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")
* Reland "Inject current `FlutterView` into tree and make available via `View.of(context)` (#116924)"
This reverts commit 9102f2fe0bd26db6074ac4a17785296cd341ecb9.
* remove window placeholder
This turns on order shuffling for all tests that don't fail with it on, marking those tests that do fail with a tag so that they will be run without shuffling on.
To determine which tests fail with it on, I ran all the tests 100 times with different random shuffle seeds, and then also ran it with the date seeds from today until the end of July, and tagged all of the test suites (files) that fail, with a seed that caused them to fail.
Adds MediaQuery.maybeOf to replace calling MediaQuery.of(context, nullOk: true), and removes the nullOk parameter. Also changes MediaQuery.of to return a non-nullable value, and removes many instances of the ! operator, reducing the possible places where a null dereference could occur.
* Update project.pbxproj files to say Flutter rather than Chromium
Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.
* Update the copyright notice checker to require a standard notice on all files
* Update copyrights on Dart files. (This was a mechanical commit.)
* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.
Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).
* Clean up the copyrights in non-Dart files. (Manual edits.)
Also, make sure templates don't have copyrights.
* Fix some more ORGANIZATIONNAMEs
* Add structured errors in Animations, TabView, ChangeNotifier
* Add structured error on MaterialPageRoute, BoxBorder, DecorationImagePainter, TextSpan
* Add structured errors in Debug
* Fix test errors
* Add structured errors in Scaffold and Stepper
* Add structured errors in part of Rendering Layer
* Fix failing test due to FloatingPoint precision
* Fix failing tests due to precision error and not using final
* Fix failing test due to floating precision error with RegEx instead
* Add structured error in CustomLayout and increase test coverage
* Add structured error & its test in ListBody
* Add structured error in ProxyBox and increase test coverage
* Add structured error message in Viewport
* Fix styles and add more assertions on ErrorHint and DiagnosticProperty
* Add structured error in scheduler/binding and scheduler/ticker
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Add structured error in AssetBundle and TextInput
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Add structured errors in several widgets #1
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Remove unused import
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Add assertions on hint messages
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Fix catch spacing
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Add structured error in several widgets part 2 and increase code coverage
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Add structured error in flutter_test/widget_tester
* Fix floating precision accuracy by using RegExp
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Remove todo to add tests in Scaffold showBottomSheet
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Fix reviews by indenting lines and fixing the assertion orders
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Fix failing tests due to renaming class
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Try skipping the NetworkBundleTest
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
* Remove leading space in material/debug error hint
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>
