let arrows = []; let angle = [];

let r = size/2; 

​

function setup() {

  createCanvas(600, 400);

  cols = width/size;

  rows = height/size;

  angleMode(DEGREES);

  for (let i=0; i<cols; i++) {

    arrows[i] = [];

    angle[i] = [];

    for (let j=0; j<rows; j++) {

      angle[i][j] = random(0, 360);

      arrows[i][j] = createVector(cos(angle[i][j]), sin(angle[i][j]));

    }

  }

​

}

​

function draw() {

  background(255);

  stroke(0);

  for (let i=0; i<cols; i++) {

    for (let j=0; j<rows; j++) {

      rect(i*size, j*size, size, size);

      // text(round(angle[i][j], 2), size/2+i*size, size/2+j*size);

      let pt0 = createVector(size/2+ i*size, size/2+j*size);

      let pt1 = createVector(r*arrows[i][j].x, r*arrows[i][j].y);

      line(pt0.x, pt0.y, pt0.x + pt1.x, pt0.y + pt1.y);

      ellipse(pt0.x + pt1.x, pt0.y + pt1.y, 5, 5);

​

    }

  }

}