min()max() Example

MinMax.swift

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        
        // Move ContainerView based on pagination from custom pagingScrollView
        if scrollView == pagingScrollView {
            
            // Calculate offset
            let offset = (self.view.frame.size.height - bottomPeekMargin) - scrollView.contentOffset.y

            // Overlay value (interpolates between 0.0 and 1.0 for end value)
            // Note to self: contentOffset divided by endValue (where you end the animation)
            let overlayAlpha = min(1, max(0, scrollView.contentOffset.y / (self.view.frame.size.height - bottomPeekMargin)))
            
            // Set overlay value
            self.darkOverlayView.alpha = overlayAlpha
            
            // Freeze when open
            if offset >= 0 {
                // Offset view based on scrollView
                containerView.frame.origin.y = offset
            }
        }
    }