float tt = 50; // change with time

void setup() {
  size(800, 600);
  noFill();
  stroke(255);
}

void draw() {
  background(0);
  float tx = 0; // change with horizontal position
  beginShape();
  for (int x = 0; x < width - 1; x++) {    
    float y = 150 + noise(tx, tt) * 200;
    vertex(x, y);
    tx += 0.01;
  }
  endShape();
  tt += 0.003;
}