Add debugDumpLayerTree to dump the layer tree

To help debugging issues with the layer tree.

examples/stocks/lib/stock_home.dart

@@ -107,7 +107,7 @@ class StockHomeState extends State<StockHome> {
         ),
         new DrawerItem(
           icon: 'device/dvr',
-          onPressed: () { debugDumpApp(); debugDumpRenderTree(); },
+          onPressed: () { debugDumpApp(); debugDumpRenderTree(); debugDumpLayerTree(); },
           child: new Text('Dump App to Console')
         ),
         new DrawerDivider(),

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

@@ -292,3 +292,8 @@ class FlutterBinding extends HitTestTarget {
 void debugDumpRenderTree() {
   debugPrint(FlutterBinding.instance.renderView.toStringDeep());
 }
+
+/// Prints a textual representation of the entire layer tree
+void debugDumpLayerTree() {
+  debugPrint(FlutterBinding.instance.renderView.layer.toStringDeep());
+}

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

@@ -6,6 +6,8 @@ import 'dart:ui' as ui;
 import 'dart:async';
 import 'dart:collection';
 
+import 'package:vector_math/vector_math_64.dart';
+
 /// Causes each RenderBox to paint a box around its bounds.
 bool debugPaintSizeEnabled = false;
 
@@ -36,6 +38,12 @@ int debugPaintPointersColorValue = 0x00BBBB;
 /// The color to use when painting RenderError boxes in checked mode.
 ui.Color debugErrorBoxColor = const ui.Color(0xFFFF0000);
 
+List<String> debugDescribeTransform(Matrix4 transform) {
+  List<String> matrix = transform.toString().split('\n').map((String s) => '  $s').toList();
+  matrix.removeLast();
+  return matrix;
+}
+
 /// Prints a message to the console, which you can access using the "flutter"
 /// tool's "logs" command ("flutter logs").
 ///

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

@@ -7,6 +7,7 @@ import 'dart:ui' as ui;
 import 'package:vector_math/vector_math_64.dart';
 
 import 'basic_types.dart';
+import 'debug.dart';
 
 export 'basic_types.dart';
 
@@ -66,6 +67,31 @@ abstract class Layer {
   /// The layerOffset is the accumulated offset of this layer's parent from the
   /// origin of the builder's coordinate system.
   void addToScene(ui.SceneBuilder builder, Offset layerOffset);
+
+  String toString() => '$runtimeType';
+
+  dynamic debugOwner;
+
+  String toStringDeep([String prefixLineOne = '', String prefixOtherLines = '']) {
+    String result = '$prefixLineOne$this\n';
+    final String childrenDescription = debugDescribeChildren(prefixOtherLines);
+    final String settingsPrefix = childrenDescription != '' ? '$prefixOtherLines \u2502 ' : '$prefixOtherLines   ';
+    List<String> settings = <String>[];
+    debugDescribeSettings(settings);
+    result += settings.map((String setting) => "$settingsPrefix$setting\n").join();
+    if (childrenDescription == '')
+      result += '$prefixOtherLines\n';
+    result += childrenDescription;
+    return result;
+  }
+
+  void debugDescribeSettings(List<String> settings) {
+    if (debugOwner != null)
+      settings.add('owner: $debugOwner');
+    settings.add('offset: $offset');
+  }
+
+  String debugDescribeChildren(String prefix) => '';
 }
 
 /// A composited layer containing a [Picture]
@@ -88,6 +114,10 @@ class PictureLayer extends Layer {
     builder.addPicture(offset + layerOffset, picture, paintBounds);
   }
 
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('paintBounds: $paintBounds');
+  }
 }
 
 /// A layer that indicates to the compositor that it should display
@@ -113,7 +143,6 @@ class StatisticsLayer extends Layer {
     builder.addStatistics(optionsMask, paintBounds.shift(layerOffset));
     builder.setRasterizerTracingThreshold(rasterizerThreshold);
   }
-
 }
 
 
@@ -210,6 +239,23 @@ class ContainerLayer extends Layer {
     }
   }
 
+  String debugDescribeChildren(String prefix) {
+    String result = '$prefix \u2502\n';
+    if (_firstChild != null) {
+      Layer child = _firstChild;
+      int count = 1;
+      while (child != _lastChild) {
+        result += '${child.toStringDeep("$prefix \u251C\u2500child $count: ", "$prefix \u2502")}';
+        count += 1;
+        child = child._nextSibling;
+      }
+      if (child != null) {
+        assert(child == _lastChild);
+        result += '${child.toStringDeep("$prefix \u2514\u2500child $count: ", "$prefix  ")}';
+      }
+    }
+    return result;
+  }
 }
 
 /// A composite layer that clips its children using a rectangle
@@ -227,6 +273,10 @@ class ClipRectLayer extends ContainerLayer {
     builder.pop();
   }
 
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('clipRect: $clipRect');
+  }
 }
 
 /// A composite layer that clips its children using a rounded rectangle
@@ -248,6 +298,11 @@ class ClipRRectLayer extends ContainerLayer {
     builder.pop();
   }
 
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('bounds: $bounds');
+    settings.add('clipRRect: $clipRRect');
+  }
 }
 
 /// A composite layer that clips its children using a path
@@ -269,6 +324,11 @@ class ClipPathLayer extends ContainerLayer {
     builder.pop();
   }
 
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('bounds: $bounds');
+    settings.add('clipPath: $clipPath');
+  }
 }
 
 /// A composited layer that applies a transformation matrix to its children
@@ -285,6 +345,12 @@ class TransformLayer extends ContainerLayer {
     addChildrenToScene(builder, Offset.zero);
     builder.pop();
   }
+
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('transform:');
+    settings.addAll(debugDescribeTransform(transform));
+  }
 }
 
 /// A composited layer that makes its children partially transparent
@@ -306,4 +372,10 @@ class OpacityLayer extends ContainerLayer {
     addChildrenToScene(builder, offset + layerOffset);
     builder.pop();
   }
+
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('bounds: $bounds');
+    settings.add('alpha: $alpha');
+  }
 }

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

@@ -74,6 +74,10 @@ class PaintingContext {
     assert(child.needsPaint);
     child._layer ??= new ContainerLayer();
     child._layer.removeAllChildren();
+    assert(() {
+      child._layer.debugOwner = child.debugOwner ?? child.runtimeType;
+      return true;
+    });
     PaintingContext childContext = new PaintingContext._(child._layer, child.paintBounds);
     child._paintWithContext(childContext, Offset.zero);
     childContext._stopRecordingIfNeeded();
@@ -104,6 +108,10 @@ class PaintingContext {
     } else {
       assert(child._layer != null);
       child._layer.detach();
+      assert(() {
+        child._layer.debugOwner = child.debugOwner ?? child.runtimeType;
+        return true;
+      });
     }
     _appendLayer(child._layer, offset);
   }
@@ -435,7 +443,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// Override in subclasses with children and call the visitor for each child
   void visitChildren(RenderObjectVisitor visitor) { }
 
-  dynamic debugOwner = '';
+  dynamic debugOwner;
   void _debugReportException(String method, dynamic exception, StackTrace stack) {
     debugPrint('-- EXCEPTION --');
     debugPrint('The following exception was raised during $method():');
@@ -443,7 +451,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     debugPrint('Stack trace:');
     debugPrint('$stack');
     debugPrint('The following RenderObject was being processed when the exception was fired:\n${this}');
-    if (debugOwner != '')
+    if (debugOwner != null)
       debugPrint('That RenderObject had the following owner:\n$debugOwner');
     if (debugRenderingExceptionHandler != null)
       debugRenderingExceptionHandler(this, method, exception, stack);
@@ -1094,10 +1102,10 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// per string. Subclasses should override this to have their information
   /// included in toStringDeep().
   void debugDescribeSettings(List<String> settings) {
+    if (debugOwner != null)
+      settings.add('owner: $debugOwner');
     settings.add('parentData: $parentData');
     settings.add('constraints: $constraints');
-    if (debugOwner != '')
-      settings.add('owner: $debugOwner');
   }
 
   /// Returns a string describing the current node's descendants. Each line of

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

@@ -10,6 +10,7 @@ import 'package:flutter/gestures.dart';
 import 'package:vector_math/vector_math_64.dart';
 
 import 'box.dart';
+import 'debug.dart';
 import 'object.dart';
 
 export 'package:flutter/src/painting/box_painter.dart';
@@ -875,10 +876,8 @@ class RenderTransform extends RenderProxyBox {
 
   void debugDescribeSettings(List<String> settings) {
     super.debugDescribeSettings(settings);
-    List<String> matrix = _transform.toString().split('\n').map((String s) => '  $s').toList();
-    matrix.removeLast();
     settings.add('transform matrix:');
-    settings.addAll(matrix);
+    settings.addAll(debugDescribeTransform(_transform));
     settings.add('origin: $origin');
     settings.add('alignment: $alignment');
   }