// needed for the vehicle to travel the curve

let t = 0

​

// The current portion of the curve the car is

// travelling along. ab and bc are the end points

// and will be the midpoints between (a,b) and (b,c) 

// b is the control point

let curve = { a:  undefined,

              ab: undefined,

              b:  undefined,

              bc: undefined,

              c:  undefined }

​

​

// Just a line with an arrowhead

function arrow(x1, y1, x2, y2) {

  line(x1, y1, x2, y2)

  let r = 8               // Arrowhead radius

  let u = createVector(x2-x1, y2-y1).normalize()

  let a = 0.94,  b = 0.34 // Arrowhead half angle

  beginShape()

  vertex( x2 + (-a * u.x - b * u.y) * r,

          y2 + ( b * u.x - a * u.y) * r )

  vertex( x2, y2 )

  vertex( x2 + (-a * u.x + b * u.y) * r,

          y2 + (-b * u.x - a * u.y) * r )

  endShape()

}

​

// Draw a pointer at position p,

// pointing in direction u

function ship(p, u) {

  u.mult(8)

  let p1 = wrap( p5.Vector.sub(p, u) )

  let p2 = wrap( p5.Vector.add(p, u) )

  if(p1.dist(p2) > 20) {

    return

  }

  stroke("orange")

  strokeWeight(2)

  arrow(p1.x, p1.y, p2.x, p2.y)  

}

​

// The ship's position and direction on

// the quadratic bezier curve

// [a, c] = start and end points, b = control pt,

// 0 <= t <= 1 

function where_at(a, b, c, t) {

  let w = p5.Vector.lerp(a, b, t)

  let x = p5.Vector.lerp(b, c, t)

  let y = w.lerp(x, t)

  x.sub(w).normalize()

  ship(y, x)

}

​

function next_point(prv) {

  let ang = random(PI)

  return p5.Vector.fromAngle(ang).mult(80).add(prv)

}

​

function advance() {

  t = 0

  curve.a = curve.b

  curve.b = curve.c

  curve.c = next_point(curve.c)

  curve.ab = curve.bc

  curve.bc = p5.Vector.lerp(curve.b, curve.c, 0.5)

}

​

function wrap(p) {

  return createVector( (p.x + width) % width,

                       (p.y + height) % height )

}

​

function setup() {

  createCanvas(400, 400);

  curve.a = createVector(200, 200)

  curve.b = next_point(curve.a)

  curve.c = next_point(curve.b)

  curve.ab = p5.Vector.lerp(curve.a, curve.b, 0.5)

  curve.bc = p5.Vector.lerp(curve.b, curve.c, 0.5)

}

​

function draw() {

  background(0);

  stroke(200)

  strokeWeight(3)

  point(wrap(curve.a))

  point(wrap(curve.b))

  point(wrap(curve.c))

  where_at(curve.ab, curve.b, curve.bc, t)

  t = t + 0.02

  if(t > 1) advance()

}

​

​

​

​