ClipPath (#3695)

* ClipPath

* Add a test for ClipOval and ClipPath

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

@@ -857,7 +857,13 @@ abstract class _RenderCustomClip<T> extends RenderProxyBox {
   }
 
   T get _defaultClip;
-  T get _clip => _clipper?.getClip(size) ?? _defaultClip;
+  T _clip;
+
+  @override
+  void performLayout() {
+    super.performLayout();
+    _clip = _clipper?.getClip(size) ?? _defaultClip;
+  }
 
   @override
   Rect describeApproximatePaintClip(RenderObject child) => _clipper?.getApproximateClipRect(size) ?? Point.origin & size;
@@ -994,6 +1000,40 @@ class RenderClipOval extends _RenderCustomClip<Rect> {
   }
 }
 
+/// Clips its child using a path.
+///
+/// Takes a delegate whose primary method returns a path that should
+/// be used to prevent the child from painting outside the path.
+///
+/// Clipping to a path is expensive. Certain shapes have more
+/// optimized render objects:
+///
+///  * To clip to a rectangle, consider [RenderClipRect].
+///  * To clip to an oval or circle, consider [RenderClipOval].
+///  * To clip to a rounded rectangle, consider [RenderClipRRect].
+class RenderClipPath extends _RenderCustomClip<Path> {
+  RenderClipPath({
+    RenderBox child,
+    CustomClipper<Path> clipper
+  }) : super(child: child, clipper: clipper);
+
+  @override
+  Path get _defaultClip => new Path()..addRect(Point.origin & size);
+
+  @override
+  bool hitTest(HitTestResult result, { Point position }) {
+    if (_clip == null || !_clip.contains(position))
+      return false;
+    return super.hitTest(result, position: position);
+  }
+
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null)
+      context.pushClipPath(needsCompositing, offset, Point.origin & size, _clip, super.paint);
+  }
+}
+
 /// Where to paint a box decoration.
 enum DecorationPosition {
   /// Paint the box decoration behind the children.

packages/flutter/lib/src/widgets/basic.dart

@@ -293,6 +293,14 @@ class ClipOval extends SingleChildRenderObjectWidget {
   ClipOval({ Key key, this.clipper, Widget child }) : super(key: key, child: child);
 
   /// If non-null, determines which clip to use.
+  ///
+  /// The delegate returns a rectangle that describes the axis-aligned
+  /// bounding box of the oval. The oval's axes will themselves also
+  /// be axis-aligned.
+  ///
+  /// If the [clipper] delegate is null, then the oval uses the
+  /// widget's bounding box (the layout dimensions of the render
+  /// object) instead.
   final CustomClipper<Rect> clipper;
 
   @override
@@ -309,6 +317,42 @@ class ClipOval extends SingleChildRenderObjectWidget {
   }
 }
 
+/// Clips its child using a path.
+///
+/// Invokes a callback on a delegate whenever the widget is to be
+/// painted. The callback returns a path and the widget prevents the
+/// child from painting outside the path.
+///
+/// Clipping to a path is expensive. Certain shapes have more
+/// optimized widgets:
+///
+///  * To clip to a rectangle, consider [ClipRect].
+///  * To clip to an oval or circle, consider [ClipOval].
+///  * To clip to a rounded rectangle, consider [ClipRRect].
+class ClipPath extends SingleChildRenderObjectWidget {
+  ClipPath({ Key key, this.clipper, Widget child }) : super(key: key, child: child);
+
+  /// If non-null, determines which clip to use.
+  ///
+  /// The default clip, which is used if this property is null, is the
+  /// bounding box rectangle of the widget. [ClipRect] is a more
+  /// efficient way of obtaining that effect.
+  final CustomClipper<Path> clipper;
+
+  @override
+  RenderClipPath createRenderObject(BuildContext context) => new RenderClipPath(clipper: clipper);
+
+  @override
+  void updateRenderObject(BuildContext context, RenderClipPath renderObject) {
+    renderObject.clipper = clipper;
+  }
+
+  @override
+  void didUnmountRenderObject(RenderClipPath renderObject) {
+    renderObject.clipper = null;
+  }
+}
+
 
 // POSITIONING AND SIZING NODES
 

packages/flutter/test/widget/clip_test.dart

+// Copyright 2015 The Chromium 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 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/material.dart';
+import 'package:test/test.dart';
+
+final List<String> log = <String>[];
+
+class PathClipper extends CustomClipper<Path> {
+  @override
+  Path getClip(Size size) {
+    log.add('getClip');
+    return new Path()
+      ..addRect(new Rect.fromLTWH(50.0, 50.0, 100.0, 100.0));
+  }
+  @override
+  bool shouldRepaint(PathClipper oldWidget) => false;
+}
+
+void main() {
+  testWidgets('ClipPath', (WidgetTester tester) {
+    tester.pumpWidget(
+      new ClipPath(
+        clipper: new PathClipper(),
+        child: new GestureDetector(
+          behavior: HitTestBehavior.opaque,
+          onTap: () { log.add('tap'); },
+          child: new Container()
+        )
+      )
+    );
+    expect(log, equals(['getClip']));
+
+    tester.tapAt(new Point(10.0, 10.0));
+    expect(log, equals(['getClip']));
+    log.clear();
+
+    tester.tapAt(new Point(100.0, 100.0));
+    expect(log, equals(['tap']));
+    log.clear();
+  });
+
+  testWidgets('ClipOval', (WidgetTester tester) {
+    tester.pumpWidget(
+      new ClipOval(
+        child: new GestureDetector(
+          behavior: HitTestBehavior.opaque,
+          onTap: () { log.add('tap'); },
+          child: new Container()
+        )
+      )
+    );
+    expect(log, equals([]));
+
+    tester.tapAt(new Point(10.0, 10.0));
+    expect(log, equals([]));
+    log.clear();
+
+    tester.tapAt(new Point(400.0, 300.0));
+    expect(log, equals(['tap']));
+    log.clear();
+  });
+}