Do not apply the canvas bounds as a cull rectangle when recording a Skia picture (#14027)

The picture may need to draw outside the bounds (specifically for shadows)

Fixes https://github.com/flutter/flutter/issues/12618

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

@@ -59,25 +59,19 @@ typedef void PaintingContextCallback(PaintingContext context, Offset offset);
 /// New [PaintingContext] objects are created automatically when using
 /// [PaintingContext.repaintCompositedChild] and [pushLayer].
 class PaintingContext {
-  PaintingContext._(this._containerLayer, this.canvasBounds)
+  PaintingContext._(this._containerLayer, this.estimatedBounds)
     : assert(_containerLayer != null),
-      assert(canvasBounds != null);
+      assert(estimatedBounds != null);
 
   final ContainerLayer _containerLayer;
 
-  /// The bounds within which the painting context's [canvas] will record
-  /// painting commands.
+  /// An estimate of the bounds within which the painting context's [canvas]
+  /// will record painting commands.  This can be useful for debugging.
   ///
-  /// A render object provided with this [PaintingContext] (e.g. in its
-  /// [RenderObject.paint] method) is permitted to paint outside the region that
-  /// the render object occupies during layout, but is not permitted to paint
-  /// outside these canvas paints bounds. These paint bounds are used to
-  /// construct memory-efficient composited layers, which means attempting to
-  /// paint outside these bounds can attempt to write to pixels that do not
-  /// exist in the composited layer.
+  /// The canvas will allow painting outside these bounds.
   ///
-  /// The [canvasBounds] rectangle is in the [canvas] coordinate system.
-  final Rect canvasBounds;
+  /// The [estimatedBounds] rectangle is in the [canvas] coordinate system.
+  final Rect estimatedBounds;
 
   /// Repaint the given render object.
   ///
@@ -200,8 +194,6 @@ class PaintingContext {
   /// The current canvas can change whenever you paint a child using this
   /// context, which means it's fragile to hold a reference to the canvas
   /// returned by this getter.
-  ///
-  /// Only calls within the [canvasBounds] will be recorded.
   Canvas get canvas {
     if (_canvas == null)
       _startRecording();
@@ -210,9 +202,9 @@ class PaintingContext {
 
   void _startRecording() {
     assert(!_isRecording);
-    _currentLayer = new PictureLayer(canvasBounds);
+    _currentLayer = new PictureLayer(estimatedBounds);
     _recorder = new ui.PictureRecorder();
-    _canvas = new Canvas(_recorder, canvasBounds);
+    _canvas = new Canvas(_recorder);
     _containerLayer.append(_currentLayer);
   }
 
@@ -225,14 +217,14 @@ class PaintingContext {
           ..style = PaintingStyle.stroke
           ..strokeWidth = 6.0
           ..color = debugCurrentRepaintColor.toColor();
-        canvas.drawRect(canvasBounds.deflate(3.0), paint);
+        canvas.drawRect(estimatedBounds.deflate(3.0), paint);
       }
       if (debugPaintLayerBordersEnabled) {
         final Paint paint = new Paint()
           ..style = PaintingStyle.stroke
           ..strokeWidth = 1.0
           ..color = const Color(0xFFFF9800);
-        canvas.drawRect(canvasBounds, paint);
+        canvas.drawRect(estimatedBounds, paint);
       }
       return true;
     }());
@@ -284,9 +276,9 @@ class PaintingContext {
   }
 
   /// Appends the given layer to the recording, and calls the `painter` callback
-  /// with that layer, providing the `childPaintBounds` as the paint bounds of
-  /// the child. Canvas recording commands are not guaranteed to be stored
-  /// outside of the paint bounds.
+  /// with that layer, providing the `childPaintBounds` as the estimated paint
+  /// bounds of the child.  The `childPaintBounds` can be used for debugging but
+  /// have no effect on painting.
   ///
   /// The given layer must be an unattached orphan. (Providing a newly created
   /// object, rather than reusing an existing layer, satisfies that
@@ -309,7 +301,7 @@ class PaintingContext {
     assert(painter != null);
     _stopRecordingIfNeeded();
     _appendLayer(childLayer);
-    final PaintingContext childContext = new PaintingContext._(childLayer, childPaintBounds ?? canvasBounds);
+    final PaintingContext childContext = new PaintingContext._(childLayer, childPaintBounds ?? estimatedBounds);
     painter(childContext, offset);
     childContext._stopRecordingIfNeeded();
   }
@@ -413,7 +405,7 @@ class PaintingContext {
         new TransformLayer(transform: effectiveTransform),
         painter,
         offset,
-        childPaintBounds: MatrixUtils.inverseTransformRect(effectiveTransform, canvasBounds),
+        childPaintBounds: MatrixUtils.inverseTransformRect(effectiveTransform, estimatedBounds),
       );
     } else {
       canvas
@@ -444,7 +436,7 @@ class PaintingContext {
   }
 
   @override
-  String toString() => '$runtimeType#$hashCode(layer: $_containerLayer, canvas bounds: $canvasBounds)';
+  String toString() => '$runtimeType#$hashCode(layer: $_containerLayer, canvas bounds: $estimatedBounds)';
 }
 
 /// An abstract set of layout constraints.
@@ -2037,17 +2029,8 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
     }());
   }
 
-  /// The bounds within which this render object will paint.
-  ///
-  /// A render object and its descendants are permitted to paint outside the
-  /// region it occupies during layout, but they are not permitted to paint
-  /// outside these paints bounds. These paint bounds are used to construct
-  /// memory-efficient composited layers, which means attempting to paint
-  /// outside these bounds can attempt to write to pixels that do not exist in
-  /// this render object's composited layer.
-  ///
-  /// The [paintBounds] are only actually enforced when the render object is a
-  /// repaint boundary; see [isRepaintBoundary].
+  /// An estimate of the bounds within which this render object will paint.
+  /// Useful for debugging flags such as [debugPaintLayerBordersEnabled].
   Rect get paintBounds;
 
   /// Override this method to paint debugging information.