initial pass at MotionController rework

Motion.xcodeproj/project.pbxproj

@@ -37,7 +37,7 @@
 		96AEB6A31EE4610F009A3BE0 /* MotionPlugin.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB67D1EE4610F009A3BE0 /* MotionPlugin.swift */; };
 		96AEB6A41EE4610F009A3BE0 /* MotionStringConvertible.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB67E1EE4610F009A3BE0 /* MotionStringConvertible.swift */; };
 		96AEB6A51EE4610F009A3BE0 /* MotionTargetState.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB67F1EE4610F009A3BE0 /* MotionTargetState.swift */; };
-		96AEB6A61EE4610F009A3BE0 /* MotionTypes.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB6801EE4610F009A3BE0 /* MotionTypes.swift */; };
+		96AEB6A61EE4610F009A3BE0 /* MotionViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB6801EE4610F009A3BE0 /* MotionViewController.swift */; };
 		96AEB6A71EE4610F009A3BE0 /* Lexer.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB6821EE4610F009A3BE0 /* Lexer.swift */; };
 		96AEB6A81EE4610F009A3BE0 /* Nodes.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB6831EE4610F009A3BE0 /* Nodes.swift */; };
 		96AEB6A91EE4610F009A3BE0 /* Parser.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB6841EE4610F009A3BE0 /* Parser.swift */; };
@@ -48,6 +48,7 @@
 		96AEB6AE1EE4610F009A3BE0 /* IgnoreSubviewModifiersPreprocessor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB68A1EE4610F009A3BE0 /* IgnoreSubviewModifiersPreprocessor.swift */; };
 		96AEB6AF1EE4610F009A3BE0 /* MatchPreprocessor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB68B1EE4610F009A3BE0 /* MatchPreprocessor.swift */; };
 		96AEB6B01EE4610F009A3BE0 /* SourcePreprocessor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96AEB68C1EE4610F009A3BE0 /* SourcePreprocessor.swift */; };
+		96E49A401EEA08F8006D5A93 /* MotionTransitionObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96E49A3F1EEA08F8006D5A93 /* MotionTransitionObserver.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -80,7 +81,7 @@
 		96AEB67D1EE4610F009A3BE0 /* MotionPlugin.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionPlugin.swift; sourceTree = "<group>"; };
 		96AEB67E1EE4610F009A3BE0 /* MotionStringConvertible.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionStringConvertible.swift; sourceTree = "<group>"; };
 		96AEB67F1EE4610F009A3BE0 /* MotionTargetState.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionTargetState.swift; sourceTree = "<group>"; };
-		96AEB6801EE4610F009A3BE0 /* MotionTypes.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionTypes.swift; sourceTree = "<group>"; };
+		96AEB6801EE4610F009A3BE0 /* MotionViewController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionViewController.swift; sourceTree = "<group>"; };
 		96AEB6821EE4610F009A3BE0 /* Lexer.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Lexer.swift; sourceTree = "<group>"; };
 		96AEB6831EE4610F009A3BE0 /* Nodes.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Nodes.swift; sourceTree = "<group>"; };
 		96AEB6841EE4610F009A3BE0 /* Parser.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Parser.swift; sourceTree = "<group>"; };
@@ -95,6 +96,7 @@
 		96C98DDD1E424B9000B22906 /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		96C98DE21E43809D00B22906 /* LICENSE */ = {isa = PBXFileReference; lastKnownFileType = text; path = LICENSE; sourceTree = "<group>"; };
 		96C98DED1E438A5700B22906 /* Motion.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = Motion.h; sourceTree = "<group>"; };
+		96E49A3F1EEA08F8006D5A93 /* MotionTransitionObserver.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MotionTransitionObserver.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -207,7 +209,8 @@
 				96AEB67D1EE4610F009A3BE0 /* MotionPlugin.swift */,
 				96AEB67E1EE4610F009A3BE0 /* MotionStringConvertible.swift */,
 				96AEB67F1EE4610F009A3BE0 /* MotionTargetState.swift */,
-				96AEB6801EE4610F009A3BE0 /* MotionTypes.swift */,
+				96AEB6801EE4610F009A3BE0 /* MotionViewController.swift */,
+				96E49A3F1EEA08F8006D5A93 /* MotionTransitionObserver.swift */,
 				96AEB6811EE4610F009A3BE0 /* Parser */,
 				96AEB6861EE4610F009A3BE0 /* Preprocessors */,
 			);
@@ -308,9 +311,10 @@
 				96AEB6961EE4610F009A3BE0 /* Motion+CAMediaTimingFunction.swift in Sources */,
 				96AEB6941EE4610F009A3BE0 /* Motion+Array.swift in Sources */,
 				96AEB6951EE4610F009A3BE0 /* Motion+CALayer.swift in Sources */,
-				96AEB6A61EE4610F009A3BE0 /* MotionTypes.swift in Sources */,
+				96AEB6A61EE4610F009A3BE0 /* MotionViewController.swift in Sources */,
 				96AEB68E1EE4610F009A3BE0 /* MotionCoreAnimationViewContext.swift in Sources */,
 				96AEB6921EE4610F009A3BE0 /* MotionDebugView.swift in Sources */,
+				96E49A401EEA08F8006D5A93 /* MotionTransitionObserver.swift in Sources */,
 				96AEB6A01EE4610F009A3BE0 /* MotionIndependentController.swift in Sources */,
 				96AEB6AA1EE4610F009A3BE0 /* Regex.swift in Sources */,
 				96AEB6901EE4610F009A3BE0 /* MotionViewPropertyViewContext.swift in Sources */,

Sources/Motion.swift

@@ -58,11 +58,13 @@ public class Motion: MotionController {
     public internal(set) var isPresenting = true
 
     /// Progress of the current transition, 0 if a transition is not happening.
-    public override var progress: Double {
+    public override var elapsedTime: TimeInterval {
         didSet {
-            if isTransitioning {
-                transitionContext?.updateInteractiveTransition(CGFloat(progress))
+            guard isTransitioning else {
+                return
             }
+            
+            transitionContext?.updateInteractiveTransition(CGFloat(elapsedTime))
         }
     }
 
@@ -155,7 +157,7 @@ public extension Motion {
     }
 }
 
-internal extension Motion {
+fileprivate extension Motion {
     /// Starts the transition animation.
     func start() {
         guard isTransitioning else {
@@ -165,51 +167,25 @@ internal extension Motion {
         prepareViewControllers()
         prepareSnapshotView()
         prepareForTransition()
-        prepareMotionContext()
+        prepareContext()
         prepareToView()
         prepareViewHierarchy()
-
         processContext()
         prepareForAnimation()
-
-        context.hide(view: toView)
-
-        #if os(tvOS)
-            animate()
-        #else
-            if isNavigationController {
-                // When animating within navigationController, we have to dispatch later into the main queue.
-                // otherwise snapshots will be pure white. Possibly a bug with UIKit
-                DispatchQueue.main.async { [weak self] in
-                    self?.animate()
-                }
-            } else {
-                animate()
-            }
-        #endif
+        processForAnimation()
     }
+}
 
+internal extension Motion {
     override func animate() {
         context.unhide(view: toView)
         
-        if let containerBackgroundColor = containerBackgroundColor {
-            container.backgroundColor = containerBackgroundColor
-        } else if !toOverFullScreen && !fromOverFullScreen {
-            container.backgroundColor = toView.backgroundColor
-        }
-        
-        if fromOverFullScreen {
-            insertToViewFirst = true
-        }
-    
-        for animator in animators {
-            if let animator = animator as? MotionHasInsertOrder {
-                animator.insertToViewFirst = insertToViewFirst
-            }
-        }
+        updateContainerBackgroundColor()
+        updateInsertOrder()
         
         super.animate()
-        fullScreenSnapshot!.removeFromSuperview()
+        
+        fullScreenSnapshot?.removeFromSuperview()
     }
     
     override func complete(finished: Bool) {
@@ -344,7 +320,7 @@ fileprivate extension Motion {
     }
     
     /// Prepares the MotionContext instance.
-    func prepareMotionContext() {
+    func prepareContext() {
         context.loadViewAlpha(rootView: toView)
         context.loadViewAlpha(rootView: fromView)
         container.addSubview(toView)
@@ -370,6 +346,52 @@ internal extension Motion {
         super.prepareForTransition()
         insert(preprocessor: DefaultAnimationPreprocessor(motion: self), before: DurationPreprocessor.self)
     }
+    
+    override func prepareForAnimation() {
+        super.prepareForAnimation()
+        context.hide(view: toView)
+    }
+}
+
+fileprivate extension Motion {
+    /// Processes the animations.
+    func processForAnimation() {
+        #if os(tvOS)
+            animate()
+        #else
+            if isNavigationController {
+                // When animating within navigationController, we have to dispatch later into the main queue.
+                // otherwise snapshots will be pure white. Possibly a bug with UIKit
+                DispatchQueue.main.async { [weak self] in
+                    self?.animate()
+                }
+            } else {
+                animate()
+            }
+        #endif
+    }
+}
+
+fileprivate extension Motion {
+    /// Updates the container background color.
+    func updateContainerBackgroundColor() {
+        if let v = containerBackgroundColor {
+            container.backgroundColor = v
+        } else if !toOverFullScreen && !fromOverFullScreen {
+            container.backgroundColor = toView.backgroundColor
+        }
+    }
+    
+    /// Updates the insertToViewFirst boolean for animators.
+    func updateInsertOrder() {
+        if fromOverFullScreen {
+            insertToViewFirst = true
+        }
+        
+        for v in animators {
+            (v as? MotionHasInsertOrder)?.insertToViewFirst = insertToViewFirst
+        }
+    }
 }
 
 internal extension Motion {
@@ -418,23 +440,31 @@ internal extension Motion {
     }
 }
 
-// MARK: UIKit Protocol Conformance
-
-/*****************************
- * UIKit protocol extensions *
- *****************************/
-
 extension Motion: UIViewControllerAnimatedTransitioning {
+    /**
+     The animation method that is used to coordinate the transition.
+     - Parameter using transitionContext: A UIViewControllerContextTransitioning.
+     */
     public func animateTransition(using context: UIViewControllerContextTransitioning) {
-    guard !isTransitioning else { return }
+        guard !isTransitioning else {
+            return
+        }
+        
         transitionContext = context
         fromViewController = fromViewController ?? context.viewController(forKey: .from)
         toViewController = toViewController ?? context.viewController(forKey: .to)
         transitionContainer = context.containerView
+        
         start()
     }
+    
+    /**
+     Returns the transition duration time interval.
+     - Parameter using transitionContext: An optional UIViewControllerContextTransitioning.
+     - Returns: A TimeInterval that is the total animation time including delays.
+     */
     public func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
-    return 0.375 // doesn't matter, real duration will be calculated later
+        return 0 // Will be updated dynamically.
     }
     
     public func animationEnded(_ transitionCompleted: Bool) {
@@ -442,11 +472,14 @@ extension Motion: UIViewControllerAnimatedTransitioning {
     }
 }
 
-extension Motion:UIViewControllerTransitioningDelegate {
-  var interactiveTransitioning: UIViewControllerInteractiveTransitioning? {
-    return forceNonInteractive ? nil : self
+extension Motion {
+    /// A reference to the interactive transitioning.
+    fileprivate var interactiveTransitioning: UIViewControllerInteractiveTransitioning? {
+        return self
     }
+}
 
+extension Motion: UIViewControllerTransitioningDelegate {
     public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
         self.isPresenting = true
         self.fromViewController = fromViewController ?? presenting
@@ -480,7 +513,7 @@ extension Motion: UIViewControllerInteractiveTransitioning {
 
 extension Motion: UINavigationControllerDelegate {
     public func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
-    self.isPresenting = operation == .push
+        self.isPresenting = .push == operation
         self.fromViewController = fromViewController ?? fromVC
         self.toViewController = toViewController ?? toVC
         self.isNavigationController = true
@@ -503,12 +536,15 @@ extension Motion: UITabBarControllerDelegate {
     
     public func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
         isAnimating = true
+        
         let fromVCIndex = tabBarController.childViewControllers.index(of: fromVC)!
         let toVCIndex = tabBarController.childViewControllers.index(of: toVC)!
+        
         self.isPresenting = toVCIndex > fromVCIndex
         self.fromViewController = fromViewController ?? fromVC
         self.toViewController = toViewController ?? toVC
         self.isTabBarController = true
+        
         return self
     }
 }

Sources/MotionController.swift

@@ -28,107 +28,168 @@
 
 import UIKit
 
-/// Base class for managing a Motion transition
 public class MotionController: NSObject {
-  // MARK: Properties
-  /// context object holding transition informations
+    /// A reference to the MotionContext.
     public internal(set) var context: MotionContext!
-  /// whether or not we are handling transition interactively
-  public var interactive: Bool {
-    return displayLink == nil
+
+    /// A boolean indicating whether the transition interactive or not.
+    public var isInteractive: Bool {
+        return nil == displayLink
     }
-  /// progress of the current transition. 0 if no transition is happening
-  public internal(set) var progress: Double = 0 {
+    
+    /// Progress of the current transition. 0 if no transition is happening.
+    public internal(set) var elapsedTime: TimeInterval = 0 {
         didSet {
-      if isTransitioning {
-        if let progressUpdateObservers = progressUpdateObservers {
-          for observer in progressUpdateObservers {
-            observer.motionDidUpdateProgress(progress: progress)
-          }
+            guard isTransitioning else {
+                return
             }
             
-        let elapsedTime = progress * totalDuration
-        if interactive {
-          for animator in animators {
-            animator.seek(to: elapsedTime)
-          }
-        } else {
-          for plugin in plugins where plugin.requirePerFrameCallback {
-            plugin.seek(to: elapsedTime)
-          }
-        }
+            updateTransitionObservers()
+            
+            guard isInteractive else {
+                updatePlugins()
+                return
             }
+            
+            updateAnimators()
         }
     }
-  /// whether or not we are doing a transition
+    
+    /// A boolean indicating whether a transition is active.
     public var isTransitioning: Bool {
-    return transitionContainer != nil
+        return nil != transitionContainer
     }
 
-  /// container we created to hold all animating views, will be a subview of the
-  /// transitionContainer when isTransitioning
+    /**
+     A view container used to hold all the animating views during a 
+     transition.
+     */
     public internal(set) var container: UIView!
 
-  /// this is the container supplied by UIKit
+    /// UIKit's supplied transition container.
     internal var transitionContainer: UIView!
 
+    /// An optional completion callback.
     internal var completionCallback: ((Bool) -> Void)?
     
+    /// Binds the render cycle to the transition animation.
     internal var displayLink: CADisplayLink?
-  internal var progressUpdateObservers: [MotionProgressUpdateObserver]?
     
-  /// max duration needed by the default animator and plugins
-  public internal(set) var totalDuration: TimeInterval = 0.0
+    /// An Array of observers that are updated during a transition.
+    internal var transitionObservers: [MotionTransitionObserver]?
+
+    /// Max duration used by MotionAnimators and MotionPlugins.
+    public internal(set) var totalDuration: TimeInterval = 0
 
-  /// current animation complete duration.
-  /// (differs from totalDuration because this one could be the duration for finishing interactive transition)
-  internal var duration: TimeInterval = 0.0
+    /// The currently running animation duration.
+    internal var currentAnimationDuration: TimeInterval = 0
+    
+    /// The start time of the animation.
     internal var beginTime: TimeInterval? {
         didSet {
-      if beginTime != nil {
-        if displayLink == nil {
-          displayLink = CADisplayLink(target: self, selector: #selector(displayUpdate(_:)))
-          displayLink!.add(to: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
-        }
-      } else {
+            guard nil != beginTime else {
                 displayLink?.isPaused = true
                 displayLink?.remove(from: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
                 displayLink = nil
+                return
             }
-    }
-  }
-  func displayUpdate(_ link: CADisplayLink) {
-    if isTransitioning, duration > 0, let beginTime = beginTime {
-      let elapsedTime = CACurrentMediaTime() - beginTime
             
-      if elapsedTime > duration {
-        progress = finishing ? 1 : 0
-        self.beginTime = nil
-        complete(finished: finishing)
-      } else {
-        var completed = elapsedTime / totalDuration
-        if !finishing {
-          completed = 1 - completed
-        }
-        completed = max(0, min(1, completed))
-        progress = completed
+            guard nil == displayLink else {
+                return
             }
+            
+            displayLink = CADisplayLink(target: self, selector: #selector(handleDisplayLink(_:)))
+            displayLink?.add(to: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
         }
     }
 
-  internal var finishing: Bool = true
+    /// A boolean indicating if the transition has finished.
+    internal var isFinished = true
 
+    /// An Array of MotionPreprocessors used during a transition.
     internal var processors: [MotionPreprocessor]!
+
+    /// An Array of MotionAnimators used during a transition.
     internal var animators: [MotionAnimator]!
+
+    /// An Array of MotionPlugins used during a transition.
     internal var plugins: [MotionPlugin]!
 
-  internal var animatingViews: [(fromViews: [UIView], toViews: [UIView])]!
+    /// The matching from-views to to-views based on the motionIdentifier value.
+    internal var transitionPairs: [(fromViews: [UIView], toViews: [UIView])]!
 
-  internal static var enabledPlugins: [MotionPlugin.Type] = []
+    /// Plugins that are enabled during the transition.
+    internal static var enabledPlugins = [MotionPlugin.Type]()
 
+    /// Initializer.
     internal override init() {}
 }
 
+fileprivate extension MotionController {
+    /// Updates the transition observers.
+    func updateTransitionObservers() {
+        guard let observers = transitionObservers else {
+            return
+        }
+        
+        for v in observers {
+            v.motion(transitionObserver: v, didUpdateWith: elapsedTime)
+        }
+    }
+    
+    /// Updates the animators.
+    func updateAnimators() {
+        let v = elapsedTime * totalDuration
+        for a in animators {
+            a.seek(to: v)
+        }
+    }
+    
+    /// Updates the plugins.
+    func updatePlugins() {
+        let v = elapsedTime * totalDuration
+        for p in plugins where p.requirePerFrameCallback {
+            p.seek(to: v)
+        }
+    }
+}
+
+fileprivate extension MotionController {
+    @objc
+    func handleDisplayLink(_ link: CADisplayLink) {
+        guard isTransitioning else {
+            return
+        }
+        
+        guard 0 < currentAnimationDuration else {
+            return
+        }
+        
+        guard let t = beginTime else {
+            return
+        }
+        
+        let cTime = CACurrentMediaTime() - t
+        
+        if cTime > currentAnimationDuration {
+            elapsedTime = isFinished ? 1 : 0
+            
+            beginTime = nil
+            
+            complete(isFinished: isFinished)
+        
+        } else {
+            var eTime = cTime / totalDuration
+            
+            if !isFinished {
+                eTime = 1 - eTime
+            }
+            
+            elapsedTime = max(0, min(1, eTime))
+        }
+    }
+}
+
 public extension MotionController {
   // MARK: Interactive Transition
 
@@ -140,7 +201,7 @@ public extension MotionController {
   public func update(progress: Double) {
     guard isTransitioning else { return }
     self.beginTime = nil
-    self.progress = max(-1, min(1, progress))
+    self.elapsedTime = max(-1, min(1, progress))
   }
 
   /**
@@ -151,14 +212,14 @@ public extension MotionController {
   public func end(animate: Bool = true) {
     guard isTransitioning else { return }
     if !animate {
-      self.complete(finished:true)
+      self.complete(isFinished:true)
       return
     }
     var maxTime: TimeInterval = 0
     for animator in self.animators {
-      maxTime = max(maxTime, animator.resume(at: self.progress * self.totalDuration, isReversed: false))
+      maxTime = max(maxTime, animator.resume(at: self.elapsedTime * self.totalDuration, isReversed: false))
     }
-    self.complete(after: maxTime, finishing: true)
+    self.complete(after: maxTime, isFinished: true)
   }
 
   /**
@@ -169,18 +230,18 @@ public extension MotionController {
   public func cancel(animate: Bool = true) {
     guard isTransitioning else { return }
     if !animate {
-      self.complete(finished:false)
+      self.complete(isFinished:false)
       return
     }
     var maxTime: TimeInterval = 0
     for animator in self.animators {
-      var adjustedProgress = self.progress
+      var adjustedProgress = self.elapsedTime
       if adjustedProgress < 0 {
         adjustedProgress = -adjustedProgress
       }
       maxTime = max(maxTime, animator.resume(at: adjustedProgress * self.totalDuration, isReversed: true))
     }
-    self.complete(after: maxTime, finishing: false)
+    self.complete(after: maxTime, isFinished: false)
   }
 
   /**
@@ -219,11 +280,11 @@ public extension MotionController {
    - Parameters:
    - observer: the observer
    */
-  func observeForProgressUpdate(observer: MotionProgressUpdateObserver) {
-    if progressUpdateObservers == nil {
-      progressUpdateObservers = []
+  func observeForProgressUpdate(observer: MotionTransitionObserver) {
+    if transitionObservers == nil {
+      transitionObservers = []
     }
-    progressUpdateObservers!.append(observer)
+    transitionObservers!.append(observer)
   }
 }
 
@@ -283,7 +344,7 @@ internal extension MotionController {
 
   func prepareForAnimation() {
     guard isTransitioning else { fatalError() }
-    animatingViews = [([UIView], [UIView])]()
+    transitionPairs = [([UIView], [UIView])]()
     for animator in animators {
       let currentFromViews = context.fromViews.filter { (view: UIView) -> Bool in
         return animator.canAnimate(view: view, isAppearing: false)
@@ -291,7 +352,7 @@ internal extension MotionController {
       let currentToViews = context.toViews.filter { (view: UIView) -> Bool in
         return animator.canAnimate(view: view, isAppearing: true)
       }
-      animatingViews.append((currentFromViews, currentToViews))
+      transitionPairs.append((currentFromViews, currentToViews))
     }
   }
 
@@ -299,7 +360,7 @@ internal extension MotionController {
   /// subclass should call `prepareForTransition` & `prepareForAnimation` before calling `animate`
   func animate() {
     guard isTransitioning else { fatalError() }
-    for (currentFromViews, currentToViews) in animatingViews {
+    for (currentFromViews, currentToViews) in transitionPairs {
       // auto hide all animated views
       for view in currentFromViews {
         context.hide(view: view)
@@ -312,8 +373,8 @@ internal extension MotionController {
     var totalDuration: TimeInterval = 0
     var animatorWantsInteractive = false
     for (i, animator) in animators.enumerated() {
-      let duration = animator.animate(fromViews: animatingViews[i].0,
-                                      toViews: animatingViews[i].1)
+      let duration = animator.animate(fromViews: transitionPairs[i].0,
+                                      toViews: transitionPairs[i].1)
       if duration == .infinity {
         animatorWantsInteractive = true
       } else {
@@ -325,23 +386,23 @@ internal extension MotionController {
     if animatorWantsInteractive {
       update(progress: 0)
     } else {
-      complete(after: totalDuration, finishing: true)
+      complete(after: totalDuration, isFinished: true)
     }
   }
 
-  func complete(after: TimeInterval, finishing: Bool) {
+  func complete(after: TimeInterval, isFinished: Bool) {
     guard isTransitioning else { fatalError() }
     if after <= 0.001 {
-      complete(finished: finishing)
+      complete(isFinished: isFinished)
       return
     }
-    let elapsedTime = (finishing ? progress : 1 - progress) * totalDuration
-    self.finishing = finishing
-    self.duration = after + elapsedTime
-    self.beginTime = CACurrentMediaTime() - elapsedTime
+    let v = (isFinished ? elapsedTime : 1 - elapsedTime) * totalDuration
+    self.isFinished = isFinished
+    self.currentAnimationDuration = after + v
+    self.beginTime = CACurrentMediaTime() - v
   }
 
-  func complete(finished: Bool) {
+  func complete(isFinished: Bool) {
     guard isTransitioning else { fatalError() }
     for animator in animators {
       animator.clean()
@@ -351,8 +412,8 @@ internal extension MotionController {
 
     let completion = completionCallback
 
-    animatingViews = nil
-    progressUpdateObservers = nil
+    transitionPairs = nil
+    transitionObservers = nil
     transitionContainer = nil
     completionCallback = nil
     container = nil
@@ -361,10 +422,10 @@ internal extension MotionController {
     plugins = nil
     context = nil
     beginTime = nil
-    progress = 0
+    elapsedTime = 0
     totalDuration = 0
 
-    completion?(finished)
+    completion?(isFinished)
   }
 }
 

Sources/MotionTransitionObserver.swift

+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (C) 2017, Daniel Dahan and CosmicMind, Inc. <http://cosmicmind.com>.
+ * All rights reserved.
+ *
+ * Original Inspiration & Author
+ * Copyright (c) 2016 Luke Zhao <me@lkzhao.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+import Foundation
+
+public protocol MotionTransitionObserver {
+    /**
+     Executed when the elapsed time changes during a transition.
+     - Parameter transitionObserver: A MotionTransitionObserver. 
+     - Parameter didUpdateWith elapsedTime: A TimeInterval.
+     */
+    func motion(transitionObserver: MotionTransitionObserver, didUpdateWith elapsedTime: TimeInterval)
+}

Sources/MotionTypes.swift → Sources/MotionViewController.swift

@@ -28,10 +28,6 @@
 
 import UIKit
 
-public protocol MotionProgressUpdateObserver {
-    func motionDidUpdateProgress(progress: Double)
-}
-
 @objc(MotionViewControllerDelegate)
 public protocol MotionViewControllerDelegate {
     @objc