md` ## Boids Flocking code from Processing \`\`\`\` Flock flock; void setup() { size(640, 360); flock = new Flock(); // Add an initial set of boids into the system for (int i = 0; i < 150; i++) { flock.addBoid(new Boid(width/2,height/2)); } } void draw() { background(50); flock.run(); } // Add a new boid into the System void mousePressed() { flock.addBoid(new Boid(mouseX,mouseY)); } // The Flock (a list of Boid objects) class Flock { ArrayList boids; // An ArrayList for all the boids Flock() { boids = new ArrayList(); // Initialize the ArrayList } void run() { for (Boid b : boids) { b.run(boids); // Passing the entire list of boids to each boid individually } } void addBoid(Boid b) { boids.add(b); } } // The Boid class class Boid { PVector position; PVector velocity; PVector acceleration; float r; float maxforce; // Maximum steering force float maxspeed; // Maximum speed Boid(float x, float y) { acceleration = new PVector(0, 0); // This is a new PVector method not yet implemented in JS // velocity = PVector.random2D(); // Leaving the code temporarily this way so that this example runs in JS float angle = random(TWO_PI); velocity = new PVector(cos(angle), sin(angle)); position = new PVector(x, y); r = 2.0; maxspeed = 2; maxforce = 0.03; } void run(ArrayList boids) { flock(boids); update(); borders(); render(); } void applyForce(PVector force) { // We could add mass here if we want A = F / M acceleration.add(force); } // We accumulate a new acceleration each time based on three rules void flock(ArrayList boids) { PVector sep = separate(boids); // Separation PVector ali = align(boids); // Alignment PVector coh = cohesion(boids); // Cohesion // Arbitrarily weight these forces sep.mult(1.5); ali.mult(1.0); coh.mult(1.0); // Add the force vectors to acceleration applyForce(sep); applyForce(ali); applyForce(coh); } // Method to update position void update() { // Update velocity velocity.add(acceleration); // Limit speed velocity.limit(maxspeed); position.add(velocity); // Reset accelertion to 0 each cycle acceleration.mult(0); } // A method that calculates and applies a steering force towards a target // STEER = DESIRED MINUS VELOCITY PVector seek(PVector target) { PVector desired = PVector.sub(target, position); // A vector pointing from the position to the target // Scale to maximum speed desired.normalize(); desired.mult(maxspeed); // Above two lines of code below could be condensed with new PVector setMag() method // Not using this method until Processing.js catches up // desired.setMag(maxspeed); // Steering = Desired minus Velocity PVector steer = PVector.sub(desired, velocity); steer.limit(maxforce); // Limit to maximum steering force return steer; } void render() { // Draw a triangle rotated in the direction of velocity float theta = velocity.heading2D() + radians(90); // heading2D() above is now heading() but leaving old syntax until Processing.js catches up fill(200, 100); stroke(255); pushMatrix(); translate(position.x, position.y); rotate(theta); beginShape(TRIANGLES); vertex(0, -r*2); vertex(-r, r*2); vertex(r, r*2); endShape(); popMatrix(); } // Wraparound void borders() { if (position.x < -r) position.x = width+r; if (position.y < -r) position.y = height+r; if (position.x > width+r) position.x = -r; if (position.y > height+r) position.y = -r; } // Separation // Method checks for nearby boids and steers away PVector separate (ArrayList boids) { float desiredseparation = 25.0f; PVector steer = new PVector(0, 0, 0); int count = 0; // For every boid in the system, check if it's too close for (Boid other : boids) { float d = PVector.dist(position, other.position); // If the distance is greater than 0 and less than an arbitrary amount (0 when you are yourself) if ((d > 0) && (d < desiredseparation)) { // Calculate vector pointing away from neighbor PVector diff = PVector.sub(position, other.position); diff.normalize(); diff.div(d); // Weight by distance steer.add(diff); count++; // Keep track of how many } } // Average -- divide by how many if (count > 0) { steer.div((float)count); } // As long as the vector is greater than 0 if (steer.mag() > 0) { // First two lines of code below could be condensed with new PVector setMag() method // Not using this method until Processing.js catches up // steer.setMag(maxspeed); // Implement Reynolds: Steering = Desired - Velocity steer.normalize(); steer.mult(maxspeed); steer.sub(velocity); steer.limit(maxforce); } return steer; } // Alignment // For every nearby boid in the system, calculate the average velocity PVector align (ArrayList boids) { float neighbordist = 50; PVector sum = new PVector(0, 0); int count = 0; for (Boid other : boids) { float d = PVector.dist(position, other.position); if ((d > 0) && (d < neighbordist)) { sum.add(other.velocity); count++; } } if (count > 0) { sum.div((float)count); // First two lines of code below could be condensed with new PVector setMag() method // Not using this method until Processing.js catches up // sum.setMag(maxspeed); // Implement Reynolds: Steering = Desired - Velocity sum.normalize(); sum.mult(maxspeed); PVector steer = PVector.sub(sum, velocity); steer.limit(maxforce); return steer; } else { return new PVector(0, 0); } } // Cohesion // For the average position (i.e. center) of all nearby boids, calculate steering vector towards that position PVector cohesion (ArrayList boids) { float neighbordist = 50; PVector sum = new PVector(0, 0); // Start with empty vector to accumulate all positions int count = 0; for (Boid other : boids) { float d = PVector.dist(position, other.position); if ((d > 0) && (d < neighbordist)) { sum.add(other.position); // Add position count++; } } if (count > 0) { sum.div(count); return seek(sum); // Steer towards the position } else { return new PVector(0, 0); } } } \`\`\`\` `