Use spring animation for presenting sheet

Sources/SheetController/SheetContainerPresentationAnimationController.swift

@@ -31,22 +31,26 @@ class SheetContainerPresentationAnimationController: NSObject, UIViewControllerA
         container.addSubview(dimmingView)
         container.addSubview(toVC.view)
         
-        toVC.view.transform = CGAffineTransform(translationX: 0, y: toVC.initialConstant)
+        let initialConstant = toVC.initialConstant
+        toVC.topConstraint.constant = toVC.view.bounds.height
+        toVC.view.layoutIfNeeded()
         
         let duration = transitionDuration(using: transitionContext)
-        UIView.animate(withDuration: duration, animations: {
+        let velocity = 1 / CGFloat(duration)
+        UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: 0.65, initialSpringVelocity: velocity, options: []) {
             // we animate the dimming view's frame so that it doesn't go under the content view, in case there's a transparent background
             // we also extend the dimming view under any rounded corners the content view has
-            dimmingView.frame = CGRect(x: 0, y: 0, width: dimmingView.bounds.width, height: toVC.initialConstant + toVC.content.view.layer.cornerRadius)
+            dimmingView.frame = CGRect(x: 0, y: 0, width: dimmingView.bounds.width, height: initialConstant + toVC.content.view.layer.cornerRadius)
             dimmingView.alpha = toVC.dimmingView.alpha
-            toVC.view.transform = .identity
-        }, completion: { (finished) in
+            toVC.topConstraint.constant = initialConstant
+            toVC.view.layoutIfNeeded()
+        } completion: { (finished) in
             dimmingView.removeFromSuperview()
             toVC.dimmingView.isHidden = false
             
             toVC.view.frame = finalFrame
             transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
-        })
+        }
 
     }