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This change enables Flutter to generate multiple Scenes to be rendered into separate FlutterViews from a single widget tree. Each Scene is described by a separate render tree, which are all associated with the single widget tree. This PR implements the framework-side mechanisms to describe the content to be rendered into multiple views. Separate engine-side changes are necessary to provide these views to the framework and to draw the framework-generated Scene into them. ## Summary of changes The details of this change are described in [flutter.dev/go/multiple-views](https://flutter.dev/go/multiple-views). Below is a high-level summary organized by layers. ### Rendering layer changes * The `RendererBinding` no longer owns a single `renderView`. In fact, it doesn't OWN any `RenderView`s at all anymore. Instead, it offers an API (`addRenderView`/`removeRenderView`) to add and remove `RenderView`s that then will be MANAGED by the binding. The `RenderView` itself is now owned by a higher-level abstraction (e.g. the `RawView` Element of the widgets layer, see below), who is also in charge of adding it to the binding. When added, the binding will interact with the `RenderView` to produce a frame (e.g. by calling `compositeFrame` on it) and to perform hit tests for incoming pointer events. Multiple `RenderView`s can be added to the binding (typically one per `FlutterView`) to produce multiple Scenes. * Instead of owning a single `pipelineOwner`, the `RendererBinding` now owns the root of the `PipelineOwner` tree (exposed as `rootPipelineOwner` on the binding). Each `PipelineOwner` in that tree (except for the root) typically manages its own render tree typically rooted in one of the `RenderView`s mentioned in the previous bullet. During frame production, the binding will instruct each `PipelineOwner` of that tree to flush layout, paint, semantics etc. A higher-level abstraction (e.g. the widgets layer, see below) is in charge of adding `PipelineOwner`s to this tree. * Backwards compatibility: The old `renderView` and `pipelineOwner` properties of the `RendererBinding` are retained, but marked as deprecated. Care has been taken to keep their original behavior for the deprecation period, i.e. if you just call `runApp`, the render tree bootstrapped by this call is rooted in the deprecated `RendererBinding.renderView` and managed by the deprecated `RendererBinding.pipelineOwner`. ### Widgets layer changes * The `WidgetsBinding` no longer attaches the widget tree to an existing render tree. Instead, it bootstraps a stand-alone widget tree that is not backed by a render tree. For this, `RenderObjectToWidgetAdapter` has been replaced by `RootWidget`. * Multiple render trees can be bootstrapped and attached to the widget tree with the help of the `View` widget, which internally is backed by a `RawView` widget. Configured with a `FlutterView` to render into, the `RawView` creates a new `PipelineOwner` and a new `RenderView` for the new render tree. It adds the new `RenderView` to the `RendererBinding` and its `PipelineOwner` to the pipeline owner tree. * The `View` widget can only appear in certain well-defined locations in the widget tree since it bootstraps a new render tree and does not insert a `RenderObject` into an ancestor. However, almost all Elements expect that their children insert `RenderObject`s, otherwise they will not function properly. To produce a good error message when the `View` widget is used in an illegal location, the `debugMustInsertRenderObjectIntoSlot` method has been added to Element, where a child can ask whether a given slot must insert a RenderObject into its ancestor or not. In practice, the `View` widget can be used as a child of the `RootWidget`, inside the `view` slot of the `ViewAnchor` (see below) and inside a `ViewCollection` (see below). In those locations, the `View` widget may be wrapped in other non-RenderObjectWidgets (e.g. InheritedWidgets). * The new `ViewAnchor` can be used to create a side-view inside a parent `View`. The `child` of the `ViewAnchor` widget renders into the parent `View` as usual, but the `view` slot can take on another `View` widget, which has access to all inherited widgets above the `ViewAnchor`. Metaphorically speaking, the view is anchored to the location of the `ViewAnchor` in the widget tree. * The new `ViewCollection` widget allows for multiple sibling views as it takes a list of `View`s as children. It can be used in all the places that accept a `View` widget. ## Google3 As of July 5, 2023 this change passed a TAP global presubmit (TGP) in google3: tap/OCL:544707016:BASE:545809771:1688597935864:e43dd651 ## Note to reviewers This change is big (sorry). I suggest focusing the initial review on the changes inside of `packages/flutter` first. The majority of the changes describe above are implemented in (listed in suggested review order): * `rendering/binding.dart` * `widgets/binding.dart` * `widgets/view.dart` * `widgets/framework.dart` All other changes included in the PR are basically the fallout of what's implemented in those files. Also note that a lot of the lines added in this PR are documentation and tests. I am also very happy to walk reviewers through the code in person or via video call, if that is helpful. I appreciate any feedback. ## Feedback to address before submitting ("TODO")
75 lines
2.3 KiB
Dart
75 lines
2.3 KiB
Dart
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/widgets.dart';
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import 'package:flutter_test/flutter_test.dart';
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class TestBinding extends LiveTestWidgetsFlutterBinding {
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TestBinding();
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int framesBegun = 0;
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int framesDrawn = 0;
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late bool handleBeginFrameMicrotaskRun;
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@override
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void handleBeginFrame(Duration? rawTimeStamp) {
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handleBeginFrameMicrotaskRun = false;
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framesBegun += 1;
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Future<void>.microtask(() { handleBeginFrameMicrotaskRun = true; });
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super.handleBeginFrame(rawTimeStamp);
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}
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@override
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void handleDrawFrame() {
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if (!handleBeginFrameMicrotaskRun) {
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throw "Microtasks scheduled by 'handledBeginFrame' must be run before 'handleDrawFrame'.";
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}
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framesDrawn += 1;
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super.handleDrawFrame();
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}
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}
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void main() {
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late TestBinding binding;
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setUp(() {
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binding = TestBinding();
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});
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test('test pumpBenchmark() only runs one frame', () async {
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await benchmarkWidgets(
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(WidgetTester tester) async {
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const Key root = Key('root');
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binding.attachRootWidget(binding.wrapWithDefaultView(Container(key: root)));
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await tester.pump();
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expect(binding.framesBegun, greaterThan(0));
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expect(binding.framesDrawn, greaterThan(0));
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final Element appState = tester.element(find.byKey(root));
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binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.benchmark;
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final int startFramesBegun = binding.framesBegun;
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final int startFramesDrawn = binding.framesDrawn;
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expect(startFramesBegun, equals(startFramesDrawn));
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appState.markNeedsBuild();
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await tester.pumpBenchmark(const Duration(milliseconds: 16));
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final int endFramesBegun = binding.framesBegun;
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final int endFramesDrawn = binding.framesDrawn;
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expect(endFramesBegun, equals(endFramesDrawn));
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expect(endFramesBegun, equals(startFramesBegun + 1));
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expect(endFramesDrawn, equals(startFramesDrawn + 1));
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},
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// We are not interested in the performance of the "benchmark", we are just
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// testing the behavior. So it's OK that asserts are enabled.
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mayRunWithAsserts: true,
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);
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}, skip: isBrowser); // https://github.com/flutter/flutter/issues/87871
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}
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