Added parallax effect for cupertino fullscreenDialog (#50180)

packages/flutter/lib/src/cupertino/route.dart

@@ -300,21 +300,24 @@ class CupertinoPageRoute<T> extends PageRoute<T> {
     Animation<double> secondaryAnimation,
     Widget child,
   ) {
+    // Check if the route has an animation that's currently participating
+    // in a back swipe gesture.
+    //
+    // In the middle of a back gesture drag, let the transition be linear to
+    // match finger motions.
+    final bool linearTransition = isPopGestureInProgress(route);
     if (route.fullscreenDialog) {
       return CupertinoFullscreenDialogTransition(
-        animation: animation,
+        primaryRouteAnimation: animation,
+        secondaryRouteAnimation: secondaryAnimation,
         child: child,
+        linearTransition: linearTransition,
       );
     } else {
       return CupertinoPageTransition(
         primaryRouteAnimation: animation,
         secondaryRouteAnimation: secondaryAnimation,
-        // Check if the route has an animation that's currently participating
-        // in a back swipe gesture.
-        //
-        // In the middle of a back gesture drag, let the transition be linear to
-        // match finger motions.
-        linearTransition: isPopGestureInProgress(route),
+        linearTransition: linearTransition,
         child: _CupertinoBackGestureDetector<T>(
           enabledCallback: () => _isPopGestureEnabled<T>(route),
           onStartPopGesture: () => _startPopGesture<T>(route),
@@ -344,7 +347,7 @@ class CupertinoPageTransition extends StatelessWidget {
   ///    when this screen is being pushed.
   ///  * `secondaryRouteAnimation` is a linear route animation from 0.0 to 1.0
   ///    when another screen is being pushed on top of this one.
-  ///  * `linearTransition` is whether to perform primary transition linearly.
+  ///  * `linearTransition` is whether to perform the transitions linearly.
   ///    Used to precisely track back gesture drags.
   CupertinoPageTransition({
     Key key,
@@ -422,29 +425,56 @@ class CupertinoPageTransition extends StatelessWidget {
 /// screen from the bottom.
 class CupertinoFullscreenDialogTransition extends StatelessWidget {
   /// Creates an iOS-style transition used for summoning fullscreen dialogs.
+  ///
+  ///  * `primaryRouteAnimation` is a linear route animation from 0.0 to 1.0
+  ///    when this screen is being pushed.
+  ///  * `secondaryRouteAnimation` is a linear route animation from 0.0 to 1.0
+  ///    when another screen is being pushed on top of this one.
+  ///  * `linearTransition` is whether to perform the secondary transition linearly.
+  ///    Used to precisely track back gesture drags.
   CupertinoFullscreenDialogTransition({
     Key key,
-    @required Animation<double> animation,
+    @required Animation<double> primaryRouteAnimation,
+    @required Animation<double> secondaryRouteAnimation,
     @required this.child,
+    @required bool linearTransition,
   }) : _positionAnimation = CurvedAnimation(
-         parent: animation,
+         parent: primaryRouteAnimation,
          curve: Curves.linearToEaseOut,
          // The curve must be flipped so that the reverse animation doesn't play
          // an ease-in curve, which iOS does not use.
          reverseCurve: Curves.linearToEaseOut.flipped,
        ).drive(_kBottomUpTween),
+       _secondaryPositionAnimation =
+           (linearTransition
+             ? secondaryRouteAnimation
+             : CurvedAnimation(
+                 parent: secondaryRouteAnimation,
+                 curve: Curves.linearToEaseOut,
+                 reverseCurve: Curves.easeInToLinear,
+               )
+           ).drive(_kMiddleLeftTween),
        super(key: key);
 
   final Animation<Offset> _positionAnimation;
+  // When this page is becoming covered by another page.
+  final Animation<Offset> _secondaryPositionAnimation;
 
   /// The widget below this widget in the tree.
   final Widget child;
 
   @override
   Widget build(BuildContext context) {
+    assert(debugCheckHasDirectionality(context));
+    final TextDirection textDirection = Directionality.of(context);
     return SlideTransition(
-      position: _positionAnimation,
-      child: child,
+      position: _secondaryPositionAnimation,
+      textDirection: textDirection,
+      transformHitTests: false,
+      child: SlideTransition(
+        position: _positionAnimation,
+        child: child,
+      ),
     );
   }
 }

packages/flutter/test/cupertino/route_test.dart

@@ -502,6 +502,184 @@ void main() {
     expect(tester.getTopLeft(find.byType(Placeholder)).dy, closeTo(600.0, 0.1));
   });
 
+  Future<void> testParallax(WidgetTester tester, {@required bool fromFullscreenDialog}) async {
+    await tester.pumpWidget(
+      CupertinoApp(
+        onGenerateRoute: (RouteSettings settings) => CupertinoPageRoute<void>(
+          fullscreenDialog: fromFullscreenDialog,
+          settings: settings,
+          builder: (BuildContext context) {
+            return Column(
+              children: <Widget>[
+                const Placeholder(),
+                CupertinoButton(
+                  child: const Text('Button'),
+                  onPressed: () {
+                    Navigator.push<void>(context, CupertinoPageRoute<void>(
+                      builder: (BuildContext context) {
+                        return CupertinoButton(
+                          child: const Text('Close'),
+                          onPressed: () {
+                            Navigator.pop<void>(context);
+                          },
+                        );
+                      },
+                    ));
+                  },
+                ),
+              ],
+            );
+          }
+        ),
+      ),
+    );
+
+    // Enter animation.
+    await tester.tap(find.text('Button'));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(0.0, 0.1));
+    await tester.pump();
+
+    // We use a higher number of intervals since the animation has to scale the
+    // entire screen.
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-70.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-137.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-192.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-227.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-246.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-255.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-260.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-264.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-266.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-267.0, 1.0));
+
+    // Exit animation
+    await tester.tap(find.text('Button'));
+    await tester.pump();
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-198.0, 1.0));
+
+    await tester.pump(const Duration(milliseconds: 360));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(-0.0, 1.0));
+  }
+
+  testWidgets('CupertinoPageRoute has parallax when non fullscreenDialog route is pushed on top', (WidgetTester tester) async {
+    await testParallax(tester, fromFullscreenDialog: false);
+  });
+
+  testWidgets('FullscreenDialog CupertinoPageRoute has parallax when non fullscreenDialog route is pushed on top', (WidgetTester tester) async {
+    await testParallax(tester, fromFullscreenDialog: true);
+  });
+
+  Future<void> testNoParallax(WidgetTester tester, {@required bool fromFullscreenDialog}) async{
+    await tester.pumpWidget(
+      CupertinoApp(
+        onGenerateRoute: (RouteSettings settings) => CupertinoPageRoute<void>(
+          fullscreenDialog: fromFullscreenDialog,
+          builder: (BuildContext context) {
+            return Column(
+              children: <Widget>[
+                const Placeholder(),
+                CupertinoButton(
+                  child: const Text('Button'),
+                  onPressed: () {
+                    Navigator.push<void>(context, CupertinoPageRoute<void>(
+                      fullscreenDialog: true,
+                      builder: (BuildContext context) {
+                        return CupertinoButton(
+                          child: const Text('Close'),
+                          onPressed: () {
+                            Navigator.pop<void>(context);
+                          },
+                        );
+                      },
+                    ));
+                  },
+                ),
+              ],
+            );
+          }
+        ),
+      ),
+    );
+
+    // Enter animation.
+    await tester.tap(find.text('Button'));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, closeTo(0.0, 0.1));
+    await tester.pump();
+
+    // We use a higher number of intervals since the animation has to scale the
+    // entire screen.
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    // Exit animation
+    await tester.tap(find.text('Button'));
+    await tester.pump();
+
+    await tester.pump(const Duration(milliseconds: 40));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+
+    await tester.pump(const Duration(milliseconds: 360));
+    expect(tester.getTopLeft(find.byType(Placeholder)).dx, 0.0);
+  }
+
+  testWidgets('CupertinoPageRoute has no parallax when fullscreenDialog route is pushed on top', (WidgetTester tester) async {
+    await testNoParallax(tester, fromFullscreenDialog: false);
+  });
+
+  testWidgets('FullscreenDialog CupertinoPageRoute has no parallax when fullscreenDialog route is pushed on top', (WidgetTester tester) async {
+    await testNoParallax(tester, fromFullscreenDialog: true);
+  });
+
   testWidgets('Animated push/pop is not linear', (WidgetTester tester) async {
     await tester.pumpWidget(
       const CupertinoApp(