let sx, sy;

​

// Where line is now

let x, y;

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  // Start and end line at same point

  sx = 0.05*width;

  sy = 0;

  x = sx;

  y = sy;

}

​

function draw() {

  background(255);

  // Restart the line

  if(x > width) {

     x = sx;

     y = sy;    

  }

  // Move endpoint of line

  x += 0.1;

  y += 0.05;

  // Draw the line

  strokeWeight(5);

  line(sx, sy, x, y);

}