var lastMouseY = [];

​

var pos=0;

​

function setup() {

  createCanvas(600, 600);

}

​

function draw() {

  background("cornflowerblue");

  noFill();

  stroke("yellow");

  strokeWeight(5);

  beginShape();

  for(var i=0; i<100; i++){

    vertex(lastMouseX[i], lastMouseY[i]);

  }

  endShape();

}

​

function mouseMoved(){

  if(pos==100){

    for(var i=0; i<100; i++){

      lastMouseX[i] = lastMouseX[i+1]; 

      lastMouseY[i] = lastMouseY[i+1];

    }

  } else{pos++;}

  lastMouseX[pos] = mouseX;

  lastMouseY[pos] = mouseY;

}