CupertinoPicker part 1 - create a generic ListWheelScrollView (#13783)

* Create ListWheelScrollView

* fix missing doc

* tweak docs a bit

* fix imports

* Add some tests

* review

* review and transform tests

* fix test

* repatch lost https://github.com/flutter/flutter/commit/977701cf695ec106a52dde9f3659a7b132826748

* review

* Review

packages/flutter/lib/rendering.dart

@@ -44,6 +44,7 @@ export 'src/rendering/flow.dart';
 export 'src/rendering/image.dart';
 export 'src/rendering/layer.dart';
 export 'src/rendering/list_body.dart';
+export 'src/rendering/list_wheel_viewport.dart';
 export 'src/rendering/object.dart';
 export 'src/rendering/paragraph.dart';
 export 'src/rendering/performance_overlay.dart';

packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+
+import 'framework.dart';
+import 'scroll_controller.dart';
+import 'scroll_physics.dart';
+import 'scrollable.dart';
+
+/// A box in which children on a wheel can be scrolled.
+///
+/// This widget is similar to a [ListView] but with the restriction that all
+/// children must be the same size along the scrolling axis.
+///
+/// When the list is at the zero scroll offset, the first child is aligned with
+/// the middle of the viewport. When the list is at the final scroll offset,
+/// the last child is aligned with the middle of the viewport
+///
+/// The children are rendered as if rotating on a wheel instead of scrolling on
+/// a plane.
+class ListWheelScrollView extends StatelessWidget {
+  /// Creates a box in which children are scrolled on a wheel.
+  const ListWheelScrollView({
+    Key key,
+    this.controller,
+    this.physics,
+    this.diameterRatio: RenderListWheelViewport.defaultDiameterRatio,
+    this.perspective: RenderListWheelViewport.defaultPerspective,
+    @required this.itemExtent,
+    this.clipToSize: true,
+    this.renderChildrenOutsideViewport: false,
+    @required this.children,
+  }) : assert(diameterRatio != null),
+       assert(diameterRatio > 0.0, RenderListWheelViewport.diameterRatioZeroMessage),
+       assert(perspective != null),
+       assert(perspective > 0),
+       assert(perspective <= 0.01, RenderListWheelViewport.perspectiveTooHighMessage),
+       assert(itemExtent != null),
+       assert(itemExtent > 0),
+       assert(clipToSize != null),
+       assert(renderChildrenOutsideViewport != null),
+       assert(
+         !renderChildrenOutsideViewport || !clipToSize,
+         RenderListWheelViewport.clipToSizeAndRenderChildrenOutsideViewportConflict,
+       ),
+       super(key: key);
+
+  /// An object that can be used to control the position to which this scroll
+  /// view is scrolled.
+  ///
+  /// A [ScrollController] serves several purposes. It can be used to control
+  /// the initial scroll position (see [ScrollController.initialScrollOffset]).
+  /// It can be used to control whether the scroll view should automatically
+  /// save and restore its scroll position in the [PageStorage] (see
+  /// [ScrollController.keepScrollOffset]). It can be used to read the current
+  /// scroll position (see [ScrollController.offset]), or change it (see
+  /// [ScrollController.animateTo]).
+  final ScrollController controller;
+
+  /// How the scroll view should respond to user input.
+  ///
+  /// For example, determines how the scroll view continues to animate after the
+  /// user stops dragging the scroll view.
+  ///
+  /// Defaults to matching platform conventions.
+  final ScrollPhysics physics;
+
+  /// {@macro flutter.rendering.wheelList.diameterRatio}
+  final double diameterRatio;
+
+  /// {@macro flutter.rendering.wheelList.perspective}
+  final double perspective;
+
+  /// Size of each child in the main axis. Must not be null and must be
+  /// positive.
+  final double itemExtent;
+
+  /// {@macro flutter.rendering.wheelList.clipToSize}
+  final bool clipToSize;
+
+  /// {@macro flutter.rendering.wheelList.renderChildrenOutsideViewport}
+  final bool renderChildrenOutsideViewport;
+
+  /// List of children to scroll on top of the cylinder.
+  final List<Widget> children;
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scrollable(
+      controller: controller,
+      physics: physics,
+      viewportBuilder: (BuildContext context, ViewportOffset offset) {
+        return new ListWheelViewport(
+          diameterRatio: diameterRatio,
+          perspective: perspective,
+          itemExtent: itemExtent,
+          clipToSize: clipToSize,
+          renderChildrenOutsideViewport: renderChildrenOutsideViewport,
+          offset: offset,
+          children: children,
+        );
+      },
+    );
+  }
+}
+
+/// A viewport showing a subset of children on a wheel.
+///
+/// Typically used with [ListWheelScrollView], this viewport is similar to
+/// [Viewport] in that it shows a subset of children in a scrollable based
+/// on the scrolling offset and the childrens' dimensions. But uses
+/// [RenderListWheelViewport] to display the children on a wheel.
+///
+/// See also:
+///
+///  * [ListWheelScrollView], widget that combines this viewport with a scrollable.
+///  * [RenderListWheelViewport], the render object that renders the children
+///    on a wheel.
+class ListWheelViewport extends MultiChildRenderObjectWidget {
+  ListWheelViewport({
+    Key key,
+    this.diameterRatio: RenderListWheelViewport.defaultDiameterRatio,
+    this.perspective: RenderListWheelViewport.defaultPerspective,
+    @required this.itemExtent,
+    this.clipToSize: true,
+    this.renderChildrenOutsideViewport: false,
+    @required this.offset,
+    List<Widget> children,
+  }) : assert(offset != null),
+       assert(diameterRatio != null),
+       assert(diameterRatio > 0, RenderListWheelViewport.diameterRatioZeroMessage),
+       assert(perspective != null),
+       assert(perspective > 0),
+       assert(perspective <= 0.01, RenderListWheelViewport.perspectiveTooHighMessage),
+       assert(itemExtent != null),
+       assert(itemExtent > 0),
+       assert(clipToSize != null),
+       assert(renderChildrenOutsideViewport != null),
+       assert(
+         !renderChildrenOutsideViewport || !clipToSize,
+         RenderListWheelViewport.clipToSizeAndRenderChildrenOutsideViewportConflict,
+       ),
+       super(key: key, children: children);
+
+  /// {@macro flutter.rendering.wheelList.diameterRatio}
+  final double diameterRatio;
+
+  /// {@macro flutter.rendering.wheelList.perspective}
+  final double perspective;
+
+  /// {@macro flutter.rendering.wheelList.itemExtent}
+  final double itemExtent;
+
+  /// {@macro flutter.rendering.wheelList.clipToSize}
+  final bool clipToSize;
+
+  /// {@macro flutter.rendering.wheelList.renderChildrenOutsideViewport}
+  final bool renderChildrenOutsideViewport;
+
+  /// [ViewportOffset] object describing the content that should be visible
+  /// in the viewport.
+  final ViewportOffset offset;
+
+  @override
+  RenderListWheelViewport createRenderObject(BuildContext context) {
+    return new RenderListWheelViewport(
+      diameterRatio: diameterRatio,
+      perspective: perspective,
+      itemExtent: itemExtent,
+      clipToSize: clipToSize,
+      renderChildrenOutsideViewport: renderChildrenOutsideViewport,
+      offset: offset,
+    );
+  }
+
+  @override
+  void updateRenderObject(BuildContext context, RenderListWheelViewport renderObject) {
+    renderObject
+      ..diameterRatio = diameterRatio
+      ..perspective = perspective
+      ..itemExtent = itemExtent
+      ..clipToSize = clipToSize
+      ..renderChildrenOutsideViewport = renderChildrenOutsideViewport
+      ..offset = offset;
+  }
+}

packages/flutter/lib/widgets.dart

@@ -45,6 +45,7 @@ export 'src/widgets/image.dart';
 export 'src/widgets/image_icon.dart';
 export 'src/widgets/implicit_animations.dart';
 export 'src/widgets/layout_builder.dart';
+export 'src/widgets/list_wheel_scroll_view.dart';
 export 'src/widgets/localizations.dart';
 export 'src/widgets/media_query.dart';
 export 'src/widgets/modal_barrier.dart';

packages/flutter/test/rendering/mock_canvas.dart

@@ -74,6 +74,21 @@ typedef void _CanvasPainterFunction(Canvas canvas);
 /// Patterns are subset matches, meaning that any calls not described by the
 /// pattern are ignored. This allows, for instance, transforms to be skipped.
 abstract class PaintPattern {
+  /// Indicates that a transform is expected next.
+  ///
+  /// Calls are skipped until a call to [Canvas.transform] is found. The call's
+  /// arguments are compared to those provided here. If any fail to match, or if
+  /// no call to [Canvas.transform] is found, then the matcher fails.
+  ///
+  /// Dynamic so matchers can be more easily passed in.
+  ///
+  /// The `matrix4` argument is dynamic so it can be either a [Matcher], or a
+  /// [Float64List] of [double]s. If it is a [Float64List] of [double]s then
+  /// each value in the matrix must match in the expected matrix. A deep
+  /// matching [Matcher] such as [equals] can be used to test each value in the
+  /// matrix with utilities such as [moreOrLessEquals].
+  void transform({ dynamic matrix4 });
+
   /// Indicates that a translation transform is expected next.
   ///
   /// Calls are skipped until a call to [Canvas.translate] is found. The call's
@@ -574,6 +589,11 @@ class _TestRecordingCanvasPaintsAssertionMatcher extends Matcher {
 class _TestRecordingCanvasPatternMatcher extends _TestRecordingCanvasMatcher implements PaintPattern {
   final List<_PaintPredicate> _predicates = <_PaintPredicate>[];
 
+  @override
+  void transform({ dynamic matrix4 }) {
+    _predicates.add(new _FunctionPaintPredicate(#transform, <dynamic>[matrix4]));
+  }
+
   @override
   void translate({ double x, double y }) {
     _predicates.add(new _FunctionPaintPredicate(#translate, <dynamic>[x, y]));

packages/flutter/test/rendering/recording_canvas.dart

@@ -110,6 +110,14 @@ class TestRecordingPaintingContext implements PaintingContext {
     canvas.restore();
   }
 
+  @override
+  void pushTransform(bool needsCompositing, Offset offset, Matrix4 transform, PaintingContextCallback painter) {
+    canvas.save();
+    canvas.transform(transform.storage);
+    painter(this, offset);
+    canvas.restore();
+  }
+
   @override
   void noSuchMethod(Invocation invocation) { }
 }