Improve hit testing

Now a RenderBox is considered hit if one of its children are hit or it itself
decides that it's hit. In particular, empty space inside a flex won't be hit
because none of the children are located there and a RenderFlex doesn't
consider itself hittable.

Fixes #53
Fixes #1221

packages/flutter/lib/src/material/icon_button.dart

@@ -22,6 +22,8 @@ class IconButton extends StatelessComponent {
   final VoidCallback onPressed;
 
   Widget build(BuildContext context) {
+    // TODO(abarth): We should use a radial reaction here so you can hit the
+    // 8.0 pixel padding as well as the icon.
     return new GestureDetector(
       onTap: onPressed,
       child: new Padding(

packages/flutter/lib/src/material/ink_well.dart

@@ -248,6 +248,8 @@ class _RenderInkSplashes extends RenderProxyBox {
       onLongPress();
   }
 
+  bool hitTestSelf(Point position) => true;
+
   void paint(PaintingContext context, Offset offset) {
     if (!_splashes.isEmpty) {
       final PaintingCanvas canvas = context.canvas;

packages/flutter/lib/src/material/tabs.dart

@@ -205,8 +205,8 @@ class _RenderTabBar extends RenderBox with
       reportLayoutChangedIfNeeded();
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 
   void _paintIndicator(PaintingCanvas canvas, RenderBox selectedTab, Offset offset) {

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

@@ -219,8 +219,8 @@ class RenderAutoLayout extends RenderBox
     // only indicates that the value has been flushed to the variable.
   }
 
-  void hitTestChildren(HitTestResult result, {Point position}) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, {Point position}) {
+    return defaultHitTestChildren(result, position: position);
   }
 
   void paint(PaintingContext context, Offset offset) {

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

@@ -219,8 +219,8 @@ class RenderBlock extends RenderBlockBase {
     defaultPaint(context, offset);
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 
 }
@@ -423,11 +423,11 @@ class RenderBlockViewport extends RenderBlockBase {
       transform.translate(startOffset, 0.0);
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
+  bool hitTestChildren(HitTestResult result, { Point position }) {
     if (isVertical)
-      defaultHitTestChildren(result, position: position + new Offset(0.0, -startOffset));
+      return defaultHitTestChildren(result, position: position + new Offset(0.0, -startOffset));
     else
-      defaultHitTestChildren(result, position: position + new Offset(-startOffset, 0.0));
+      return defaultHitTestChildren(result, position: position + new Offset(-startOffset, 0.0));
   }
 
   void debugDescribeSettings(List<String> settings) {

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

@@ -545,20 +545,25 @@ abstract class RenderBox extends RenderObject {
   bool hitTest(HitTestResult result, { Point position }) {
     if (position.x >= 0.0 && position.x < _size.width &&
         position.y >= 0.0 && position.y < _size.height) {
-      hitTestChildren(result, position: position);
-      result.add(new BoxHitTestEntry(this, position));
-      return true;
+      if (hitTestChildren(result, position: position) || hitTestSelf(position)) {
+        result.add(new BoxHitTestEntry(this, position));
+        return true;
+      }
     }
     return false;
   }
 
+  /// Override this function if this render object can be hit even if its
+  /// children were not hit
+  bool hitTestSelf(Point position) => false;
+
   /// Override this function to check whether any children are located at the
   /// given position
   ///
   /// Typically children should be hit tested in reverse paint order so that
   /// hit tests at locations where children overlap hit the child that is
   /// visually "on top" (i.e., paints later).
-  void hitTestChildren(HitTestResult result, { Point position }) { }
+  bool hitTestChildren(HitTestResult result, { Point position }) => false;
 
   /// Multiply the transform from the parent's coordinate system to this box's
   /// coordinate system into the given transform

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

@@ -108,7 +108,7 @@ class RenderCustomMultiChildLayoutBox extends RenderBox
     defaultPaint(context, offset);
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 }

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

@@ -30,6 +30,8 @@ class RenderErrorBox extends RenderBox {
 
   bool get sizedByParent => true;
 
+  bool hitTestSelf(Point position) => true;
+
   void performResize() {
     size = constraints.constrain(const Size(_kMaxWidth, _kMaxHeight));
   }

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

@@ -542,8 +542,8 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     }
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 
   void paint(PaintingContext context, Offset offset) {

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

@@ -134,8 +134,8 @@ class RenderGrid extends RenderBox with ContainerRenderObjectMixin<RenderBox, Gr
     }
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 
   void paint(PaintingContext context, Offset offset) {

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

@@ -179,6 +179,8 @@ class RenderImage extends RenderBox {
     return _sizeForConstraints(constraints).height;
   }
 
+  bool hitTestSelf(Point position) => true;
+
   void performLayout() {
     size = _sizeForConstraints(constraints);
   }

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

@@ -125,11 +125,8 @@ class RenderOverflowBox extends RenderBox with RenderObjectWithChildMixin<Render
       child.layout(_getInnerConstraints(constraints));
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null)
-      child.hitTest(result, position: position);
-    else
-      super.hitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return child?.hitTest(result, position: position) ?? false;
   }
 
   void paint(PaintingContext context, Offset offset) {
@@ -195,11 +192,8 @@ class RenderSizedOverflowBox extends RenderBox with RenderObjectWithChildMixin<R
       child.layout(constraints);
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null)
-      child.hitTest(result, position: position);
-    else
-      super.hitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return child?.hitTest(result, position: position) ?? false;
   }
 
   void paint(PaintingContext context, Offset offset) {

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

@@ -96,6 +96,8 @@ class RenderParagraph extends RenderBox {
     return textPainter.computeDistanceToActualBaseline(baseline);
   }
 
+  bool hitTestSelf(Point position) => true;
+
   void performLayout() {
     layoutText(constraints);
     size = constraints.constrain(textPainter.size);

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math' as math;
 import 'dart:ui' as ui;
 
 import 'package:flutter/painting.dart';
@@ -70,11 +71,8 @@ class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox
     }
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null)
-      child.hitTest(result, position: position);
-    else
-      super.hitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return child?.hitTest(result, position: position) ?? false;
   }
 
   void paint(PaintingContext context, Offset offset) {
@@ -625,6 +623,15 @@ class RenderClipOval extends RenderProxyBox {
     return _cachedPath;
   }
 
+  bool hitTest(HitTestResult result, { Point position }) {
+    Point center = size.center(Point.origin);
+    Offset offset = new Offset((position.x - center.x) / size.width,
+                               (position.y - center.y) / size.height);
+    if (offset.distance > 0.5)
+      return false;
+    return super.hitTest(result, position: position);
+  }
+
   void paint(PaintingContext context, Offset offset) {
     if (child != null) {
       Rect rect = offset & size;
@@ -706,6 +713,19 @@ class RenderDecoratedBox extends RenderProxyBox {
     super.detach();
   }
 
+  bool hitTestSelf(Point position) {
+    switch (_painter.decoration.shape) {
+      case Shape.rectangle:
+        // TODO(abarth): We should check the border radius.
+        return true;
+      case Shape.circle:
+        // Circles are inscribed into our smallest dimension.
+        Point center = size.center(Point.origin);
+        double distance = (position - center).distance;
+        return distance <= math.min(size.width, size.height) / 2.0;
+    }
+  }
+
   void paint(PaintingContext context, Offset offset) {
     assert(size.width != null);
     assert(size.height != null);
@@ -894,6 +914,7 @@ class RenderSizeObserver extends RenderProxyBox {
 
 /// Called when its time to paint into the given canvas
 typedef void CustomPaintCallback(PaintingCanvas canvas, Size size);
+typedef bool CustomHitTestCallback(Point position);
 
 /// Delegates its painting to [onPaint]
 ///
@@ -911,6 +932,7 @@ class RenderCustomPaint extends RenderProxyBox {
 
   RenderCustomPaint({
     CustomPaintCallback onPaint,
+    this.onHitTest,
     RenderBox child
   }) : super(child) {
     assert(onPaint != null);
@@ -931,11 +953,17 @@ class RenderCustomPaint extends RenderProxyBox {
     markNeedsPaint();
   }
 
+  CustomHitTestCallback onHitTest;
+
   void attach() {
     assert(_onPaint != null);
     super.attach();
   }
 
+  bool hitTestSelf(Point position) {
+    return onHitTest == null || onHitTest(position);
+  }
+
   void paint(PaintingContext context, Offset offset) {
     assert(_onPaint != null);
     context.canvas.translate(offset.dx, offset.dy);

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

@@ -60,12 +60,14 @@ abstract class RenderShiftedBox extends RenderBox with RenderObjectWithChildMixi
     }
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
+  bool hitTestChildren(HitTestResult result, { Point position }) {
     if (child != null) {
       final BoxParentData childParentData = child.parentData;
-      child.hitTest(result, position: new Point(position.x - childParentData.position.x,
-                                                position.y - childParentData.position.y));
+      final Point childPosition = new Point(position.x - childParentData.position.x,
+                                            position.y - childParentData.position.y);
+      return child.hitTest(result, position: childPosition);
     }
+    return false;
   }
 
 }

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

@@ -357,8 +357,8 @@ abstract class RenderStackBase extends RenderBox
     }
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    defaultHitTestChildren(result, position: position);
+  bool hitTestChildren(HitTestResult result, { Point position }) {
+    return defaultHitTestChildren(result, position: position);
   }
 
   void paintStack(PaintingContext context, Offset offset);
@@ -455,15 +455,15 @@ class RenderIndexedStack extends RenderStackBase {
     return child;
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
+  bool hitTestChildren(HitTestResult result, { Point position }) {
     if (firstChild == null)
-      return;
+      return false;
     assert(position != null);
     RenderBox child = _childAtIndex();
     final StackParentData childParentData = child.parentData;
     Point transformed = new Point(position.x - childParentData.position.x,
                                   position.y - childParentData.position.y);
-    child.hitTest(result, position: transformed);
+    return child.hitTest(result, position: transformed);
   }
 
   void paintStack(PaintingContext context, Offset offset) {

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

@@ -73,4 +73,6 @@ abstract class RenderToggleable extends RenderConstrainedBox {
     if (onChanged != null)
       onChanged(!_value);
   }
+
+  bool hitTestSelf(Point position) => true;
 }

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

@@ -160,11 +160,12 @@ class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox
     transform.translate(-scrollOffset.dx, -scrollOffset.dy);
   }
 
-  void hitTestChildren(HitTestResult result, { Point position }) {
+  bool hitTestChildren(HitTestResult result, { Point position }) {
     if (child != null) {
       assert(child.parentData is BoxParentData);
       Point transformed = position + _scrollOffsetRoundedToIntegerDevicePixels;
-      child.hitTest(result, position: transformed);
+      return child.hitTest(result, position: transformed);
     }
+    return false;
   }
 }

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

@@ -138,7 +138,7 @@ class DecoratedBox extends OneChildRenderObjectWidget {
 }
 
 class CustomPaint extends OneChildRenderObjectWidget {
-  CustomPaint({ Key key, this.onPaint, this.token, Widget child })
+  CustomPaint({ Key key, this.onPaint, this.onHitTest, this.token, Widget child })
     : super(key: key, child: child) {
     assert(onPaint != null);
   }
@@ -151,19 +151,23 @@ class CustomPaint extends OneChildRenderObjectWidget {
   /// has a more stable identity.
   final CustomPaintCallback onPaint;
 
+  final CustomHitTestCallback onHitTest;
+
   /// This widget repaints whenever you supply a new token.
   final Object token;
 
-  RenderCustomPaint createRenderObject() => new RenderCustomPaint(onPaint: onPaint);
+  RenderCustomPaint createRenderObject() => new RenderCustomPaint(onPaint: onPaint, onHitTest: onHitTest);
 
   void updateRenderObject(RenderCustomPaint renderObject, CustomPaint oldWidget) {
     if (oldWidget.token != token)
       renderObject.markNeedsPaint();
     renderObject.onPaint = onPaint;
+    renderObject.onHitTest = onHitTest;
   }
 
   void didUnmountRenderObject(RenderCustomPaint renderObject) {
     renderObject.onPaint = null;
+    renderObject.onHitTest = null;
   }
 }
 

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

@@ -17,29 +17,23 @@ const Color _kTransparent = const Color(0x00000000);
 class ModalBarrier extends StatelessComponent {
   ModalBarrier({
     Key key,
-    this.color
+    this.color: _kTransparent
   }) : super(key: key);
 
   final Color color;
 
   Widget build(BuildContext context) {
-    Widget child;
-
-    if (color != null) {
-      child = new DecoratedBox(
-        decoration: new BoxDecoration(
-          backgroundColor: color
-        )
-      );
-    }
-
     return new Listener(
       onPointerDown: (_) {
         Navigator.of(context).pop();
       },
       child: new ConstrainedBox(
         constraints: const BoxConstraints.expand(),
-        child: child
+        child: new DecoratedBox(
+          decoration: new BoxDecoration(
+            backgroundColor: color
+          )
+        )
       )
     );
   }

packages/unit/test/rendering/viewport_test.dart

@@ -5,8 +5,14 @@ import 'rendering_tester.dart';
 
 void main() {
   test('Should be able to hit with negative scroll offset', () {
+    RenderBox green = new RenderDecoratedBox(
+      decoration: new BoxDecoration(
+        backgroundColor: const Color(0xFF00FF00)
+      ));
+
     RenderBox size = new RenderConstrainedBox(
-      additionalConstraints: new BoxConstraints.tight(const Size(100.0, 100.0)));
+      additionalConstraints: new BoxConstraints.tight(const Size(100.0, 100.0)),
+      child: green);
 
     RenderBox red = new RenderDecoratedBox(
       decoration: new BoxDecoration(
@@ -21,10 +27,10 @@ void main() {
 
     result = new HitTestResult();
     renderView.hitTest(result, position: new Point(15.0, 0.0));
-    expect(result.path.first.target, equals(viewport));
+    expect(result.path.first.target.runtimeType, equals(TestRenderView));
 
     result = new HitTestResult();
     renderView.hitTest(result, position: new Point(15.0, 15.0));
-    expect(result.path.first.target, equals(size));
+    expect(result.path.first.target, equals(green));
   });
 }

packages/unit/test/widget/gesture_detector_test.dart

@@ -23,7 +23,11 @@ void main() {
         onVerticalDragEnd: (Offset velocity) {
           didEndDrag = true;
         },
-        child: new Container()
+        child: new Container(
+          decoration: const BoxDecoration(
+            backgroundColor: const Color(0xFF00FF00)
+          )
+        )
       );
 
       tester.pumpWidget(widget);
@@ -70,7 +74,11 @@ void main() {
         onVerticalDragEnd: (Offset velocity) { gestureCount += 1; },
         onHorizontalDragUpdate: (_) { fail("gesture should not match"); },
         onHorizontalDragEnd: (Offset velocity) { fail("gesture should not match"); },
-        child: new Container()
+        child: new Container(
+          decoration: const BoxDecoration(
+            backgroundColor: const Color(0xFF00FF00)
+          )
+        )
       );
       tester.pumpWidget(widget);
 
@@ -106,7 +114,11 @@ void main() {
           onPanEnd: (_) {
             didEndPan = true;
           },
-          child: new Container()
+          child: new Container(
+            decoration: const BoxDecoration(
+              backgroundColor: const Color(0xFF00FF00)
+            )
+          )
         )
       );
 

packages/unit/test/widget/snack_bar_test.dart

@@ -21,9 +21,14 @@ void main() {
                   content: new Text(helloSnackBar)
                 );
               },
-              child: new Center(
-                key: tapTarget,
-                child: new Placeholder(key: placeholderKey)
+              child: new Container(
+                decoration: const BoxDecoration(
+                  backgroundColor: const Color(0xFF00FF00)
+                ),
+                child: new Center(
+                  key: tapTarget,
+                  child: new Placeholder(key: placeholderKey)
+                )
               )
             );
           }

packages/unit/test/widget/transform_test.dart

@@ -33,7 +33,11 @@ void main() {
                   onTap: () {
                     didReceiveTap = true;
                   },
-                  child: new Container()
+                  child: new Container(
+                    decoration: new BoxDecoration(
+                      backgroundColor: new Color(0xFF00FFFF)
+                    )
+                  )
                 )
               )
             )
@@ -78,7 +82,11 @@ void main() {
                   onTap: () {
                     didReceiveTap = true;
                   },
-                  child: new Container()
+                  child: new Container(
+                    decoration: new BoxDecoration(
+                      backgroundColor: new Color(0xFF00FFFF)
+                    )
+                  )
                 )
               )
             )
@@ -124,7 +132,11 @@ void main() {
                   onTap: () {
                     didReceiveTap = true;
                   },
-                  child: new Container()
+                  child: new Container(
+                    decoration: new BoxDecoration(
+                      backgroundColor: new Color(0xFF00FFFF)
+                    )
+                  )
                 )
               )
             )