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sky/sdk/lib/framework/rendering/paragraph.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:sky' as sky;
 import 'box.dart';
 import 'object.dart';
 
 class RenderInline extends RenderObject {
   String data;
 
   RenderInline(this.data);
 }
 
+// Unfortunately, using full precision floating point here causes bad layouts
+// because floating point math isn't associative. If we add and subtract
+// padding, for example, we'll get different values when we estimate sizes and
+// when we actually compute layout because the operations will end up associated
+// differently. To work around this problem for now, we round fractional pixel
+// values up to the nearest whole pixel value. The right long-term fix is to do
+// layout using fixed precision arithmetic.
+double _applyFloatingPointHack(double layoutValue) {
+  return layoutValue.ceilToDouble();
+}
+
 class RenderParagraph extends RenderBox {
 
   RenderParagraph({
     String text,
     Color color
   }) : _color = color {
     _layoutRoot.rootElement = _document.createElement('p');
     this.text = text;
   }
 
   final sky.Document _document = new sky.Document();
   final sky.LayoutRoot _layoutRoot = new sky.LayoutRoot();
 
   String get text => (_layoutRoot.rootElement.firstChild as sky.Text).data;
   void set text (String value) {
     _layoutRoot.rootElement.setChild(_document.createText(value));
     markNeedsLayout();
   }
 
   Color _color = const Color(0xFF000000);
   Color get color => _color;
   void set color (Color value) {
     if (_color != value) {
       _color = value;
       markNeedsPaint();
     }
   }
 
-  // We don't currently support this for RenderParagraph
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    assert(false);
-    return constraints.constrainWidth(0.0);
-  }
-
-  // We don't currently support this for RenderParagraph
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    assert(false);
-    return constraints.constrainWidth(0.0);
-  }
-
-  // We don't currently support this for RenderParagraph
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    assert(false);
-    return constraints.constrainHeight(0.0);
-  }
-
-  // We don't currently support this for RenderParagraph
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    assert(false);
-    return constraints.constrainHeight(0.0);
-  }
-
-  void performLayout() {
+  sky.Element _layout(BoxConstraints constraints) {
     _layoutRoot.maxWidth = constraints.maxWidth;
     _layoutRoot.minWidth = constraints.minWidth;
     _layoutRoot.minHeight = constraints.minHeight;
     _layoutRoot.maxHeight = constraints.maxHeight;
     _layoutRoot.layout();
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    _layout(constraints);
+    return constraints.constrainWidth(
+        _applyFloatingPointHack(_layoutRoot.rootElement.minContentWidth));
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    _layout(constraints);
+    return constraints.constrainWidth(
+        _applyFloatingPointHack(_layoutRoot.rootElement.maxContentWidth));
+  }
+
+  double _getIntrinsicHeight(BoxConstraints constraints) {
+    _layout(constraints);
+    return constraints.constrainHeight(
+        _applyFloatingPointHack(_layoutRoot.rootElement.height.ceilToDouble));
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    return _getIntrinsicHeight(constraints);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    return _getIntrinsicHeight(constraints);
+  }
+
+  void performLayout() {
+    _layout(constraints);
+    sky.Element root = _layoutRoot.rootElement;
     // rootElement.width always expands to fill, use maxContentWidth instead.
-    sky.Element root = _layoutRoot.rootElement;
-    size = constraints.constrain(new Size(root.maxContentWidth, root.height));
+    size = constraints.constrain(new Size(_applyFloatingPointHack(root.maxContentWidth),
+                                          _applyFloatingPointHack(root.height)));
   }
 
   void paint(RenderObjectDisplayList canvas) {
     // _layoutRoot.rootElement.style['color'] = 'rgba(' + ...color... + ')';
     _layoutRoot.paint(canvas);
   }
 
   // we should probably expose a way to do precise (inter-glpyh) hit testing
 
   String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}color: ${color}\n${prefix}text: ${text}\n';
 }