diff --git a/packages/flutter/lib/src/rendering/layer.dart b/packages/flutter/lib/src/rendering/layer.dart
index 279ddcbae60..d2e9082fa6c 100644
--- a/packages/flutter/lib/src/rendering/layer.dart
+++ b/packages/flutter/lib/src/rendering/layer.dart
@@ -372,11 +372,7 @@ class TransformLayer extends ContainerLayer {
 
 /// A composited layer that makes its children partially transparent
 class OpacityLayer extends ContainerLayer {
-  OpacityLayer({ Offset offset: Offset.zero, this.bounds, this.alpha }) : super(offset: offset);
-
-  /// Unused
-  Rect bounds;
-  // TODO(abarth): Remove.
+  OpacityLayer({ Offset offset: Offset.zero, this.alpha }) : super(offset: offset);
 
   /// The amount to multiply into the alpha channel
   ///
@@ -386,14 +382,13 @@ class OpacityLayer extends ContainerLayer {
 
   void addToScene(ui.SceneBuilder builder, Offset layerOffset) {
     Offset childOffset = offset + layerOffset;
-    builder.pushOpacity(alpha, bounds?.shift(childOffset));
+    builder.pushOpacity(alpha, null);
     addChildrenToScene(builder, childOffset);
     builder.pop();
   }
 
   void debugDescribeSettings(List<String> settings) {
     super.debugDescribeSettings(settings);
-    settings.add('bounds: $bounds');
     settings.add('alpha: $alpha');
   }
 }
diff --git a/packages/flutter/lib/src/rendering/object.dart b/packages/flutter/lib/src/rendering/object.dart
index 6877a087815..fb16aa0ebe7 100644
--- a/packages/flutter/lib/src/rendering/object.dart
+++ b/packages/flutter/lib/src/rendering/object.dart
@@ -285,31 +285,17 @@ class PaintingContext {
     }
   }
 
-  static Paint _getPaintForAlpha(int alpha) {
-    return new Paint()
-      ..color = new Color.fromARGB(alpha, 0, 0, 0)
-      ..transferMode = TransferMode.srcOver
-      ..isAntiAlias = false;
-  }
-
   /// Push an opacity layer.
   ///
   /// This function will call painter synchronously with a painting context that
   /// will be blended with the given alpha value.
-  void pushOpacity(bool needsCompositing, Offset offset, Rect bounds, int alpha, PaintingContextCallback painter) {
-    if (needsCompositing) {
-      _stopRecordingIfNeeded();
-      OpacityLayer opacityLayer = new OpacityLayer(bounds: bounds, alpha: alpha);
-      _appendLayer(opacityLayer, offset);
-      PaintingContext childContext = new PaintingContext._(opacityLayer, _paintBounds);
-      painter(childContext, Offset.zero);
-      childContext._stopRecordingIfNeeded();
-    } else {
-      // TODO(abarth): pushOpacity should require bounds.
-      canvas.saveLayer(bounds?.shift(offset), _getPaintForAlpha(alpha));
-      painter(this, offset);
-      canvas.restore();
-    }
+  void pushOpacity(Offset offset, int alpha, PaintingContextCallback painter) {
+    _stopRecordingIfNeeded();
+    OpacityLayer opacityLayer = new OpacityLayer(alpha: alpha);
+    _appendLayer(opacityLayer, offset);
+    PaintingContext childContext = new PaintingContext._(opacityLayer, _paintBounds);
+    painter(childContext, Offset.zero);
+    childContext._stopRecordingIfNeeded();
   }
 
   static Paint _getPaintForShaderMask(Rect bounds,
@@ -435,7 +421,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     setupParentData(child);
     super.adoptChild(child);
     markNeedsLayout();
-    _markNeedsCompositingBitsUpdate();
+    markNeedsCompositingBitsUpdate();
   }
 
   /// Called by subclasses when they decide a render object is no longer a child.
@@ -451,7 +437,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     child.parentData = null;
     super.dropChild(child);
     markNeedsLayout();
-    _markNeedsCompositingBitsUpdate();
+    markNeedsCompositingBitsUpdate();
   }
 
   /// Calls visitor for each immediate child of this render object.
@@ -854,7 +840,8 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// creates at least one composited layer. For example, videos should return
   /// true if they use hardware decoders.
   ///
-  /// Warning: This getter must not change value over the lifetime of this object.
+  /// You must call markNeedsCompositingBitsUpdate() if the value of this
+  /// getter changes.
   bool get alwaysNeedsCompositing => false;
 
   ContainerLayer _layer;
@@ -880,7 +867,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// This method does not schedule a rendering frame, because since
   /// it cannot be the case that _only_ the compositing bits changed,
   /// something else will have scheduled a frame for us.
-  void _markNeedsCompositingBitsUpdate() {
+  void markNeedsCompositingBitsUpdate() {
     if (_needsCompositingBitsUpdate)
       return;
     _needsCompositingBitsUpdate = true;
@@ -889,7 +876,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
       if (parent._needsCompositingBitsUpdate)
         return;
       if (!isRepaintBoundary && !parent.isRepaintBoundary) {
-        parent._markNeedsCompositingBitsUpdate();
+        parent.markNeedsCompositingBitsUpdate();
         return;
       }
     }
diff --git a/packages/flutter/lib/src/rendering/proxy_box.dart b/packages/flutter/lib/src/rendering/proxy_box.dart
index a24a69dacca..abf1d0eab51 100644
--- a/packages/flutter/lib/src/rendering/proxy_box.dart
+++ b/packages/flutter/lib/src/rendering/proxy_box.dart
@@ -525,6 +525,8 @@ class RenderIntrinsicHeight extends RenderProxyBox {
 
 }
 
+int _getAlphaFromOpacity(double opacity) => (opacity * 255).round();
+
 /// Makes its child partially transparent.
 ///
 /// This class paints its child into an intermediate buffer and then blends the
@@ -534,10 +536,12 @@ class RenderIntrinsicHeight extends RenderProxyBox {
 /// into an intermediate buffer.
 class RenderOpacity extends RenderProxyBox {
   RenderOpacity({ RenderBox child, double opacity })
-    : this._opacity = opacity, super(child) {
+    : _opacity = opacity, _alpha = _getAlphaFromOpacity(opacity), super(child) {
     assert(opacity >= 0.0 && opacity <= 1.0);
   }
 
+  bool get alwaysNeedsCompositing => _alpha != 0 && _alpha != 255;
+
   /// The fraction to scale the child's alpha value.
   ///
   /// An opacity of 1.0 is fully opaque. An opacity of 0.0 is fully transparent
@@ -550,22 +554,23 @@ class RenderOpacity extends RenderProxyBox {
     if (_opacity == newOpacity)
       return;
     _opacity = newOpacity;
+    _alpha = _getAlphaFromOpacity(_opacity);
+    markNeedsCompositingBitsUpdate();
     markNeedsPaint();
   }
 
-  int get _alpha => (_opacity * 255).round();
+  int _alpha;
 
   void paint(PaintingContext context, Offset offset) {
     if (child != null) {
-      int a = _alpha;
-      if (a == 0)
+      if (_alpha == 0)
         return;
-      if (a == 255) {
+      if (_alpha == 255) {
         context.paintChild(child, offset);
         return;
       }
-      // TODO(abarth): We should pass bounds here.
-      context.pushOpacity(needsCompositing, offset, null, a, super.paint);
+      assert(needsCompositing);
+      context.pushOpacity(offset, _alpha, super.paint);
     }
   }