Remove OverlayPainter mechanism (#4264)

We used to use this mechanism to paint scrollbars, but it's awkward. The
new approach to scrollbars is much cleaner. This mechanism has no other
clients, so we should remove it.

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

@@ -401,12 +401,10 @@ class RenderGrid extends RenderVirtualViewport<GridParentData> {
     int virtualChildBase: 0,
     int virtualChildCount,
     Offset paintOffset: Offset.zero,
-    RenderObjectPainter overlayPainter,
     LayoutCallback callback
   }) : _delegate = delegate, _virtualChildBase = virtualChildBase, super(
     virtualChildCount: virtualChildCount,
     paintOffset: paintOffset,
-    overlayPainter: overlayPainter,
     callback: callback
   ) {
     assert(delegate != null);

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

@@ -33,7 +33,6 @@ class RenderList extends RenderVirtualViewport<ListParentData> {
     Offset paintOffset: Offset.zero,
     Axis mainAxis: Axis.vertical,
     ViewportAnchor anchor: ViewportAnchor.start,
-    RenderObjectPainter overlayPainter,
     LayoutCallback callback
   }) : _itemExtent = itemExtent,
        _padding = padding,
@@ -42,7 +41,6 @@ class RenderList extends RenderVirtualViewport<ListParentData> {
          paintOffset: paintOffset,
          mainAxis: mainAxis,
          anchor: anchor,
-         overlayPainter: overlayPainter,
          callback: callback
        ) {
     addAll(children);

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

@@ -397,28 +397,6 @@ class PaintingContext {
   }
 }
 
-/// An encapsulation of a renderer and a paint() method.
-///
-/// A renderer may allow its paint() method to be augmented or redefined by
-/// providing a Painter. See for example overlayPainter in BlockViewport.
-abstract class RenderObjectPainter {
-  RenderObject get renderObject => _renderObject;
-  RenderObject _renderObject;
-
-  void attach(RenderObject renderObject) {
-    assert(_renderObject == null);
-    assert(renderObject != null);
-    _renderObject = renderObject;
-  }
-
-  void detach() {
-    assert(_renderObject != null);
-    _renderObject = null;
-  }
-
-  void paint(PaintingContext context, Offset offset);
-}
-
 /// An abstract set of layout constraints.
 ///
 /// Concrete layout models (such as box) will create concrete subclasses to

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

@@ -85,12 +85,10 @@ class RenderViewportBase extends RenderBox {
   RenderViewportBase(
     Offset paintOffset,
     Axis mainAxis,
-    ViewportAnchor anchor,
-    RenderObjectPainter overlayPainter
+    ViewportAnchor anchor
   ) : _paintOffset = paintOffset,
       _mainAxis = mainAxis,
-      _anchor = anchor,
-      _overlayPainter = overlayPainter {
+      _anchor = anchor {
     assert(paintOffset != null);
     assert(mainAxis != null);
     assert(_offsetIsSane(_paintOffset, mainAxis));
@@ -150,31 +148,6 @@ class RenderViewportBase extends RenderBox {
     markNeedsSemanticsUpdate();
   }
 
-  RenderObjectPainter get overlayPainter => _overlayPainter;
-  RenderObjectPainter _overlayPainter;
-  set overlayPainter(RenderObjectPainter value) {
-    if (_overlayPainter == value)
-      return;
-    if (attached)
-      _overlayPainter?.detach();
-    _overlayPainter = value;
-    if (attached)
-      _overlayPainter?.attach(this);
-    markNeedsPaint();
-  }
-
-  @override
-  void attach(PipelineOwner owner) {
-    super.attach(owner);
-    _overlayPainter?.attach(this);
-  }
-
-  @override
-  void detach() {
-    super.detach();
-    _overlayPainter?.detach();
-  }
-
   ViewportDimensions get dimensions => _dimensions;
   ViewportDimensions _dimensions = ViewportDimensions.zero;
   set dimensions(ViewportDimensions value) {
@@ -204,8 +177,6 @@ class RenderViewportBase extends RenderBox {
     description.add('paintOffset: $paintOffset');
     description.add('mainAxis: $mainAxis');
     description.add('anchor: $anchor');
-    if (overlayPainter != null)
-      description.add('overlay painter: $overlayPainter');
   }
 }
 
@@ -224,9 +195,8 @@ class RenderViewport extends RenderViewportBase with RenderObjectWithChildMixin<
     Offset paintOffset: Offset.zero,
     Axis mainAxis: Axis.vertical,
     ViewportAnchor anchor: ViewportAnchor.start,
-    RenderObjectPainter overlayPainter,
     this.onPaintOffsetUpdateNeeded
-  }) : super(paintOffset, mainAxis, anchor, overlayPainter) {
+  }) : super(paintOffset, mainAxis, anchor) {
     this.child = child;
   }
 
@@ -314,7 +284,6 @@ class RenderViewport extends RenderViewportBase with RenderObjectWithChildMixin<
 
       void paintContents(PaintingContext context, Offset offset) {
         context.paintChild(child, offset + effectivePaintOffset);
-        _overlayPainter?.paint(context, offset);
       }
 
       if (_shouldClipAtPaintOffset(effectivePaintOffset)) {
@@ -357,11 +326,10 @@ abstract class RenderVirtualViewport<T extends ContainerBoxParentDataMixin<Rende
     LayoutCallback callback,
     Offset paintOffset: Offset.zero,
     Axis mainAxis: Axis.vertical,
-    ViewportAnchor anchor: ViewportAnchor.start,
-    RenderObjectPainter overlayPainter
+    ViewportAnchor anchor: ViewportAnchor.start
   }) : _virtualChildCount = virtualChildCount,
        _callback = callback,
-       super(paintOffset, mainAxis, anchor, overlayPainter);
+       super(paintOffset, mainAxis, anchor);
 
   int get virtualChildCount => _virtualChildCount;
   int _virtualChildCount;
@@ -392,7 +360,6 @@ abstract class RenderVirtualViewport<T extends ContainerBoxParentDataMixin<Rende
 
   void _paintContents(PaintingContext context, Offset offset) {
     defaultPaint(context, offset + _effectivePaintOffset);
-    _overlayPainter?.paint(context, offset);
   }
 
   @override

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

@@ -42,7 +42,6 @@ export 'package:flutter/rendering.dart' show
     PointerUpEvent,
     PointerUpEventListener,
     RelativeRect,
-    RenderObjectPainter,
     ShaderCallback,
     SingleChildLayoutDelegate,
     TextOverflow,
@@ -1147,7 +1146,6 @@ class Viewport extends SingleChildRenderObjectWidget {
     this.paintOffset: Offset.zero,
     this.mainAxis: Axis.vertical,
     this.anchor: ViewportAnchor.start,
-    this.overlayPainter,
     this.onPaintOffsetUpdateNeeded,
     Widget child
   }) : super(key: key, child: child) {
@@ -1169,11 +1167,6 @@ class Viewport extends SingleChildRenderObjectWidget {
 
   final ViewportAnchor anchor;
 
-  /// Paints an overlay over the viewport.
-  ///
-  /// Often used to paint scroll bars.
-  final RenderObjectPainter overlayPainter;
-
   /// Called when the interior or exterior dimensions of the viewport change.
   final ViewportDimensionsChangeCallback onPaintOffsetUpdateNeeded;
 
@@ -1183,8 +1176,7 @@ class Viewport extends SingleChildRenderObjectWidget {
       paintOffset: paintOffset,
       mainAxis: mainAxis,
       anchor: anchor,
-      onPaintOffsetUpdateNeeded: onPaintOffsetUpdateNeeded,
-      overlayPainter: overlayPainter
+      onPaintOffsetUpdateNeeded: onPaintOffsetUpdateNeeded
     );
   }
 
@@ -1195,8 +1187,7 @@ class Viewport extends SingleChildRenderObjectWidget {
       ..mainAxis = mainAxis
       ..anchor = anchor
       ..paintOffset = paintOffset
-      ..onPaintOffsetUpdateNeeded = onPaintOffsetUpdateNeeded
-      ..overlayPainter = overlayPainter;
+      ..onPaintOffsetUpdateNeeded = onPaintOffsetUpdateNeeded;
   }
 }
 

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

@@ -318,8 +318,7 @@ class _VirtualPageViewport extends VirtualViewport {
     this.startOffset,
     this.mainAxis,
     this.anchor,
-    this.itemsWrap,
-    this.overlayPainter
+    this.itemsWrap
   ) {
     assert(mainAxis != null);
   }
@@ -330,7 +329,6 @@ class _VirtualPageViewport extends VirtualViewport {
   final Axis mainAxis;
   final ViewportAnchor anchor;
   final bool itemsWrap;
-  final RenderObjectPainter overlayPainter;
 
   @override
   RenderList createRenderObject(BuildContext context) => new RenderList();
@@ -374,8 +372,7 @@ class _VirtualPageViewportElement extends VirtualViewportElement {
   @override
   void updateRenderObject(_VirtualPageViewport oldWidget) {
     renderObject
-      ..mainAxis = widget.mainAxis
-      ..overlayPainter = widget.overlayPainter;
+      ..mainAxis = widget.mainAxis;
     super.updateRenderObject(oldWidget);
   }
 
@@ -442,14 +439,12 @@ class PageViewport extends _VirtualPageViewport with VirtualViewportFromIterable
     Axis mainAxis: Axis.vertical,
     ViewportAnchor anchor: ViewportAnchor.start,
     bool itemsWrap: false,
-    RenderObjectPainter overlayPainter,
     this.children
   }) : super(
     startOffset,
     mainAxis,
     anchor,
-    itemsWrap,
-    overlayPainter
+    itemsWrap
   );
 
   @override
@@ -461,15 +456,13 @@ class LazyPageViewport extends _VirtualPageViewport with VirtualViewportFromBuil
     double startOffset: 0.0,
     Axis mainAxis: Axis.vertical,
     ViewportAnchor anchor: ViewportAnchor.start,
-    RenderObjectPainter overlayPainter,
     this.itemCount,
     this.itemBuilder
   }) : super(
     startOffset,
     mainAxis,
     anchor,
-    false, // Don't support wrapping yet.
-    overlayPainter
+    false // Don't support wrapping yet.
   );
 
   @override

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

@@ -155,8 +155,7 @@ class _VirtualListViewport extends VirtualViewport {
     this.anchor,
     this.itemExtent,
     this.itemsWrap,
-    this.padding,
-    this.overlayPainter
+    this.padding
   ) {
     assert(mainAxis != null);
     assert(itemExtent != null);
@@ -169,7 +168,6 @@ class _VirtualListViewport extends VirtualViewport {
   final double itemExtent;
   final bool itemsWrap;
   final EdgeInsets padding;
-  final RenderObjectPainter overlayPainter;
 
   double get _leadingPadding {
     switch (mainAxis) {
@@ -237,8 +235,7 @@ class _VirtualListViewportElement extends VirtualViewportElement {
       ..mainAxis = widget.mainAxis
       ..anchor = widget.anchor
       ..itemExtent = widget.itemExtent
-      ..padding = widget.padding
-      ..overlayPainter = widget.overlayPainter;
+      ..padding = widget.padding;
     super.updateRenderObject(oldWidget);
   }
 
@@ -320,7 +317,6 @@ class ListViewport extends _VirtualListViewport with VirtualViewportFromIterable
     double itemExtent,
     bool itemsWrap: false,
     EdgeInsets padding,
-    RenderObjectPainter overlayPainter,
     this.children
   }) : super(
     onExtentsChanged,
@@ -329,8 +325,7 @@ class ListViewport extends _VirtualListViewport with VirtualViewportFromIterable
     anchor,
     itemExtent,
     itemsWrap,
-    padding,
-    overlayPainter
+    padding
   );
 
   @override
@@ -486,7 +481,6 @@ class LazyListViewport extends _VirtualListViewport with VirtualViewportFromBuil
     ViewportAnchor anchor: ViewportAnchor.start,
     double itemExtent,
     EdgeInsets padding,
-    RenderObjectPainter overlayPainter,
     this.itemCount,
     this.itemBuilder
   }) : super(
@@ -496,8 +490,7 @@ class LazyListViewport extends _VirtualListViewport with VirtualViewportFromBuil
     anchor,
     itemExtent,
     false, // Don't support wrapping yet.
-    padding,
-    overlayPainter
+    padding
   );
 
   @override

packages/flutter/test/rendering/list_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/rendering.dart';
-import 'package:test/test.dart';
-
-import 'rendering_tester.dart';
-
-class TestBlockPainter extends RenderObjectPainter {
-  @override
-  void paint(PaintingContext context, Offset offset) { }
-}
-
-void main() {
-  test('overlay painters can attach and detach', () {
-    TestBlockPainter first = new TestBlockPainter();
-    TestBlockPainter second = new TestBlockPainter();
-    RenderList list = new RenderList(overlayPainter: first);
-
-    // The first painter isn't attached because we haven't attached block.
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, isNull);
-
-    list.overlayPainter = second;
-
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, isNull);
-
-    layout(list);
-
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, equals(list));
-
-    list.overlayPainter = first;
-
-    expect(first.renderObject, equals(list));
-    expect(second.renderObject, isNull);
-  });
-}