Operators that use _map no longer transform velocity by default.

Summary: Velocity transformation is now opt in. Only x() and y() opt in to this behavior.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, #material_motion, markwei

Reviewed By: O2 Material Motion, O4 Material Apple platform reviewers, #material_motion, markwei

Tags: #material_motion

Differential Revision: http://codereview.cc/D3078

src/operators/foundation/_map.swift

@@ -24,7 +24,7 @@ extension MotionObservableConvertible {
 
    This operator is meant to be used when building other operators.
    */
-  public func _map<U>(_ name: String? = nil, args: [Any]? = nil, transform: @escaping (T) -> U) -> MotionObservable<U> {
+  public func _map<U>(_ name: String? = nil, args: [Any]? = nil, transformVelocity: Bool = false, transform: @escaping (T) -> U) -> MotionObservable<U> {
     return _nextOperator(name, args: args, operation: { value, next in
       next(transform(value))
 
@@ -33,7 +33,7 @@ extension MotionObservableConvertible {
       switch event {
       case .add(let info):
         if let initialVelocity = info.initialVelocity {
-          transformedInitialVelocity = transform(initialVelocity as! T)
+          transformedInitialVelocity = transformVelocity ? transform(initialVelocity as! T) : initialVelocity
         } else {
           transformedInitialVelocity = nil
         }

src/operators/x.swift

@@ -23,7 +23,7 @@ extension MotionObservableConvertible where T == CGPoint {
    Extract the x value from a CGPoint.
    */
   public func x() -> MotionObservable<CGFloat> {
-    return _map(#function) {
+    return _map(#function, transformVelocity: true) {
       $0.x
     }
   }

src/operators/y.swift

@@ -23,7 +23,7 @@ extension MotionObservableConvertible where T == CGPoint {
    Extract the y value from a CGPoint.
    */
   public func y() -> MotionObservable<CGFloat> {
-    return _map(#function) {
+    return _map(#function, transformVelocity: true) {
       $0.y
     }
   }

tests/unit/operator/foundation/_mapTests.swift

@@ -121,7 +121,7 @@ class _mapTests: XCTestCase {
     }
 
     let eventReceived = expectation(description: "Event was received")
-    let _ = observable._map { value in
+    let _ = observable._map(transformVelocity: true) { value in
       return value * scalar
 
       }.subscribe(next: { _ in }, coreAnimation: { event in