Basic view management for engine classes

ci/licenses_golden/licenses_flutter

@@ -1904,8 +1904,6 @@ ORIGIN: ../../../flutter/lib/ui/window/pointer_data_packet_converter.cc + ../../
 ORIGIN: ../../../flutter/lib/ui/window/pointer_data_packet_converter.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/window/viewport_metrics.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/window/viewport_metrics.h + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/lib/ui/window/window.cc + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/lib/ui/window/window.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/annotations.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/canvas.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/channel_buffers.dart + ../../../flutter/LICENSE
@@ -4634,8 +4632,6 @@ FILE: ../../../flutter/lib/ui/window/pointer_data_packet_converter.cc
 FILE: ../../../flutter/lib/ui/window/pointer_data_packet_converter.h
 FILE: ../../../flutter/lib/ui/window/viewport_metrics.cc
 FILE: ../../../flutter/lib/ui/window/viewport_metrics.h
-FILE: ../../../flutter/lib/ui/window/window.cc
-FILE: ../../../flutter/lib/ui/window/window.h
 FILE: ../../../flutter/lib/web_ui/lib/annotations.dart
 FILE: ../../../flutter/lib/web_ui/lib/canvas.dart
 FILE: ../../../flutter/lib/web_ui/lib/channel_buffers.dart

common/constants.h

@@ -7,6 +7,32 @@
 
 namespace flutter {
 constexpr double kMegaByteSizeInBytes = (1 << 20);
+
+// The ID for the implicit view if the implicit view is enabled.
+//
+// The implicit view is a compatibility mechanism to help the transition from
+// the older single-view APIs to the newer multi-view APIs. The two sets of APIs
+// use different models for view management. The implicit view mechanism allows
+// single-view APIs to operate a special view as if other views don't exist.
+//
+// In the regular multi-view model, all views should be created by
+// `Shell::AddView` before being used, and removed by `Shell::RemoveView` to
+// signify that they are gone. If a view is added or removed, the framework
+// (`PlatformDispatcher`) will be notified. New view IDs are always unique,
+// never reused. Operating a non-existing view is an error.
+//
+// The implicit view is another special view in addition to the "regular views"
+// as above. The shell starts up having the implicit view, which has a fixed
+// view ID of `kFlutterImplicitViewId` and is available throughout the lifetime
+// of the shell. `Shell::AddView` or `RemoveView` must not be called for this
+// view. Even when the window that shows the view is closed, the framework is
+// unaware and might continue rendering into or operating this view.
+//
+// The single-view APIs, which are APIs that do not specify view IDs, operate
+// the implicit view. The multi-view APIs can operate all views, including the
+// implicit view if the target ID is `kFlutterImplicitViewId`, unless specified
+// otherwise.
+constexpr int64_t kFlutterImplicitViewId = 0;
 }  // namespace flutter
 
 #endif  // FLUTTER_COMMON_CONSTANTS_H_

lib/ui/BUILD.gn

@@ -155,8 +155,6 @@ source_set("ui") {
     "window/pointer_data_packet_converter.h",
     "window/viewport_metrics.cc",
     "window/viewport_metrics.h",
-    "window/window.cc",
-    "window/window.h",
   ]
 
   public_configs = [ "//flutter:config" ]

lib/ui/compositing/scene.cc

@@ -10,7 +10,6 @@
 #include "flutter/lib/ui/painting/picture.h"
 #include "flutter/lib/ui/ui_dart_state.h"
 #include "flutter/lib/ui/window/platform_configuration.h"
-#include "flutter/lib/ui/window/window.h"
 #if IMPELLER_SUPPORTS_RENDERING
 #include "flutter/lib/ui/painting/display_list_deferred_image_gpu_impeller.h"
 #endif  // IMPELLER_SUPPORTS_RENDERING

lib/ui/dart_ui.cc

@@ -7,6 +7,7 @@
 #include <mutex>
 #include <string_view>
 
+#include "flutter/common/constants.h"
 #include "flutter/common/settings.h"
 #include "flutter/fml/build_config.h"
 #include "flutter/lib/ui/compositing/scene.h"
@@ -95,7 +96,6 @@ typedef CanvasPath Path;
   V(IsolateNameServerNatives::RemovePortNameMapping, 1)               \
   V(NativeStringAttribute::initLocaleStringAttribute, 4)              \
   V(NativeStringAttribute::initSpellOutStringAttribute, 3)            \
-  V(PlatformConfigurationNativeApi::ImplicitViewEnabled, 0)           \
   V(PlatformConfigurationNativeApi::DefaultRouteName, 0)              \
   V(PlatformConfigurationNativeApi::ScheduleFrame, 0)                 \
   V(PlatformConfigurationNativeApi::Render, 1)                        \
@@ -373,6 +373,12 @@ void DartUI::InitForIsolate(const Settings& settings) {
       Dart_PropagateError(result);
     }
   }
+
+  result = Dart_SetField(dart_ui, ToDart("_implicitViewId"),
+                         Dart_NewInteger(kFlutterImplicitViewId));
+  if (Dart_IsError(result)) {
+    Dart_PropagateError(result);
+  }
 }
 
 }  // namespace flutter

lib/ui/hooks.dart

@@ -4,6 +4,60 @@
 
 part of dart.ui;
 
+@pragma('vm:entry-point')
+void _addView(
+  int viewId,
+  double devicePixelRatio,
+  double width,
+  double height,
+  double viewPaddingTop,
+  double viewPaddingRight,
+  double viewPaddingBottom,
+  double viewPaddingLeft,
+  double viewInsetTop,
+  double viewInsetRight,
+  double viewInsetBottom,
+  double viewInsetLeft,
+  double systemGestureInsetTop,
+  double systemGestureInsetRight,
+  double systemGestureInsetBottom,
+  double systemGestureInsetLeft,
+  double physicalTouchSlop,
+  List<double> displayFeaturesBounds,
+  List<int> displayFeaturesType,
+  List<int> displayFeaturesState,
+  int displayId,
+) {
+  final _ViewConfiguration viewConfiguration = _buildViewConfiguration(
+    devicePixelRatio,
+    width,
+    height,
+    viewPaddingTop,
+    viewPaddingRight,
+    viewPaddingBottom,
+    viewPaddingLeft,
+    viewInsetTop,
+    viewInsetRight,
+    viewInsetBottom,
+    viewInsetLeft,
+    systemGestureInsetTop,
+    systemGestureInsetRight,
+    systemGestureInsetBottom,
+    systemGestureInsetLeft,
+    physicalTouchSlop,
+    displayFeaturesBounds,
+    displayFeaturesType,
+    displayFeaturesState,
+    displayId,
+  );
+  PlatformDispatcher.instance._addView(viewId, viewConfiguration);
+}
+
+@pragma('vm:entry-point')
+void _removeView(int viewId) {
+  PlatformDispatcher.instance._removeView(viewId);
+}
+
 @pragma('vm:entry-point')
 void _updateDisplays(
   List<int> ids,

lib/ui/natives.dart

@@ -112,3 +112,12 @@ _ScheduleImmediateClosure _getScheduleMicrotaskClosure() => _scheduleMicrotask;
 // rendering.
 @pragma('vm:entry-point')
 bool _impellerEnabled = false;
+
+// Used internally to indicate whether the embedder enables the implicit view,
+// and the implicit view's ID if so.
+//
+// The exact value of this variable is an implementation detail that may change
+// at any time. Apps should always use PlatformDispatcher.implicitView to
+// determine the current implicit view, if any.
+@pragma('vm:entry-point')
+int? _implicitViewId;

lib/ui/painting/canvas.cc

@@ -13,7 +13,6 @@
 #include "flutter/lib/ui/painting/paint.h"
 #include "flutter/lib/ui/ui_dart_state.h"
 #include "flutter/lib/ui/window/platform_configuration.h"
-#include "flutter/lib/ui/window/window.h"
 
 using tonic::ToDart;
 
@@ -621,11 +620,16 @@ void Canvas::drawShadow(const CanvasPath* path,
   }
 
   // Not using SafeNarrow because DPR will always be a relatively small number.
-  SkScalar dpr = static_cast<float>(UIDartState::Current()
-                                        ->platform_configuration()
-                                        ->get_window(0)
-                                        ->viewport_metrics()
-                                        .device_pixel_ratio);
+  const ViewportMetrics* metrics =
+      UIDartState::Current()->platform_configuration()->GetMetrics(0);
+  SkScalar dpr;
+  // TODO(dkwingsmt): We should support rendering shadows on non-implicit views.
+  // However, currently this method has no way to get the target view ID.
+  if (metrics == nullptr) {
+    dpr = 1.0f;
+  } else {
+    dpr = static_cast<float>(metrics->device_pixel_ratio);
+  }
   if (display_list_builder_) {
     // The DrawShadow mechanism results in non-public operations to be
     // performed on the canvas involving an SkDrawShadowRec. Since we

lib/ui/platform_dispatcher.dart

@@ -66,14 +66,6 @@ typedef ErrorCallback = bool Function(Object exception, StackTrace stackTrace);
 // A gesture setting value that indicates it has not been set by the engine.
 const double _kUnsetGestureSetting = -1.0;
 
-// The view ID of PlatformDispatcher.implicitView. This is an
-// implementation detail that may change at any time. Apps
-// should always use PlatformDispatcher.implicitView to determine
-// the current implicit view, if any.
-//
-// Keep this in sync with kImplicitViewId in window/platform_configuration.cc.
-const int _kImplicitViewId = 0;
-
 // A message channel to receive KeyData from the platform.
 //
 // See embedder.cc::kFlutterKeyDataChannel for more information.
@@ -218,10 +210,29 @@ class PlatformDispatcher {
   /// * [View.of], for accessing the current view.
   /// * [PlatformDispatcher.views] for a list of all [FlutterView]s provided
   ///   by the platform.
-  FlutterView? get implicitView => _implicitViewEnabled() ? _views[_kImplicitViewId] : null;
-
-  @Native<Handle Function()>(symbol: 'PlatformConfigurationNativeApi::ImplicitViewEnabled')
-  external static bool _implicitViewEnabled();
+  FlutterView? get implicitView {
+    final FlutterView? result = _views[_implicitViewId];
+    // Make sure [implicitView] agrees with `_implicitViewId`.
+    assert((result != null) == (_implicitViewId != null),
+      (_implicitViewId != null) ?
+        'The implicit view ID is $_implicitViewId, but the implicit view does not exist.' :
+        'The implicit view ID is null, but the implicit view exists.');
+    // Make sure [implicitView] never chages.
+    assert(() {
+      if (_debugRecordedLastImplicitView) {
+        assert(identical(_debugLastImplicitView, result),
+          'The implicitView has changed:\n'
+          'Last: $_debugLastImplicitView\nCurrent: $result');
+      } else {
+        _debugLastImplicitView = result;
+        _debugRecordedLastImplicitView = true;
+      }
+      return true;
+    }());
+    return result;
+  }
+  FlutterView? _debugLastImplicitView;
+  bool _debugRecordedLastImplicitView = false;
 
   /// A callback that is invoked whenever the [ViewConfiguration] of any of the
   /// [views] changes.
@@ -249,6 +260,34 @@ class PlatformDispatcher {
     _onMetricsChangedZone = Zone.current;
   }
 
+  // Called from the engine, via hooks.dart
+  //
+  // Adds a new view with the specific view configuration.
+  //
+  // The implicit view must be added before [implicitView] is first called,
+  // which is typically the main function.
+  void _addView(int id, _ViewConfiguration viewConfiguration) {
+    assert(!_views.containsKey(id), 'View ID $id already exists.');
+    _views[id] = FlutterView._(id, this, viewConfiguration);
+    _invoke(onMetricsChanged, _onMetricsChangedZone);
+  }
+
+  // Called from the engine, via hooks.dart
+  //
+  // Removes the specific view.
+  //
+  // The target view must must exist. The implicit view must not be removed,
+  // or an assertion will be triggered.
+  void _removeView(int id) {
+    assert(id != _implicitViewId, 'The implicit view #$id can not be removed.');
+    if (id == _implicitViewId) {
+      return;
+    }
+    assert(_views.containsKey(id), 'View ID $id does not exist.');
+    _views.remove(id);
+    _invoke(onMetricsChanged, _onMetricsChangedZone);
+  }
+
   // Called from the engine, via hooks.dart.
   //
   // Updates the available displays.
@@ -264,15 +303,8 @@ class PlatformDispatcher {
   //
   // Updates the metrics of the window with the given id.
   void _updateWindowMetrics(int viewId, _ViewConfiguration viewConfiguration) {
-    final FlutterView? view = _views[viewId];
-    if (viewId == _kImplicitViewId && view == null) {
-      // TODO(goderbauer): Remove the implicit creation of the implicit view
-      //   when we have an addView API and the implicit view is added via that.
-      _views[viewId] = FlutterView._(viewId, this, viewConfiguration);
-    } else {
-      assert(view != null);
-      view!._viewConfiguration = viewConfiguration;
-    }
+    assert(_views.containsKey(viewId), 'View $viewId does not exist.');
+    _views[viewId]!._viewConfiguration = viewConfiguration;
     _invoke(onMetricsChanged, _onMetricsChangedZone);
   }
 

lib/ui/ui_dart_state.cc

@@ -9,6 +9,7 @@
 
 #include "flutter/fml/message_loop.h"
 #include "flutter/lib/ui/window/platform_configuration.h"
+#include "flutter/lib/ui/window/platform_message.h"
 #include "third_party/tonic/converter/dart_converter.h"
 #include "third_party/tonic/dart_message_handler.h"
 

lib/ui/window.dart

@@ -406,7 +406,11 @@ class SingletonFlutterWindow extends FlutterView {
     'This feature was deprecated after v3.7.0-32.0.pre.'
   )
   SingletonFlutterWindow._() : super._(
-    _kImplicitViewId,
+    // TODO(dkwingsmt): This crashes if the implicit view is disabled. We need
+    // to resolve this by the time embedders are allowed to disable the implicit
+    // view.
+    // https://github.com/flutter/flutter/issues/131651
+    _implicitViewId!,
     PlatformDispatcher.instance,
     const _ViewConfiguration(),
   );