Light Painting

var cells = [];

var cellW = 15;

var cellH = 15;

var nbCellW;

var nbCellH;

​

function setup() {

  createCanvas(600, 600);

  rectMode(CENTER);

  colorMode(HSB, 1);

  nbCellW = floor(width / cellW);

  nbCellH = floor(height / cellH);

  for (var i = 0; i < nbCellW*nbCellH; i ++) {

    cells.push(createVector(0, 0));

  }

}

​

function  draw() {

  var deltaMouse = createVector(mouseX - pmouseX, mouseY - pmouseY);

  for (var i = 0; i < nbCellW; i ++) {

    for (var j = 0; j < nbCellH; j ++) {

      var k = i+j*nbCellW;

      var x =  cellW * i + cellW/2;

      var y =  cellH * j + cellH/2;

      var d = Math.max(1, dist(mouseX, mouseY, x, y));

      deltaMouse.normalize();

      deltaMouse.mult(1/(d*30));

      cells[k].add(deltaMouse);

      cells[k].limit(10);

      var h = map(cells[k].heading(), -PI, PI, 0, 1);

      var b = min(cells[k].mag()*100, 10);

      fill(h, 1, b);

      rect(x, y, cellW, cellH);

      cells[k].mult(.98);

    }

  }

}

​