Remove LiveTestRenderView (flutter#127882)

In the multi view world, `RenderViews` are created by the `View` widget and no longer owned by the binding. Prior to this change, the `LiveTestWidgetsFlutterBinding` owned and managed a special subclass of `RenderView`, the `_LiveTestRenderView`. In the new world, where `RenderView`s can be created anywhere in the widget tree where a `View` widget is used, this setup is no longer feasible. This change removes this special `_LiveTestRenderView` and instead adds debug hocks to `RenderView` to allow the `LiveTestWidgetsFlutterBinding` to draw a debug overlay on top of the content of any `RenderView`.

Author: goderbauer

packages/flutter/lib/src/rendering/view.dart

@@ -33,6 +33,10 @@ class ViewConfiguration {
   final double devicePixelRatio;
 
   /// Creates a transformation matrix that applies the [devicePixelRatio].
+  ///
+  /// The matrix translates points from the local coordinate system of the
+  /// app (in logical pixels) to the global coordinate system of the
+  /// [FlutterView] (in physical pixels).
   Matrix4 toMatrix() {
     return Matrix4.diagonal3Values(devicePixelRatio, devicePixelRatio, 1.0);
   }
@@ -212,6 +216,15 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     if (child != null) {
       context.paintChild(child!, offset);
     }
+    assert(() {
+      final List<DebugPaintCallback> localCallbacks = _debugPaintCallbacks.toList();
+      for (final DebugPaintCallback paintCallback in localCallbacks) {
+        if (_debugPaintCallbacks.contains(paintCallback)) {
+          paintCallback(context, offset, this);
+        }
+      }
+      return true;
+    }());
   }
 
   @override
@@ -381,4 +394,47 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
       properties.add(DiagnosticsNode.message('semantics enabled'));
     }
   }
+
+  static final List<DebugPaintCallback> _debugPaintCallbacks = <DebugPaintCallback>[];
+
+  /// Registers a [DebugPaintCallback] that is called every time a [RenderView]
+  /// repaints in debug mode.
+  ///
+  /// The callback may paint a debug overlay on top of the content of the
+  /// [RenderView] provided to the callback. Callbacks are invoked in the
+  /// order they were registered in.
+  ///
+  /// Neither registering a callback nor the continued presence of a callback
+  /// changes how often [RenderView]s are repainted. It is up to the owner of
+  /// the callback to call [markNeedsPaint] on any [RenderView] for which it
+  /// wants to update the painted overlay.
+  ///
+  /// Does nothing in release mode.
+  static void debugAddPaintCallback(DebugPaintCallback callback) {
+    assert(() {
+      _debugPaintCallbacks.add(callback);
+      return true;
+    }());
+  }
+
+  /// Removes a callback registered with [debugAddPaintCallback].
+  ///
+  /// It does not schedule a frame to repaint the [RenderView]s without the
+  /// overlay painted by the removed callback. It is up to the owner of the
+  /// callback to call [markNeedsPaint] on the relevant [RenderView]s to
+  /// repaint them without the overlay.
+  ///
+  /// Does nothing in release mode.
+  static void debugRemovePaintCallback(DebugPaintCallback callback) {
+    assert(() {
+      _debugPaintCallbacks.remove(callback);
+      return true;
+    }());
+  }
 }
+
+/// A callback for painting a debug overlay on top of the provided [RenderView].
+///
+/// Used by [RenderView.debugAddPaintCallback] and
+/// [RenderView.debugRemovePaintCallback].
+typedef DebugPaintCallback = void Function(PaintingContext context, Offset offset, RenderView renderView);

packages/flutter/test/rendering/view_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import 'mock_canvas.dart';
 import 'rendering_tester.dart';
 
 void main() {
@@ -69,4 +70,76 @@ void main() {
     expect(viewConfigurationA.hashCode, viewConfigurationB.hashCode);
     expect(viewConfigurationA.hashCode != viewConfigurationC.hashCode, true);
   });
+
+  test('invokes DebugPaintCallback', () {
+    final PaintPattern paintsOrangeRect = paints..rect(
+      color: orange,
+      rect: orangeRect,
+    );
+    final PaintPattern paintsGreenRect = paints..rect(
+      color: green,
+      rect: greenRect,
+    );
+    final PaintPattern paintOrangeAndGreenRect = paints
+      ..rect(
+        color: orange,
+        rect: orangeRect,
+      )
+      ..rect(
+        color: green,
+        rect: greenRect,
+      );
+    void paintCallback(PaintingContext context, Offset offset, RenderView renderView) {
+      context.canvas.drawRect(
+        greenRect,
+        Paint()..color = green,
+      );
+    }
+
+    layout(TestRenderObject());
+    expect(
+      TestRenderingFlutterBinding.instance.renderView,
+      paintsOrangeRect,
+    );
+    expect(
+      TestRenderingFlutterBinding.instance.renderView,
+      isNot(paintsGreenRect),
+    );
+
+    RenderView.debugAddPaintCallback(paintCallback);
+    expect(
+      TestRenderingFlutterBinding.instance.renderView,
+      paintOrangeAndGreenRect,
+    );
+
+    RenderView.debugRemovePaintCallback(paintCallback);
+    expect(
+      TestRenderingFlutterBinding.instance.renderView,
+      paintsOrangeRect,
+    );
+    expect(
+      TestRenderingFlutterBinding.instance.renderView,
+      isNot(paintsGreenRect),
+    );
+  });
+}
+
+const Color orange = Color(0xFFFF9000);
+const Color green = Color(0xFF0FF900);
+const Rect orangeRect = Rect.fromLTWH(10, 10, 50, 75);
+const Rect greenRect = Rect.fromLTWH(20, 20, 100, 150);
+
+class TestRenderObject extends RenderBox {
+  @override
+  void performLayout() {
+    size = constraints.biggest;
+  }
+
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    context.canvas.drawRect(
+      orangeRect,
+      Paint()..color = orange,
+    );
+  }
 }