A sketch to get a timeline that moves forward and backward when you move the mouse.

Timeline.pde

int year = 0;
int y = 0;
int spacing = 50;

void setup(){
  size(500,800);
  background(0);
  textSize(25);
  fill(255,255,255);
  for (int i = year; i<2018; i=i+25){
  text(i, 10, y+25);
  y = y + spacing;
  }
}

void draw(){
}

void mouseMoved(){
  int x = 0;
  y = 10;
  if (mouseY>750 && year<1950){
    year = year + 25;
    y=0;
    background(0);
    fill(255,255,255);
    for (int i = year; i<2018; i=i+25){
      print(year + " ");
      if(i<0) {
         text(abs(i) + " BC", 10, y+25);
       } else {
         text(abs(i), 10, y+25);
       }
      x = x+25;
      y = y +spacing;
    }
  }   
  if (mouseY<50 && year>-5000){
    y=0;
     year = year - 25;
     background(0);
     for (int i = year; i<2018; i=i+25){
       print(year + " ");
       if(i<0) {
         text(abs(i) + " BC", 10, y+25);
       } else {
         text(abs(i), 10, y+25);
       }
       x = x+25;
       y = y+spacing;
     }
   }
}