Improve drawer performance

sky/sdk/lib/rendering/box.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 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/base/debug.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/rendering/object.dart';
@@ skipping 1231 matching lines @@
       Rect childBounds = child.parentData.position & child.size;
       if (childBounds.contains(position + -scrollOffset))
         child.hitTest(result, position: position + scrollOffset);
     }
   }
 
 }
 
 class RenderImage extends RenderBox {
 
-  RenderImage(sky.Image image, Size requestedSize)
-    : _image = image, _requestedSize = requestedSize;
+  RenderImage(sky.Image image, Size requestedSize, { sky.ColorFilter colorFilter })
+    : _image = image,
+      _requestedSize = requestedSize,
+      _colorFilter = colorFilter;
 
   sky.Image _image;
   sky.Image get image => _image;
   void set image (sky.Image value) {
     if (value == _image)
       return;
     _image = value;
     markNeedsPaint();
     if (_requestedSize.width == null || _requestedSize.height == null)
       markNeedsLayout();
   }
 
   Size _requestedSize;
   Size get requestedSize => _requestedSize;
   void set requestedSize (Size value) {
     if (value == null)
       value = const Size(null, null);
     if (value == _requestedSize)
       return;
     _requestedSize = value;
     markNeedsLayout();
   }
 
+  sky.ColorFilter _colorFilter;
+  sky.ColorFilter get colorFilter => _colorFilter;
+  void set colorFilter (sky.ColorFilter value) {
+    if (value == _colorFilter)
+      return;
+    _colorFilter = value;
+    _cachedPaint = null;
+    markNeedsPaint();
+  }
+
+  Paint _cachedPaint;
+  Paint get _paint {
+    if (_cachedPaint == null) {
+      _cachedPaint = new Paint();
+      if (colorFilter != null)
+        _cachedPaint.setColorFilter(colorFilter);
+    }
+    return _cachedPaint;
+  }
+
   Size _sizeForConstraints(BoxConstraints innerConstraints) {
     // If there's no image, we can't size ourselves automatically
     if (_image == null) {
       double width = requestedSize.width == null ? 0.0 : requestedSize.width;
       double height = requestedSize.height == null ? 0.0 : requestedSize.height;
       return constraints.constrain(new Size(width, height));
     }
 
     if (!innerConstraints.isTight) {
       // If neither height nor width are specified, use inherent image
@@ skipping 56 matching lines @@
       return;
     bool needsScale = size.width != _image.width || size.height != _image.height;
     if (needsScale) {
       double widthScale = size.width / _image.width;
       double heightScale = size.height / _image.height;
       canvas.save();
       canvas.translate(offset.dx, offset.dy);
       canvas.scale(widthScale, heightScale);
       offset = Offset.zero;
     }
-    canvas.drawImage(_image, offset.toPoint(), new Paint());
+    canvas.drawImage(_image, offset.toPoint(), _paint);
     if (needsScale)
       canvas.restore();
   }
 
   String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}dimensions: ${requestedSize}\n';
 }
 
 class RenderDecoratedBox extends RenderProxyBox {
 
   RenderDecoratedBox({
@@ skipping 304 matching lines @@
 
   void defaultPaint(PaintingCanvas canvas, Offset offset) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position + offset);
       child = child.parentData.nextSibling;
     }
   }
 }