6f09064e78
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")
70 lines
2.3 KiB
Dart
70 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 'dart:ui';
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import 'package:flutter/rendering.dart';
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/// An extension of [RenderingFlutterBinding] that owns and manages a
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/// [renderView].
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///
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/// Unlike [RenderingFlutterBinding], this binding also creates and owns a
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/// [renderView] to simplify bootstrapping for apps that have a dedicated main
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/// view.
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class ViewRenderingFlutterBinding extends RenderingFlutterBinding {
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/// Creates a binding for the rendering layer.
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///
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/// The `root` render box is attached directly to the [renderView] and is
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/// given constraints that require it to fill the window. The [renderView]
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/// itself is attached to the [rootPipelineOwner].
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///
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/// This binding does not automatically schedule any frames. Callers are
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/// responsible for deciding when to first call [scheduleFrame].
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ViewRenderingFlutterBinding({ RenderBox? root }) : _root = root;
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@override
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void initInstances() {
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super.initInstances();
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// TODO(goderbauer): Create window if embedder doesn't provide an implicit view.
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assert(PlatformDispatcher.instance.implicitView != null);
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_renderView = initRenderView(PlatformDispatcher.instance.implicitView!);
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_renderView.child = _root;
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_root = null;
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}
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RenderBox? _root;
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@override
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RenderView get renderView => _renderView;
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late RenderView _renderView;
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/// Creates a [RenderView] object to be the root of the
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/// [RenderObject] rendering tree, and initializes it so that it
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/// will be rendered when the next frame is requested.
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///
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/// Called automatically when the binding is created.
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RenderView initRenderView(FlutterView view) {
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final RenderView renderView = RenderView(view: view);
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rootPipelineOwner.rootNode = renderView;
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addRenderView(renderView);
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renderView.prepareInitialFrame();
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return renderView;
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}
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@override
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PipelineOwner createRootPipelineOwner() {
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return PipelineOwner(
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onSemanticsOwnerCreated: () {
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renderView.scheduleInitialSemantics();
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},
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onSemanticsUpdate: (SemanticsUpdate update) {
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renderView.updateSemantics(update);
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},
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onSemanticsOwnerDisposed: () {
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renderView.clearSemantics();
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},
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);
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}
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}
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