sclass IIVerticalSplit extends Meta implements IIntegralImage {
  // y coordinate of split point
  int splitPoint; 
  
  // a and b must have same width
  
  // [0; splitPoint)
  RegisteredReference<IIntegralImage> a = new(this);
  
  // [splitPoint; height)
  RegisteredReference<IIntegralImage> b = new(this);
  
  *() {}
  *(IIntegralImage contents) {
    this.contents.set(contents);
  }
  
  public getWidth() { ret a->getWidth(); }
  public simplyCached int getHeight() { ret a->getHeight()+b->getHeight(); }

  public double getIntegralValue(int x, int y, int channel) {
    if (y < splitPoint)
      ret a->getIntegralValue(x, y, channel);
    else
      ret b->getIntegralValue(x, y-splitPoint, channel);
  }
    
  public double getIntegralValue(int x, int y) {
    if (y < splitPoint)
      ret a->getIntegralValue(x, y);
    else
      ret b->getIntegralValue(x, y-splitPoint);
  }
  
  public BufferedImage getBufferedImage() {
    BufferedImage img = newBufferedImage(getWidth(), getHeight());
    var g = graphics(img);
    a->drawAt(g, 0, 0);
    b->drawAt(g, 0, splitPoint);
    ret img;
  }
}