canvas野猪奔跑动画

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var flock;
var gif = [];
var index = 1;
var totalHogs = 1;
var HogCount = Math.floor(Math.random() * (50 - 30 + 1)) + 30;

function windowResized(){
  resizeCanvas(windowWidth, windowHeight);
}

function preload() {
  for(var i = 1; i < 31; i++){
    gif[i] = loadImage("https://s3-us-west-2.amazonaws.com/s.cdpn.io/383755/pig" + i + ".png");
  }
}

function setup() {
  createCanvas(windowWidth, windowHeight);
  
  flock = new Flock();
  // Add an initial set of Hogs into the system
  for (var i = 0; i < HogCount; i++) {
    var b = new Hog(width/2,height/2);
    flock.addHog(b);
  }
}

function draw() {
  background(140,104,78);
  totalHogs++;
  if(totalHogs >= 101){
    totalHogs = 1;
  }
  index++;
  if(index >= 31){
    index = 1;
  }
  flock.run();
}

// Flock object manages the array of all the Hogs
function Flock() {
  // An array for all the Hogs
  this.Hogs = []; // Initialize the array
}

Flock.prototype.run = function() {
  for (var i = 0; i < this.Hogs.length; i++) {
    this.Hogs[i].run(this.Hogs);  // Passing the entire list of Hogs to each Hog individually
  }
}

Flock.prototype.addHog = function(b) {
  this.Hogs.push(b);
}

// Hog class
// Methods for Separation, Cohesion, Alignment added
function Hog(x,y) {
  this.acceleration = createVector(0,0);
  this.velocity = createVector(random(-1,1),random(-1,1));
  this.position = createVector(x,y);
  this.r = 3.0;
  this.maxspeed = 5;    // Maximum speed
  this.maxforce = 0.05; // Maximum steering force
}

Hog.prototype.run = function(Hogs) {
  this.flock(Hogs);
  this.update();
  this.borders();
  this.render();
}

Hog.prototype.applyForce = function(force) {
  // We could add mass here if we want A = F / M
  this.acceleration.add(force);
}

// We accumulate a new acceleration each time based on three rules
Hog.prototype.flock = function(Hogs) {
  var sep = this.separate(Hogs);   // Separation
  var ali = this.align(Hogs);      // Alignment
  var coh = this.cohesion(Hogs);   // Cohesion
  // Arbitrarily weight these forces
  sep.mult(1.5);
  ali.mult(1.0);
  coh.mult(1.0);
  // Add the force vectors to acceleration
  this.applyForce(sep);
  this.applyForce(ali);
  this.applyForce(coh);
}

// Method to update location
Hog.prototype.update = function() {
  // Update velocity
  this.velocity.add(this.acceleration);
  // Limit speed
  this.velocity.limit(this.maxspeed);
  this.position.add(this.velocity);
  // Reset accelertion to 0 each cycle
  this.acceleration.mult(0);
}

// A method that calculates and applies a steering force towards a target
// STEER = DESIRED MINUS VELOCITY
Hog.prototype.seek = function(target) {
  var desired = p5.Vector.sub(target,this.position);  // A vector pointing from the location to the target
  // Normalize desired and scale to maximum speed
  desired.normalize();
  desired.mult(this.maxspeed);
  // Steering = Desired minus Velocity
  var steer = p5.Vector.sub(desired,this.velocity);
  steer.limit(this.maxforce);  // Limit to maximum steering force
  return steer;
}

Hog.prototype.render = function() {
    var theta = this.velocity.heading() + radians(90);
    push();
    translate(this.position.x,this.position.y);
    rotate((theta) - 0);
    image(gif[index], 0, 0, 25, 35);
    pop();
}

// Wraparound
Hog.prototype.borders = function() {
  if (this.position.x < -this.r)  this.position.x = width +this.r;
  if (this.position.y < -this.r)  this.position.y = height+this.r;
  if (this.position.x > width +this.r) this.position.x = -this.r;
  if (this.position.y > height+this.r) this.position.y = -this.r;
}

// Separation
// Method checks for nearby Hogs and steers away
Hog.prototype.separate = function(Hogs) {
  var desiredseparation = 55.0;
  var steer = createVector(0,0);
  var count = 0;
  // For every Hog in the system, check if it's too close
  for (var i = 0; i < Hogs.length; i++) {
    var d = p5.Vector.dist(this.position,Hogs[i].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
      var diff = p5.Vector.sub(this.position,Hogs[i].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(count);
  }

// As long as the vector is greater than 0
  if (steer.mag() > 0) {
    // Implement Reynolds: Steering = Desired - Velocity
    steer.normalize();
    steer.mult(this.maxspeed);
    steer.sub(this.velocity);
    steer.limit(this.maxforce);
  }
  return steer;
}

// Alignment
// For every nearby Hog in the system, calculate the average velocity
Hog.prototype.align = function(Hogs) {
  var neighbordist = 50;
  var sum = createVector(0,0);
  var count = 0;
  for (var i = 0; i < Hogs.length; i++) {
    var d = p5.Vector.dist(this.position,Hogs[i].position);
    if ((d > 0) && (d < neighbordist)) {
      sum.add(Hogs[i].velocity);
      count++;
    }
  }
  if (count > 0) {
    sum.div(count);
    sum.normalize();
    sum.mult(this.maxspeed);
    var steer = p5.Vector.sub(sum,this.velocity);
    steer.limit(this.maxforce);
    return steer;
  } else {
    return createVector(0,0);
  }
}

// Cohesion
// For the average location (i.e. center) of all nearby Hogs, calculate steering vector towards that location
Hog.prototype.cohesion = function(Hogs) {
  var neighbordist = 50;
  var sum = createVector(0,0);   // Start with empty vector to accumulate all locations
  var count = 0;
  for (var i = 0; i < Hogs.length; i++) {
    var d = p5.Vector.dist(this.position,Hogs[i].position);
    if ((d > 0) && (d < neighbordist)) {
      sum.add(Hogs[i].position); // Add location
      count++;
    }
  }
  if (count > 0) {
    sum.div(count);
    return this.seek(sum);  // Steer towards the location
  } else {
    return createVector(0,0);
  }
}

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