ammoMax; i++) if(ammos[i] != null) draw_ammo(i); base.Draw(gameTime);}

Drawing the Particles (2/2)private void draw_ammo(int i){ foreach (ModelMesh mesh in myModel.Meshes) { // Draw the current mesh foreach (BasicEffect eff in mesh.Effects) { eff.World = Matrix.CreateScale(0.03f); eff.World *=

Matrix.CreateTranslation(ammos[i].Position); eff.View = effect.View; eff.Projection = effect.Projection; eff.EnableDefaultLighting(); } mesh.Draw(); }}

Multiple Particle Demo