Change RenderObject.getTransformTo to include ancestor. (#37652)

getTransformTo now includes ancestor in the transform it returns, except
for if ancestor is the root view, ensuring that the transform remains in
logical pixel space.

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

@@ -1002,7 +1002,7 @@ class RenderListWheelViewport
     final ListWheelParentData parentData = child.parentData;
     final double targetOffset = parentData.offset.dy; // the so-called "centerPosition"
 
-    final Matrix4 transform = target.getTransformTo(this);
+    final Matrix4 transform = target.getTransformTo(child);
     final Rect bounds = MatrixUtils.transformRect(transform, rect);
     final Rect targetRect = bounds.translate(0.0, (size.height - itemExtent) / 2);
 

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

@@ -2171,6 +2171,7 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
   /// logical pixels. To get physical pixels, use [applyPaintTransform] from the
   /// [RenderView] to further transform the coordinate.
   Matrix4 getTransformTo(RenderObject ancestor) {
+    final bool ancestorSpecified = ancestor != null;
     assert(attached);
     if (ancestor == null) {
       final AbstractNode rootNode = owner.rootNode;
@@ -2182,6 +2183,8 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
       assert(renderer != null); // Failed to find ancestor in parent chain.
       renderers.add(renderer);
     }
+    if (ancestorSpecified)
+      renderers.add(ancestor);
     final Matrix4 transform = Matrix4.identity();
     for (int index = renderers.length - 1; index > 0; index -= 1) {
       renderers[index].applyPaintTransform(renderers[index - 1], transform);

packages/flutter/lib/src/widgets/single_child_scroll_view.dart

@@ -576,7 +576,7 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
       return RevealedOffset(offset: offset.pixels, rect: rect);
 
     final RenderBox targetBox = target;
-    final Matrix4 transform = targetBox.getTransformTo(this);
+    final Matrix4 transform = targetBox.getTransformTo(child);
     final Rect bounds = MatrixUtils.transformRect(transform, rect);
     final Size contentSize = child.size;
 

packages/flutter/test/rendering/box_test.dart

@@ -995,6 +995,17 @@ void main() {
         );
       }
     });
+
+    test('localToGlobal with ancestor', () {
+      final RenderConstrainedBox innerConstrained = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 50, height: 50));
+      final RenderPositionedBox innerCenter = RenderPositionedBox(alignment: Alignment.center, child: innerConstrained);
+      final RenderConstrainedBox outerConstrained = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 100, height: 100), child: innerCenter);
+      final RenderPositionedBox outerCentered = RenderPositionedBox(alignment: Alignment.center, child: outerConstrained);
+
+      layout(outerCentered);
+
+      expect(innerConstrained.localToGlobal(Offset.zero, ancestor: outerConstrained).dy, 25.0);
+    });
   });
 }