Sky support for flexbox justify content

sky/sdk/lib/framework/rendering/flex.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 'box.dart';
 import 'object.dart';
 
 class FlexBoxParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
   int flex;
   void merge(FlexBoxParentData other) {
     if (other.flex != null)
       flex = other.flex;
     super.merge(other);
   }
   String toString() => '${super.toString()}; flex=$flex';
 }
 
 enum FlexDirection { horizontal, vertical }
+enum FlexJustifyContent {
+  flexStart,
+  flexEnd,
+  center,
+  spaceBetween,
+  spaceAround,
+}
 
 class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, FlexBoxParentData>,
                                         RenderBoxContainerDefaultsMixin<RenderBox, FlexBoxParentData> {
   // lays out RenderBox children using flexible layout
 
   RenderFlex({
-    FlexDirection direction: FlexDirection.horizontal
-  }) : _direction = direction;
+    FlexDirection direction: FlexDirection.horizontal,
+    FlexJustifyContent justifyContent: FlexJustifyContent.flexStart
+  }) : _direction = direction, _justifyContent = justifyContent;
 
   FlexDirection _direction;
   FlexDirection get direction => _direction;
   void set direction (FlexDirection value) {
     if (_direction != value) {
       _direction = value;
       markNeedsLayout();
     }
   }
 
+  FlexJustifyContent _justifyContent;
+  FlexJustifyContent get justifyContent => _justifyContent;
+  void set justifyContent (FlexJustifyContent value) {
+    if (_justifyContent != value) {
+      _justifyContent = value;
+      markNeedsLayout();
+    }
+  }
+
   void setParentData(RenderBox child) {
     if (child.parentData is! FlexBoxParentData)
       child.parentData = new FlexBoxParentData();
   }
 
   bool get sizedByParent => true;
   void performResize() {
     size = constraints.constrain(new Size(constraints.maxWidth, constraints.maxHeight));
     assert(size.height < double.INFINITY);
     assert(size.width < double.INFINITY);
   }
 
   int _getFlex(RenderBox child) {
     assert(child.parentData is FlexBoxParentData);
     return child.parentData.flex != null ? child.parentData.flex : 0;
   }
 
   void performLayout() {
     // Based on http://www.w3.org/TR/css-flexbox-1/ Section 9.7 Resolving Flexible Lengths
     // Steps 1-3. Determine used flex factor, size inflexible items, calculate free space
     int totalFlex = 0;
+    int totalChildren = 0;
     assert(constraints != null);
     double freeSpace = (_direction == FlexDirection.horizontal) ? constraints.maxWidth : constraints.maxHeight;
     RenderBox child = firstChild;
     while (child != null) {
+      totalChildren++;
       int flex = _getFlex(child);
       if (flex > 0) {
         totalFlex += child.parentData.flex;
       } else {
         BoxConstraints innerConstraints = new BoxConstraints(maxHeight: constraints.maxHeight,
                                                              maxWidth: constraints.maxWidth);
         child.layout(innerConstraints, parentUsesSize: true);
         freeSpace -= (_direction == FlexDirection.horizontal) ? child.size.width : child.size.height;
       }
       child = child.parentData.nextSibling;
@@ skipping 14 matching lines @@
                                                   minWidth: spaceForChild,
                                                   maxWidth: spaceForChild);
             break;
           case FlexDirection.vertical:
             innerConstraints = new BoxConstraints(minHeight: spaceForChild,
                                                   maxHeight: spaceForChild,
                                                   maxWidth: constraints.maxWidth);
             break;
         }
         child.layout(innerConstraints, parentUsesSize: true);
-      }
-
-      // For now, center the flex items in the cross direction
-      switch (_direction) {
-        case FlexDirection.horizontal:
-          child.parentData.position = new Point(usedSpace, size.height / 2.0 - child.size.height / 2.0);
-          usedSpace += child.size.width;
-          break;
-        case FlexDirection.vertical:
-          child.parentData.position = new Point(size.width / 2.0 - child.size.width / 2.0, usedSpace);
-          usedSpace += child.size.height;
-          break;
+        usedSpace += _direction == FlexDirection.horizontal ? child.size.width : child.size.height;
       }
       child = child.parentData.nextSibling;
     }
+
+    // Section 8.2: Axis Alignment using the justify-content property
+    double remainingSpace = math.max(0.0, freeSpace - usedSpace);
+    double leadingSpace;
+    double betweenSpace;
+    child = firstChild;
+    switch (_justifyContent) {
+      case FlexJustifyContent.flexStart:
+        leadingSpace = 0.0;
+        betweenSpace = 0.0;
+        break;
+      case FlexJustifyContent.flexEnd:
+        leadingSpace = remainingSpace;
+        betweenSpace = 0.0;
+        break;
+      case FlexJustifyContent.center:
+        leadingSpace = remainingSpace / 2.0;
+        betweenSpace = 0.0;
+        break;
+      case FlexJustifyContent.spaceBetween:
+        leadingSpace = 0.0;
+        betweenSpace = totalChildren > 1 ? remainingSpace / (totalChildren - 1) : 0.0;
+        break;
+      case FlexJustifyContent.spaceAround:
+        betweenSpace = totalChildren > 0 ? remainingSpace / totalChildren : 0.0;
+        leadingSpace = betweenSpace / 2.0;
+        break;
+    }
+
+    // Position elements. For now, center the flex items in the cross direction
+    double mainDimPosition = leadingSpace;
+    child = firstChild;
+    while (child != null) {
+      switch (_direction) {
+        case FlexDirection.horizontal:
+          child.parentData.position = new Point(mainDimPosition, size.height / 2.0 - child.size.height / 2.0);
+          mainDimPosition += child.size.width;
+          break;
+        case FlexDirection.vertical:
+          child.parentData.position = new Point(size.width / 2.0 - child.size.width / 2.0, mainDimPosition);
+          mainDimPosition += child.size.height;
+          break;
+      }
+      mainDimPosition += betweenSpace;
+      child = child.parentData.nextSibling;
+    }
   }
 
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(RenderObjectDisplayList canvas) {
     defaultPaint(canvas);
   }
 }