Widget coordinate transforms: localToGlobal(), globalToLocal()

sky/packages/sky/lib/rendering/block.dart

@@ -6,6 +6,7 @@ import 'dart:math' as math;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:vector_math/vector_math.dart';
 
 class BlockParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> { }
 
@@ -248,6 +249,11 @@ class RenderBlockViewport extends RenderBlockBase {
     canvas.restore();
   }
 
+  void applyPaintTransform(Matrix4 transform) {
+    super.applyPaintTransform(transform);
+    transform.translate(0.0, startOffset);
+  }
+
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position + new Offset(0.0, -startOffset));
   }

sky/packages/sky/lib/rendering/box.dart

@@ -450,6 +450,42 @@ abstract class RenderBox extends RenderObject {
     _size = inDebugBuild ? new _DebugSize(value, this, debugCanParentUseSize) : value;
   }
 
+  void applyPaintTransform(Matrix4 transform) {
+    if (parentData is BoxParentData) {
+      Point position = (parentData as BoxParentData).position;
+      transform.translate(position.x, position.y);
+    }
+  }
+
+  static Point _transformPoint(Matrix4 transform, Point point) {
+    Vector3 position3 = new Vector3(point.x, point.y, 0.0);
+    Vector3 transformed3 = transform.transform3(position3);
+    return new Point(transformed3.x, transformed3.y);
+  }
+
+  Point globalToLocal(Point point) {
+    assert(attached);
+    Matrix4 transform = new Matrix4.identity();
+    RenderObject renderer = this;
+    while(renderer != null) {
+      renderer.applyPaintTransform(transform);
+      renderer = renderer.parent;
+    }
+    /* double det = */ transform.invert();
+    // TODO(abarth): Check the determinant for degeneracy.
+    return _transformPoint(transform, point);
+  }
+
+  Point localToGlobal(Point point) {
+    List <RenderObject> renderers = <RenderObject>[];
+    for (RenderObject renderer = this; renderer != null; renderer = renderer.parent)
+      renderers.add(renderer);
+    Matrix4 transform = new Matrix4.identity();
+    for (RenderObject renderer in renderers.reversed)
+      renderer.applyPaintTransform(transform);
+    return _transformPoint(transform, point);
+  }
+
   Rect get paintBounds => Point.origin & size;
   void debugPaint(PaintingCanvas canvas, Offset offset) {
     if (debugPaintSizeEnabled)
@@ -550,7 +586,6 @@ class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox
     if (child != null)
       canvas.paintChild(child, offset.toPoint());
   }
-
 }
 
 class RenderConstrainedBox extends RenderProxyBox {
@@ -1261,6 +1296,11 @@ class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox
     }
   }
 
+  void applyPaintTransform(Matrix4 transform) {
+    super.applyPaintTransform(transform);
+    transform.translate(-scrollOffset.dx, -scrollOffset.dy);
+  }
+
   void hitTestChildren(HitTestResult result, { Point position }) {
     if (child != null) {
       assert(child.parentData is BoxParentData);
@@ -1512,6 +1552,11 @@ class RenderTransform extends RenderProxyBox {
     canvas.restore();
   }
 
+  void applyPaintTransform(Matrix4 transform) {
+    super.applyPaintTransform(transform);
+    transform.multiply(_transform);
+  }
+
   String debugDescribeSettings(String prefix) {
     List<String> result = _transform.toString().split('\n').map((s) => '$prefix  $s\n').toList();
     result.removeLast();

sky/packages/sky/lib/rendering/object.dart

@@ -10,6 +10,7 @@ import 'package:sky/base/debug.dart';
 import 'package:sky/base/hit_test.dart';
 import 'package:sky/base/node.dart';
 import 'package:sky/base/scheduler.dart' as scheduler;
+import 'package:vector_math/vector_math.dart';
 
 export 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 export 'package:sky/base/hit_test.dart' show EventDisposition, HitTestTarget, HitTestEntry, HitTestResult;
@@ -412,6 +413,8 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   void debugPaint(PaintingCanvas canvas, Offset offset) { }
   void paint(PaintingCanvas canvas, Offset offset) { }
 
+  void applyPaintTransform(Matrix4 transform) { }
+
 
   // EVENTS
 

sky/packages/sky/lib/widgets/framework.dart

@@ -369,6 +369,21 @@ abstract class Widget {
     return '$runtimeType($key; hashCode=$hashCode)';
   }
 
+  // This function can be safely called when the layout is valid.
+  // For example Listener or SizeObserver callbacks can safely call
+  // globalToLocal().
+  Point globalToLocal(Point point) {
+    assert(mounted);
+    assert(root is RenderBox);
+    return (root as RenderBox).globalToLocal(point);
+  }
+
+  // See globalToLocal().
+  Point localToGlobal(Point point) {
+    assert(mounted);
+    assert(root is RenderBox);
+    return (root as RenderBox).localToGlobal(point);
+  }
 }