Object size on heap map hover.

runtime/bin/vmservice/client/lib/src/elements/heap_map.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library heap_map_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:math';
 import 'observatory_element.dart';
@@ skipping 25 matching lines @@
       _data.data.getRange(_dataIndex, _dataIndex + NUM_COLOR_COMPONENTS);
 
   // Returns the next pixel in row-major order.
   PixelReference next() => new PixelReference._fromDataIndex(
       _data, _dataIndex + NUM_COLOR_COMPONENTS);
 
   // The row-major index of this pixel.
   int get index => _dataIndex ~/ NUM_COLOR_COMPONENTS;
 }
 
+class ObjectInfo {
+  final address;
+  final size;
+  ObjectInfo(this.address, this.size);
+}
+
 @CustomTag('heap-map')
 class HeapMapElement extends ObservatoryElement {
   var _fragmentationCanvas;
   var _fragmentationData;
   var _pageHeight;
   var _classIdToColor = {};
   var _colorToClassId = {};
   var _classIdToName = {};
 
   static final _freeColor = [255, 255, 255, 255];
@@ skipping 46 matching lines @@
     // TODO(koda): Pick random hue, but fixed saturation and value.
     var rng = new Random(classId);
     return [rng.nextInt(128), rng.nextInt(128), rng.nextInt(128), 255];
   }
 
   String _classNameAt(Point<int> point) {
     var color = new PixelReference(_fragmentationData, point).color;
     return _classIdToName[_colorToClassId[_packColor(color)]];
   }
 
-  // TODO(koda): Find start of object.
-  int _addressAt(Point<int> point) {
+  ObjectInfo _objectAt(Point<int> point) {
     var pagePixels = _pageHeight * _fragmentationData.width;
     var index = new PixelReference(_fragmentationData, point).index;
     var pageIndex = index ~/ pagePixels;
     var pageOffset = index % pagePixels;
     var pages = fragmentation['pages'];
-    if (0 <= pageIndex && pageIndex < pages.length) {
-      return int.parse(pages[pageIndex]['object_start']) +
-           pageOffset * fragmentation['unit_size_bytes'];
-    } else {
-      return 0;
+    if (pageIndex < 0 || pageIndex >= pages.length) {
+      return null;
     }
+    // Scan the page to find start and size.
+    var page = pages[pageIndex];
+    var objects = page['objects'];
+    var offset = 0;
+    var size = 0;
+    for (var i = 0; i < objects.length; i += 2) {
+      size = objects[i];
+      offset += size;
+      if (offset > pageOffset) {
+        pageOffset = offset - size;
+        break;
+      }
+    }
+    return new ObjectInfo(int.parse(page['object_start']) +
+                          pageOffset * fragmentation['unit_size_bytes'],
+        size * fragmentation['unit_size_bytes']);
   }
 
   void _handleMouseMove(MouseEvent event) {
-    var addressString = '@ 0x${_addressAt(event.offset).toRadixString(16)}';
+    var info = _objectAt(event.offset);
+    var addressString = '${info.size}B @ 0x${info.address.toRadixString(16)}';
     var className = _classNameAt(event.offset);
     status = (className == '') ? '-' : '$className $addressString';
   }
   
   void _handleClick(MouseEvent event) {
-    var address = _addressAt(event.offset).toRadixString(16);
+    var address = _objectAt(event.offset).address.toRadixString(16);
     window.location.hash = "/${fragmentation.isolate.link}/address/$address";
   }
 
   void _updateFragmentationData() {
     if (fragmentation == null || _fragmentationCanvas == null) {
       return;
     }
     _updateClassList(
         fragmentation['class_list'], fragmentation['free_class_id']);
     var pages = fragmentation['pages'];
@@ skipping 54 matching lines @@
     }).whenComplete(done);
   }
 
   void fragmentationChanged(oldValue) {
     // Async, in case enteredView has not yet run (observed in JS version).
     new Future(() {
       _updateFragmentationData();
     });
   }
 }