RenderBox should use Offset for child offset

Previously we used Position, which makes it harder to accumulate offsets
when walking the render tree.

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -111,8 +111,8 @@ class _ModalBottomSheetLayout extends OneChildLayoutDelegate {
     );
   }
 
-  Point getPositionForChild(Size size, Size childSize) {
-    return new Point(0.0, size.height - childSize.height * progress);
+  Offset getPositionForChild(Size size, Size childSize) {
+    return new Offset(0.0, size.height - childSize.height * progress);
   }
 
   bool shouldRelayout(_ModalBottomSheetLayout oldDelegate) {

packages/flutter/lib/src/material/scaffold.dart

@@ -44,14 +44,14 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
 
     if (isChild(_Child.toolBar)) {
       toolBarSize = layoutChild(_Child.toolBar, toolBarConstraints);
-      positionChild(_Child.toolBar, Point.origin);
+      positionChild(_Child.toolBar, Offset.zero);
     }
 
     if (isChild(_Child.body)) {
       final double bodyHeight = size.height - toolBarSize.height;
       final BoxConstraints bodyConstraints = toolBarConstraints.tightenHeight(bodyHeight);
       layoutChild(_Child.body, bodyConstraints);
-      positionChild(_Child.body, new Point(0.0, toolBarSize.height));
+      positionChild(_Child.body, new Offset(0.0, toolBarSize.height));
     }
 
     // The BottomSheet and the SnackBar are anchored to the bottom of the parent,
@@ -69,12 +69,12 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
 
     if (isChild(_Child.bottomSheet)) {
       bottomSheetSize = layoutChild(_Child.bottomSheet, fullWidthConstraints);
-      positionChild(_Child.bottomSheet, new Point((size.width - bottomSheetSize.width) / 2.0, size.height - bottomSheetSize.height));
+      positionChild(_Child.bottomSheet, new Offset((size.width - bottomSheetSize.width) / 2.0, size.height - bottomSheetSize.height));
     }
 
     if (isChild(_Child.snackBar)) {
       snackBarSize = layoutChild(_Child.snackBar, fullWidthConstraints);
-      positionChild(_Child.snackBar, new Point(0.0, size.height - snackBarSize.height));
+      positionChild(_Child.snackBar, new Offset(0.0, size.height - snackBarSize.height));
     }
 
     if (isChild(_Child.floatingActionButton)) {
@@ -85,12 +85,12 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
         fabY = math.min(fabY, size.height - snackBarSize.height - fabSize.height - _kFloatingActionButtonMargin);
       if (bottomSheetSize.height > 0.0)
         fabY = math.min(fabY, size.height - bottomSheetSize.height - fabSize.height / 2.0);
-      positionChild(_Child.floatingActionButton, new Point(fabX, fabY));
+      positionChild(_Child.floatingActionButton, new Offset(fabX, fabY));
     }
 
     if (isChild(_Child.drawer)) {
       layoutChild(_Child.drawer, looseConstraints);
-      positionChild(_Child.drawer, Point.origin);
+      positionChild(_Child.drawer, Offset.zero);
     }
   }
 }

packages/flutter/lib/src/material/tabs.dart

@@ -141,7 +141,7 @@ class _RenderTabBar extends RenderBox with
     while (child != null) {
       child.layout(tabConstraints);
       final _TabBarParentData childParentData = child.parentData;
-      childParentData.position = new Point(x, 0.0);
+      childParentData.offset = new Offset(x, 0.0);
       x += tabWidth;
       child = childParentData.nextSibling;
     }
@@ -159,7 +159,7 @@ class _RenderTabBar extends RenderBox with
     while (child != null) {
       child.layout(tabConstraints, parentUsesSize: true);
       final _TabBarParentData childParentData = child.parentData;
-      childParentData.position = new Point(x, 0.0);
+      childParentData.offset = new Offset(x, 0.0);
       x += child.size.width;
       child = childParentData.nextSibling;
     }
@@ -226,7 +226,7 @@ class _RenderTabBar extends RenderBox with
     final Size size = new Size(selectedTab.size.width, _kTabIndicatorHeight);
     final _TabBarParentData selectedTabParentData = selectedTab.parentData;
     final Point point = new Point(
-      selectedTabParentData.position.x,
+      selectedTabParentData.offset.dx,
       _tabBarHeight - _kTabIndicatorHeight
     );
     canvas.drawRect((point + offset) & size, new Paint()..color = indicatorColor);

packages/flutter/lib/src/rendering/auto_layout.dart

@@ -113,7 +113,7 @@ class AutoLayoutParentData extends ContainerBoxParentDataMixin<RenderBox> with _
       height: _bottomEdge.value - _topEdge.value
     );
     _renderBox.layout(size);
-    position = new Point(_leftEdge.value, _topEdge.value);
+    offset = new Offset(_leftEdge.value, _topEdge.value);
   }
 
   List<al.Constraint> _constructImplicitConstraints() {

packages/flutter/lib/src/rendering/block.dart

@@ -96,8 +96,8 @@ abstract class RenderBlockBase extends RenderBox with ContainerRenderObjectMixin
       return minExtent;
     BoxParentData parentData = child.parentData;
     return isVertical ?
-        math.max(minExtent, parentData.position.y + child.size.height) :
-        math.max(minExtent, parentData.position.x + child.size.width);
+        math.max(minExtent, parentData.offset.dy + child.size.height) :
+        math.max(minExtent, parentData.offset.dx + child.size.width);
   }
 
   void performLayout() {
@@ -107,7 +107,7 @@ abstract class RenderBlockBase extends RenderBox with ContainerRenderObjectMixin
     while (child != null) {
       child.layout(innerConstraints, parentUsesSize: true);
       final BlockParentData childParentData = child.parentData;
-      childParentData.position = isVertical ? new Point(0.0, position) : new Point(position, 0.0);
+      childParentData.offset = isVertical ? new Offset(0.0, position) : new Offset(position, 0.0);
       position += isVertical ? child.size.height : child.size.width;
       assert(child.parentData == childParentData);
       child = childParentData.nextSibling;

packages/flutter/lib/src/rendering/box.dart

@@ -316,17 +316,15 @@ class BoxHitTestEntry extends HitTestEntry {
 
 /// Parent data used by [RenderBox] and its subclasses.
 class BoxParentData extends ParentData {
-  // TODO(abarth): Switch to using an Offset rather than a Point here. This
-  //               value is really the offset from the parent.
-  Point _position = Point.origin;
-  /// The point at which to paint the child in the parent's coordinate system
-  Point get position => _position;
-  void set position(Point value) {
+  /// The offset at which to paint the child in the parent's coordinate system
+  Offset get offset => _offset;
+  Offset _offset = Offset.zero;
+  void set offset(Offset value) {
     assert(RenderObject.debugDoingLayout);
-    _position = value;
+    _offset = value;
   }
-  Offset get offset => _position.toOffset();
-  String toString() => 'position=$position';
+
+  String toString() => 'offset=$offset';
 }
 
 /// Abstract ParentData subclass for RenderBox subclasses that want the
@@ -631,8 +629,8 @@ abstract class RenderBox extends RenderObject {
   void applyPaintTransform(RenderObject child, Matrix4 transform) {
     assert(child.parent == this);
     BoxParentData childParentData = child.parentData;
-    Point position = childParentData.position;
-    transform.translate(position.x, position.y);
+    Offset offset = childParentData.offset;
+    transform.translate(offset.dx, offset.dy);
   }
 
   /// Convert the given point from the global coodinate system to the local
@@ -766,7 +764,7 @@ abstract class RenderBoxContainerDefaultsMixin<ChildType extends RenderBox, Pare
       final ParentDataType childParentData = child.parentData;
       double result = child.getDistanceToActualBaseline(baseline);
       if (result != null)
-        return result + childParentData.position.y;
+        return result + childParentData.offset.dy;
       child = childParentData.nextSibling;
     }
     return null;
@@ -784,7 +782,7 @@ abstract class RenderBoxContainerDefaultsMixin<ChildType extends RenderBox, Pare
       final ParentDataType childParentData = child.parentData;
       double candidate = child.getDistanceToActualBaseline(baseline);
       if (candidate != null) {
-        candidate += childParentData.position.y;
+        candidate += childParentData.offset.dy;
         if (result != null)
           result = math.min(result, candidate);
         else
@@ -804,8 +802,8 @@ abstract class RenderBoxContainerDefaultsMixin<ChildType extends RenderBox, Pare
     ChildType child = lastChild;
     while (child != null) {
       final ParentDataType childParentData = child.parentData;
-      Point transformed = new Point(position.x - childParentData.position.x,
-                                    position.y - childParentData.position.y);
+      Point transformed = new Point(position.x - childParentData.offset.dx,
+                                    position.y - childParentData.offset.dy);
       if (child.hitTest(result, position: transformed))
         return true;
       child = childParentData.previousSibling;

packages/flutter/lib/src/rendering/custom_layout.dart

@@ -47,11 +47,11 @@ abstract class MultiChildLayoutDelegate {
   }
 
   /// Specify the child's origin relative to this origin.
-  void positionChild(Object childId, Point position) {
+  void positionChild(Object childId, Offset offset) {
     final RenderBox child = _idToChild[childId];
     assert(child != null);
     final MultiChildLayoutParentData childParentData = child.parentData;
-    childParentData.position = position;
+    childParentData.offset = offset;
   }
 
   void _callPerformLayout(Size size, BoxConstraints constraints, RenderBox firstChild) {

packages/flutter/lib/src/rendering/flex.dart

@@ -530,10 +530,10 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
       }
       switch (_direction) {
         case FlexDirection.horizontal:
-          childParentData.position = new Point(childMainPosition, childCrossPosition);
+          childParentData.offset = new Offset(childMainPosition, childCrossPosition);
           break;
         case FlexDirection.vertical:
-          childParentData.position = new Point(childCrossPosition, childMainPosition);
+          childParentData.offset = new Offset(childCrossPosition, childMainPosition);
           break;
       }
       childMainPosition += _getMainSize(child) + betweenSpace;

packages/flutter/lib/src/rendering/grid.dart

@@ -125,7 +125,7 @@ class RenderGrid extends RenderBox with ContainerRenderObjectMixin<RenderBox, Gr
       double x = (column + 1) * metrics.childPadding + (column * metrics.childSize.width);
       double y = (row + 1) * metrics.childPadding + (row * metrics.childSize.height);
       final GridParentData childParentData = child.parentData;
-      childParentData.position = new Point(x, y);
+      childParentData.offset = new Offset(x, y);
 
       column += 1;
       if (column >= metrics.childrenPerRow) {

packages/flutter/lib/src/rendering/shifted_box.dart

@@ -49,7 +49,7 @@ abstract class RenderShiftedBox extends RenderBox with RenderObjectWithChildMixi
       result = child.getDistanceToActualBaseline(baseline);
       final BoxParentData childParentData = child.parentData;
       if (result != null)
-        result += childParentData.position.y;
+        result += childParentData.offset.dy;
     } else {
       result = super.computeDistanceToActualBaseline(baseline);
     }
@@ -66,8 +66,8 @@ abstract class RenderShiftedBox extends RenderBox with RenderObjectWithChildMixi
   bool hitTestChildren(HitTestResult result, { Point position }) {
     if (child != null) {
       final BoxParentData childParentData = child.parentData;
-      final Point childPosition = new Point(position.x - childParentData.position.x,
-                                            position.y - childParentData.position.y);
+      final Point childPosition = new Point(position.x - childParentData.offset.dx,
+                                            position.y - childParentData.offset.dy);
       return child.hitTest(result, position: childPosition);
     }
     return false;
@@ -146,7 +146,7 @@ class RenderPadding extends RenderShiftedBox {
     BoxConstraints innerConstraints = constraints.deflate(padding);
     child.layout(innerConstraints, parentUsesSize: true);
     final BoxParentData childParentData = child.parentData;
-    childParentData.position = new Point(padding.left, padding.top);
+    childParentData.offset = new Offset(padding.left, padding.top);
     size = constraints.constrain(new Size(
       padding.left + child.size.width + padding.right,
       padding.top + child.size.height + padding.bottom
@@ -238,7 +238,7 @@ class RenderPositionedBox extends RenderShiftedBox {
       size = constraints.constrain(new Size(shrinkWrapWidth ? child.size.width * (_widthFactor ?? 1.0) : double.INFINITY,
                                             shrinkWrapHeight ? child.size.height * (_heightFactor ?? 1.0) : double.INFINITY));
       final BoxParentData childParentData = child.parentData;
-      childParentData.position = _alignment.alongOffset(size - child.size).toPoint();
+      childParentData.offset = _alignment.alongOffset(size - child.size);
     } else {
       size = constraints.constrain(new Size(shrinkWrapWidth ? 0.0 : double.INFINITY,
                                             shrinkWrapHeight ? 0.0 : double.INFINITY));
@@ -260,7 +260,7 @@ class OneChildLayoutDelegate {
   BoxConstraints getConstraintsForChild(BoxConstraints constraints) => constraints;
 
   /// Returns the position where the child should be placed given the size of this object and the size of the child.
-  Point getPositionForChild(Size size, Size childSize) => Point.origin;
+  Offset getPositionForChild(Size size, Size childSize) => Offset.zero;
 
   /// Override this method to return true when the child needs to be laid out.
   bool shouldRelayout(OneChildLayoutDelegate oldDelegate) => true;
@@ -328,7 +328,7 @@ class RenderCustomOneChildLayoutBox extends RenderShiftedBox {
       assert(childConstraints.isNormalized);
       child.layout(childConstraints, parentUsesSize: !childConstraints.isTight);
       final BoxParentData childParentData = child.parentData;
-      childParentData.position = delegate.getPositionForChild(size, childConstraints.isTight ? childConstraints.smallest : child.size);
+      childParentData.offset = delegate.getPositionForChild(size, childConstraints.isTight ? childConstraints.smallest : child.size);
     }
   }
 }
@@ -376,7 +376,7 @@ class RenderBaseline extends RenderShiftedBox {
       size = constraints.constrain(child.size);
       double delta = baseline - child.getDistanceToBaseline(baselineType);
       final BoxParentData childParentData = child.parentData;
-      childParentData.position = new Point(0.0, delta);
+      childParentData.offset = new Offset(0.0, delta);
     } else {
       performResize();
     }

packages/flutter/lib/src/rendering/stack.dart

@@ -303,7 +303,7 @@ abstract class RenderStackBase extends RenderBox
         hasNonPositionedChildren = true;
 
         child.layout(constraints, parentUsesSize: true);
-        childParentData.position = Point.origin;
+        childParentData.offset = Offset.zero;
 
         final Size childSize = child.size;
         width = math.max(width, childSize.width);
@@ -328,7 +328,7 @@ abstract class RenderStackBase extends RenderBox
       final StackParentData childParentData = child.parentData;
 
       if (!childParentData.isPositioned) {
-        childParentData.position = alignment.alongOffset(size - child.size).toPoint();
+        childParentData.offset = alignment.alongOffset(size - child.size);
       } else {
         BoxConstraints childConstraints = const BoxConstraints();
 
@@ -362,7 +362,7 @@ abstract class RenderStackBase extends RenderBox
         if (y < 0.0 || y + child.size.height > size.height)
           _hasVisualOverflow = true;
 
-        childParentData.position = new Point(x, y);
+        childParentData.offset = new Offset(x, y);
       }
 
       assert(child.parentData == childParentData);
@@ -475,8 +475,8 @@ class RenderIndexedStack extends RenderStackBase {
     assert(position != null);
     RenderBox child = _childAtIndex();
     final StackParentData childParentData = child.parentData;
-    Point transformed = new Point(position.x - childParentData.position.x,
-                                  position.y - childParentData.position.y);
+    Point transformed = new Point(position.x - childParentData.offset.dx,
+                                  position.y - childParentData.offset.dy);
     return child.hitTest(result, position: transformed);
   }
 

packages/flutter/lib/src/rendering/viewport.dart

@@ -135,7 +135,7 @@ class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox
       child.layout(_getInnerConstraints(constraints), parentUsesSize: true);
       size = constraints.constrain(child.size);
       final BoxParentData childParentData = child.parentData;
-      childParentData.position = Point.origin;
+      childParentData.offset = Offset.zero;
     } else {
       performResize();
     }

packages/flutter/test/rendering/box_test.dart

@@ -87,7 +87,7 @@ void main() {
     layout(paddedBox);
 
     BoxParentData parentData = coloredBox.parentData;
-    expect(parentData.position.x, isNot(equals(0.0)));
+    expect(parentData.offset.dx, isNot(equals(0.0)));
 
     paddedBox.child = null;
     RenderConstrainedBox constraintedBox = new RenderConstrainedBox(
@@ -96,6 +96,6 @@ void main() {
     layout(constraintedBox);
 
     parentData = coloredBox.parentData;
-    expect(parentData.position.x, equals(0.0));
+    expect(parentData.offset.dx, equals(0.0));
   });
 }

packages/flutter/test/widget/custom_one_child_layout_test.dart

@@ -27,10 +27,10 @@ class TestOneChildLayoutDelegate extends OneChildLayoutDelegate {
     );
   }
 
-  Point getPositionForChild(Size size, Size childSize) {
+  Offset getPositionForChild(Size size, Size childSize) {
     sizeFromGetPositionForChild = size;
     childSizeFromGetPositionForChild = childSize;
-    return Point.origin;
+    return Offset.zero;
   }
 
   bool shouldRelayoutCalled = false;

packages/flutter/test/widget/positioned_test.dart

@@ -28,14 +28,14 @@ void main() {
         duration: const Duration(seconds: 10)
       );
       final List<Size> sizes = <Size>[];
-      final List<Point> positions = <Point>[];
+      final List<Offset> positions = <Offset>[];
       final GlobalKey key = new GlobalKey();
 
       void recordMetrics() {
         RenderBox box = key.currentContext.findRenderObject();
         BoxParentData boxParentData = box.parentData;
         sizes.add(box.size);
-        positions.add(boxParentData.position);
+        positions.add(boxParentData.offset);
       }
 
       tester.pumpWidget(
@@ -69,7 +69,7 @@ void main() {
       recordMetrics();
 
       expect(sizes, equals([const Size(10.0, 10.0), const Size(10.0, 10.0), const Size(10.0, 10.0), const Size(10.0, 10.0), const Size(10.0, 10.0), const Size(10.0, 10.0)]));
-      expect(positions, equals([const Point(10.0, 10.0), const Point(10.0, 10.0), const Point(17.0, 17.0), const Point(24.0, 24.0), const Point(45.0, 45.0), const Point(80.0, 80.0)]));
+      expect(positions, equals([const Offset(10.0, 10.0), const Offset(10.0, 10.0), const Offset(17.0, 17.0), const Offset(24.0, 24.0), const Offset(45.0, 45.0), const Offset(80.0, 80.0)]));
 
     });
   });

packages/flutter/test/widget/stack_test.dart

@@ -123,11 +123,11 @@ void main() {
 
       Element child0 = tester.findElementByKey(child0Key);
       final StackParentData child0RenderObjectParentData = child0.renderObject.parentData;
-      expect(child0RenderObjectParentData.position, equals(const Point(0.0, 0.0)));
+      expect(child0RenderObjectParentData.offset, equals(const Offset(0.0, 0.0)));
 
       Element child1 = tester.findElementByKey(child1Key);
       final StackParentData child1RenderObjectParentData = child1.renderObject.parentData;
-      expect(child1RenderObjectParentData.position, equals(const Point(5.0, 5.0)));
+      expect(child1RenderObjectParentData.offset, equals(const Offset(5.0, 5.0)));
     });
   });
 
@@ -233,8 +233,8 @@ void main() {
       expect(parentData.left, equals(10.0));
       expect(parentData.width, equals(11.0));
       expect(parentData.height, equals(12.0));
-      expect(parentData.position.x, equals(10.0));
-      expect(parentData.position.y, equals(0.0));
+      expect(parentData.offset.dx, equals(10.0));
+      expect(parentData.offset.dy, equals(0.0));
       expect(renderBox.size.width, equals(11.0));
       expect(renderBox.size.height, equals(12.0));
 
@@ -258,8 +258,8 @@ void main() {
       expect(parentData.left, isNull);
       expect(parentData.width, equals(11.0));
       expect(parentData.height, equals(12.0));
-      expect(parentData.position.x, equals(779.0));
-      expect(parentData.position.y, equals(0.0));
+      expect(parentData.offset.dx, equals(779.0));
+      expect(parentData.offset.dy, equals(0.0));
       expect(renderBox.size.width, equals(11.0));
       expect(renderBox.size.height, equals(12.0));
     });