initial pass at MotionController rework

fcf3d822 · Daniel Dahan · 19664a2f · fcf3d822 · fcf3d822 · fcf3d822
Commit fcf3d822 authored Jun 08, 2017 by Daniel Dahan
Showing with 379 additions and 244 deletions

Motion.xcodeproj/project.pbxproj
+8 -4

Sources/Motion.swift
+161 -125

Sources/MotionController.swift
+172 -111

Sources/MotionTransitionObserver.swift
+38 -0

Sources/MotionViewController.swift
+0 -4

No files found.
--- a/Motion.xcodeproj/project.pbxproj
+++ b/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 */,

--- a/Sources/Motion.swift
+++ b/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 {
+            guard isTransitioning else {
-                transitionContext?.updateInteractiveTransition(CGFloat(progress))
+                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()
+        processForAnimation()
-        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
    }
+}
+internal extension Motion {
    override func animate() {
        context.unhide(view: toView)
-        if let containerBackgroundColor = containerBackgroundColor {
+        updateContainerBackgroundColor()
-            container.backgroundColor = containerBackgroundColor
+        updateInsertOrder()
-        } 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
-            }
-        }
        super.animate()
-        fullScreenSnapshot!.removeFromSuperview()
+        fullScreenSnapshot?.removeFromSuperview()
    }
    override func complete(finished: Bool) {
@@ -218,13 +194,13 @@ internal extension Motion {
        }
        context.clean()
        if finished && isPresenting && toOverFullScreen {
            // finished presenting a overFullScreen VC
            context.unhide(rootView: toView)
            context.removeSnapshots(rootView: toView)
            context.storeViewAlpha(rootView: fromView)
            fromViewController!.motionStoredSnapshot = container
            fromView.removeFromSuperview()
            fromView.addSubview(container)
@@ -262,7 +238,7 @@ internal extension Motion {
        let tContext = transitionContext
        let fvc = fromViewController
        let tvc = toViewController
        transitionContext = nil
        fromViewController = nil
        toViewController = nil
@@ -274,7 +250,7 @@ internal extension Motion {
        defaultAnimation = .auto
        super.complete(finished: finished)
        if finished {
            if let fvc = fvc, let tvc = tvc {
                processForMotionDelegate(viewController: fvc) {
@@ -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 {
@@ -418,99 +440,113 @@ internal extension Motion {
    }
 }
-// MARK: UIKit Protocol Conformance
-/*****************************
- * UIKit protocol extensions *
- *****************************/
 extension Motion: UIViewControllerAnimatedTransitioning {
-  public func animateTransition(using context: UIViewControllerContextTransitioning) {
+    /**
-    guard !isTransitioning else { return }
+     The animation method that is used to coordinate the transition.
-    transitionContext = context
+     - Parameter using transitionContext: A UIViewControllerContextTransitioning.
-    fromViewController = fromViewController ?? context.viewController(forKey: .from)
+     */
-    toViewController = toViewController ?? context.viewController(forKey: .to)
+    public func animateTransition(using context: UIViewControllerContextTransitioning) {
-    transitionContainer = context.containerView
+        guard !isTransitioning else {
-    start()
+            return
-  }
+        }
-  public func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
-    return 0.375 // doesn't matter, real duration will be calculated later
+        transitionContext = context
-  }
+        fromViewController = fromViewController ?? context.viewController(forKey: .from)
+        toViewController = toViewController ?? context.viewController(forKey: .to)
-  public func animationEnded(_ transitionCompleted: Bool) {
+        transitionContainer = context.containerView
-    isAnimating = !transitionCompleted
-  }
+        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 // Will be updated dynamically.
+    }
+    public func animationEnded(_ transitionCompleted: Bool) {
+        isAnimating = !transitionCompleted
+    }
 }
-extension Motion:UIViewControllerTransitioningDelegate {
+extension Motion {
-  var interactiveTransitioning: UIViewControllerInteractiveTransitioning? {
+    /// A reference to the interactive transitioning.
-    return forceNonInteractive ? nil : self
+    fileprivate var interactiveTransitioning: UIViewControllerInteractiveTransitioning? {
-  }
+        return self
+    }
-  public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+}
-    self.isPresenting = true
-    self.fromViewController = fromViewController ?? presenting
+extension Motion: UIViewControllerTransitioningDelegate {
-    self.toViewController = toViewController ?? presented
+    public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
-    return self
+        self.isPresenting = true
-  }
+        self.fromViewController = fromViewController ?? presenting
+        self.toViewController = toViewController ?? presented
-  public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+        return self
-    self.isPresenting = false
+    }
-    self.fromViewController = fromViewController ?? dismissed
-    return self
+    public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
-  }
+        self.isPresenting = false
+        self.fromViewController = fromViewController ?? dismissed
-  public func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+        return self
-    return interactiveTransitioning
+    }
-  }
+    public func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
-  public func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+        return interactiveTransitioning
-    return interactiveTransitioning
+    }
-  }
+    public func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+        return interactiveTransitioning
+    }
 }
 extension Motion: UIViewControllerInteractiveTransitioning {
-  public var wantsInteractiveStart: Bool {
+    public var wantsInteractiveStart: Bool {
-    return true
+        return true
-  }
+    }
-  public func startInteractiveTransition(_ transitionContext: UIViewControllerContextTransitioning) {
+    public func startInteractiveTransition(_ transitionContext: UIViewControllerContextTransitioning) {
-    animateTransition(using: transitionContext)
+        animateTransition(using: transitionContext)
-  }
+    }
 }
 extension Motion: UINavigationControllerDelegate {
-  public func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+    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.fromViewController = fromViewController ?? fromVC
-    self.toViewController = toViewController ?? toVC
+        self.toViewController = toViewController ?? toVC
-    self.isNavigationController = true
+        self.isNavigationController = true
-    return self
+        return self
-  }
+    }
-  public func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+    public func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
-    return interactiveTransitioning
+        return interactiveTransitioning
-  }
+    }
 }
 extension Motion: UITabBarControllerDelegate {
-  public func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
+    public func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
-    return !isAnimating
+        return !isAnimating
-  }
+    }
-  public func tabBarController(_ tabBarController: UITabBarController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+    public func tabBarController(_ tabBarController: UITabBarController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
-    return interactiveTransitioning
+        return interactiveTransitioning
-  }
+    }
-  public func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+    public func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
-    isAnimating = true
+        isAnimating = true
-    let fromVCIndex = tabBarController.childViewControllers.index(of: fromVC)!
-    let toVCIndex = tabBarController.childViewControllers.index(of: toVC)!
+        let fromVCIndex = tabBarController.childViewControllers.index(of: fromVC)!
-    self.isPresenting = toVCIndex > fromVCIndex
+        let toVCIndex = tabBarController.childViewControllers.index(of: toVC)!
-    self.fromViewController = fromViewController ?? fromVC
-    self.toViewController = toViewController ?? toVC
+        self.isPresenting = toVCIndex > fromVCIndex
-    self.isTabBarController = true
+        self.fromViewController = fromViewController ?? fromVC
-    return self
+        self.toViewController = toViewController ?? toVC
-  }
+        self.isTabBarController = true
+        return self
+    }
 }
 public typealias MotionDelayCancelBlock = (Bool) -> Void

--- a/Sources/MotionController.swift
+++ b/Sources/MotionController.swift
@@ -28,105 +28,166 @@
 import UIKit
-/// Base class for managing a Motion transition
 public class MotionController: NSObject {
-  // MARK: Properties
+    /// A reference to the MotionContext.
-  /// context object holding transition informations
+    public internal(set) var context: MotionContext!
-  public internal(set) var context: MotionContext!
-  /// whether or not we are handling transition interactively
-  public var interactive: Bool {
-    return displayLink == nil
-  }
-  /// progress of the current transition. 0 if no transition is happening
-  public internal(set) var progress: Double = 0 {
-    didSet {
-      if isTransitioning {
-        if let progressUpdateObservers = progressUpdateObservers {
-          for observer in progressUpdateObservers {
-            observer.motionDidUpdateProgress(progress: progress)
-          }
-        }
-        let elapsedTime = progress * totalDuration
+    /// A boolean indicating whether the transition interactive or not.
-        if interactive {
+    public var isInteractive: Bool {
-          for animator in animators {
+        return nil == displayLink
-            animator.seek(to: elapsedTime)
+    }
-          }
-        } else {
+    /// Progress of the current transition. 0 if no transition is happening.
-          for plugin in plugins where plugin.requirePerFrameCallback {
+    public internal(set) var elapsedTime: TimeInterval = 0 {
-            plugin.seek(to: elapsedTime)
+        didSet {
-          }
+            guard isTransitioning else {
+                return
+            }
+            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 {
+    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
-  public internal(set) var container: UIView!
-  /// this is the container supplied by UIKit
+    /**
-  internal var transitionContainer: UIView!
+     A view container used to hold all the animating views during a 
+     transition.
+     */
+    public internal(set) var container: UIView!
-  internal var completionCallback: ((Bool) -> Void)?
+    /// UIKit's supplied transition container.
+    internal var transitionContainer: UIView!
-  internal var displayLink: CADisplayLink?
+    /// An optional completion callback.
-  internal var progressUpdateObservers: [MotionProgressUpdateObserver]?
+    internal var completionCallback: ((Bool) -> Void)?
+    /// Binds the render cycle to the transition animation.
+    internal var displayLink: CADisplayLink?
+    /// An Array of observers that are updated during a transition.
+    internal var transitionObservers: [MotionTransitionObserver]?
-  /// max duration needed by the default animator and plugins
+    /// Max duration used by MotionAnimators and MotionPlugins.
-  public internal(set) var totalDuration: TimeInterval = 0.0
+    public internal(set) var totalDuration: TimeInterval = 0
-  /// current animation complete duration.
+    /// The currently running animation duration.
-  /// (differs from totalDuration because this one could be the duration for finishing interactive transition)
+    internal var currentAnimationDuration: TimeInterval = 0
-  internal var duration: TimeInterval = 0.0
-  internal var beginTime: TimeInterval? {
+    /// The start time of the animation.
-    didSet {
+    internal var beginTime: TimeInterval? {
-      if beginTime != nil {
+        didSet {
-        if displayLink == nil {
+            guard nil != beginTime else {
-          displayLink = CADisplayLink(target: self, selector: #selector(displayUpdate(_:)))
+                displayLink?.isPaused = true
-          displayLink!.add(to: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
+                displayLink?.remove(from: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
-        }
+                displayLink = nil
-      } else {
+                return
-        displayLink?.isPaused = true
+            }
-        displayLink?.remove(from: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
-        displayLink = nil
+            guard nil == displayLink else {
-      }
+                return
-    }
+            }
-  }
-  func displayUpdate(_ link: CADisplayLink) {
+            displayLink = CADisplayLink(target: self, selector: #selector(handleDisplayLink(_:)))
-    if isTransitioning, duration > 0, let beginTime = beginTime {
+            displayLink?.add(to: RunLoop.main, forMode: RunLoopMode(rawValue: RunLoopMode.commonModes.rawValue))
-      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
-      }
    }
-  }
-  internal var finishing: Bool = true
+    /// A boolean indicating if the transition has finished.
+    internal var isFinished = true
-  internal var processors: [MotionPreprocessor]!
+    /// An Array of MotionPreprocessors used during a transition.
-  internal var animators: [MotionAnimator]!
+    internal var processors: [MotionPreprocessor]!
-  internal var plugins: [MotionPlugin]!
-  internal var animatingViews: [(fromViews: [UIView], toViews: [UIView])]!
+    /// An Array of MotionAnimators used during a transition.
+    internal var animators: [MotionAnimator]!
-  internal static var enabledPlugins: [MotionPlugin.Type] = []
+    /// An Array of MotionPlugins used during a transition.
+    internal var plugins: [MotionPlugin]!
-  internal override init() {}
+    /// The matching from-views to to-views based on the motionIdentifier value.
+    internal var transitionPairs: [(fromViews: [UIView], toViews: [UIView])]!
+    /// 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 {
@@ -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) {
+  func observeForProgressUpdate(observer: MotionTransitionObserver) {
-    if progressUpdateObservers == nil {
+    if transitionObservers == nil {
-      progressUpdateObservers = []
+      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,
+      let duration = animator.animate(fromViews: transitionPairs[i].0,
-                                      toViews: animatingViews[i].1)
+                                      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
+    let v = (isFinished ? elapsedTime : 1 - elapsedTime) * totalDuration
-    self.finishing = finishing
+    self.isFinished = isFinished
-    self.duration = after + elapsedTime
+    self.currentAnimationDuration = after + v
-    self.beginTime = CACurrentMediaTime() - elapsedTime
+    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
+    transitionPairs = nil
-    progressUpdateObservers = 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)
  }
 }

--- a/Sources/MotionTransitionObserver.swift
+++ b/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)
+}
--- a/Sources/MotionTypes.swift
+++ b/Sources/MotionTypes.swift
@@ -28,10 +28,6 @@
 import UIKit
-public protocol MotionProgressUpdateObserver {
-    func motionDidUpdateProgress(progress: Double)
-}
 @objc(MotionViewControllerDelegate)
 public protocol MotionViewControllerDelegate {
    @objc