gistfile1.m

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    float y = scrollView.contentOffset.y;

////// parallax
    CGAffineTransform transform;
    BOOL clip = YES;
    y -= 320;
    if (y < -320) {
        float const required_scale = y / -320;
        transform = CGAffineTransformMakeTranslation(0, (y+320.f)/2.f);
        transform = CGAffineTransformScale(transform, required_scale, required_scale);
        clip = NO;
    } else
        transform = CGAffineTransformMakeTranslation(0, (y+320.f)*3.f/5.f);
    stretchyView.transform = transform;
    stretchyView.superview.clipsToBounds = clip;
}