Implement clipPath Mutator for hcpp (#164525)

Implements `clipPath` mutator for hcpp.

Fixes https://github.com/flutter/flutter/issues/164219



https://github.com/user-attachments/assets/2c98e621-c73e-40ca-bc76-77de1a3826a0


## Pre-launch Checklist

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responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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[Discord]:
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---------

Co-authored-by: Gray Mackall <mackall@google.com>

dev/integration_tests/android_engine_test/lib/hcpp/platform_view_clippath_main.dart

@@ -0,0 +1,174 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:android_driver_extensions/extension.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_driver/driver_extension.dart';
+
+import '../src/allow_list_devices.dart';
+
+void main() async {
+  ensureAndroidDevice();
+  enableFlutterDriverExtension(
+    handler: (String? command) async {
+      return json.encode(<String, Object?>{
+        'supported': await HybridAndroidViewController.checkIfSupported(),
+      });
+    },
+    commands: <CommandExtension>[nativeDriverCommands],
+  );
+
+  // Run on full screen.
+  await SystemChrome.setEnabledSystemUIMode(SystemUiMode.immersive);
+  runApp(const _ComplicatedClipPathWrappedMainApp());
+}
+
+final class _ComplicatedClipPathWrappedMainApp extends StatefulWidget {
+  const _ComplicatedClipPathWrappedMainApp();
+
+  @override
+  State<_ComplicatedClipPathWrappedMainApp> createState() {
+    return _ComplicatedClipPathWrappedMainAppState();
+  }
+}
+
+class _ComplicatedClipPathWrappedMainAppState extends State<_ComplicatedClipPathWrappedMainApp> {
+  final CustomClipper<Path> _triangleClipper = TriangleClipper();
+  CustomClipper<Path>? _triangleOrEmpty = TriangleClipper();
+
+  void _toggleTriangleClipper() {
+    setState(() {
+      if (_triangleOrEmpty == null) {
+        _triangleOrEmpty = _triangleClipper;
+      } else {
+        _triangleOrEmpty = null;
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: ClipPath(
+        clipper: _triangleOrEmpty,
+        child: ClipPath(
+          clipper: CubicWaveClipper(),
+          child: ClipOval(
+            child: Stack(
+              alignment: Alignment.center,
+              children: <Widget>[
+                TextButton(
+                  key: const ValueKey<String>('ToggleTriangleClipping'),
+                  onPressed: _toggleTriangleClipper,
+                  child: const SizedBox(
+                    width: 500,
+                    height: 500,
+                    child: ColoredBox(color: Colors.green),
+                  ),
+                ),
+                const SizedBox(
+                  width: 400,
+                  height: 400,
+                  child: _HybridCompositionAndroidPlatformView(
+                    viewType: 'changing_color_button_platform_view',
+                  ),
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+// Clips to show the top half of the screen, with a cubic wave as the dividing
+// line.
+class CubicWaveClipper extends CustomClipper<Path> {
+  @override
+  Path getClip(Size size) {
+    final Path path = Path();
+    // Closer to 1 moves the wave lower, closer to 0 moves it higher.
+    final double waveHeight = size.height * 0.65;
+
+    path.lineTo(0, waveHeight);
+
+    path.cubicTo(
+      size.width * 0.25,
+      waveHeight * 0.8,
+      size.width * 0.75,
+      waveHeight * 1.2,
+      size.width,
+      waveHeight,
+    );
+
+    path.lineTo(size.width, 0);
+    path.lineTo(0, 0);
+
+    path.close();
+    return path;
+  }
+
+  @override
+  bool shouldReclip(CustomClipper<Path> oldClipper) {
+    return false;
+  }
+}
+
+// Clips a triangle off the top left of the screen.
+class TriangleClipper extends CustomClipper<Path> {
+  @override
+  Path getClip(Size size) {
+    final Path path = Path();
+    path.lineTo(0, size.height);
+    path.lineTo(size.width, size.height);
+    path.lineTo(size.width, 0);
+    path.lineTo(size.width / 2, 0);
+    path.lineTo(0, size.height / 2);
+    path.lineTo(0, size.height);
+    path.close();
+    return path;
+  }
+
+  @override
+  bool shouldReclip(CustomClipper<Path> oldClipper) {
+    return false;
+  }
+}
+
+final class _HybridCompositionAndroidPlatformView extends StatelessWidget {
+  const _HybridCompositionAndroidPlatformView({required this.viewType});
+
+  final String viewType;
+
+  @override
+  Widget build(BuildContext context) {
+    return PlatformViewLink(
+      viewType: viewType,
+      surfaceFactory: (BuildContext context, PlatformViewController controller) {
+        return AndroidViewSurface(
+          controller: controller as AndroidViewController,
+          gestureRecognizers: const <Factory<OneSequenceGestureRecognizer>>{},
+          hitTestBehavior: PlatformViewHitTestBehavior.transparent,
+        );
+      },
+      onCreatePlatformView: (PlatformViewCreationParams params) {
+        return PlatformViewsService.initHybridAndroidView(
+            id: params.id,
+            viewType: viewType,
+            layoutDirection: TextDirection.ltr,
+            creationParamsCodec: const StandardMessageCodec(),
+          )
+          ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
+          ..create();
+      },
+    );
+  }
+}

dev/integration_tests/android_engine_test/test_driver/hcpp/platform_view_clippath_main_test.dart

@@ -0,0 +1,77 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:android_driver_extensions/native_driver.dart';
+import 'package:android_driver_extensions/skia_gold.dart';
+import 'package:flutter_driver/flutter_driver.dart';
+import 'package:test/test.dart';
+
+import '../_luci_skia_gold_prelude.dart';
+
+/// For local debugging, a (local) golden-file is required as a baseline:
+///
+/// ```sh
+/// # Checkout HEAD, i.e. *before* changes you want to test.
+/// UPDATE_GOLDENS=1 flutter drive lib/hcpp/platform_view_clippath_main.dart
+///
+/// # Make your changes.
+///
+/// # Run the test against baseline.
+/// flutter drive lib/hcpp/platform_view_clippath_main.dart
+/// ```
+///
+/// For a convenient way to deflake a test, see `tool/deflake.dart`.
+void main() async {
+  const String goldenPrefix = 'hybrid_composition_pp_platform_view';
+
+  late final FlutterDriver flutterDriver;
+  late final NativeDriver nativeDriver;
+
+  setUpAll(() async {
+    if (isLuci) {
+      await enableSkiaGoldComparator(namePrefix: 'android_engine_test$goldenVariant');
+    }
+    flutterDriver = await FlutterDriver.connect();
+    nativeDriver = await AndroidNativeDriver.connect(flutterDriver);
+    await nativeDriver.configureForScreenshotTesting();
+    await flutterDriver.waitUntilFirstFrameRasterized();
+  });
+
+  tearDownAll(() async {
+    await nativeDriver.close();
+    await flutterDriver.close();
+  });
+
+  test('verify that HCPP is supported and enabled', () async {
+    final Map<String, Object?> response =
+        json.decode(await flutterDriver.requestData('')) as Map<String, Object?>;
+
+    expect(response['supported'], true);
+  }, timeout: Timeout.none);
+
+  test('should screenshot a platform view with specified clippath', () async {
+    await expectLater(
+      nativeDriver.screenshot(),
+      matchesGoldenFile('$goldenPrefix.complex_clippath.png'),
+    );
+  }, timeout: Timeout.none);
+
+  test(
+    'should start with triangle cutoff on left, and toggle to no triangle cutoff on left',
+    () async {
+      await expectLater(
+        nativeDriver.screenshot(),
+        matchesGoldenFile('$goldenPrefix.complex_clippath.png'),
+      );
+      await flutterDriver.tap(find.byValueKey('ToggleTriangleClipping'));
+      await expectLater(
+        nativeDriver.screenshot(),
+        matchesGoldenFile('$goldenPrefix.complex_clippath_no_triangle.png'),
+      );
+    },
+    timeout: Timeout.none,
+  );
+}