Fix tooltip position. (#60479)

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

@@ -284,8 +284,16 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
   }
 
   void _createNewEntry() {
+    final OverlayState overlayState = Overlay.of(
+      context,
+      debugRequiredFor: widget,
+    );
+
     final RenderBox box = context.findRenderObject() as RenderBox;
-    final Offset target = box.localToGlobal(box.size.center(Offset.zero));
+    final Offset target = box.localToGlobal(
+      box.size.center(Offset.zero),
+      ancestor: overlayState.context.findRenderObject(),
+    );
 
     // We create this widget outside of the overlay entry's builder to prevent
     // updated values from happening to leak into the overlay when the overlay
@@ -309,7 +317,7 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
       ),
     );
     _entry = OverlayEntry(builder: (BuildContext context) => overlay);
-    Overlay.of(context, debugRequiredFor: widget).insert(_entry);
+    overlayState.insert(_entry);
     SemanticsService.tooltip(widget.message);
   }
 

packages/flutter/test/material/tooltip_test.dart

@@ -99,6 +99,68 @@ void main() {
     expect(tipInGlobal.dy, 20.0);
   });
 
+  testWidgets('Does tooltip end up in the right place - center with padding outside overlay', (WidgetTester tester) async {
+    final GlobalKey key = GlobalKey();
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Padding(
+          padding: const EdgeInsets.all(20),
+          child: Overlay(
+            initialEntries: <OverlayEntry>[
+              OverlayEntry(
+                builder: (BuildContext context) {
+                  return Stack(
+                    children: <Widget>[
+                      Positioned(
+                        left: 300.0,
+                        top: 0.0,
+                        child: Tooltip(
+                          key: key,
+                          message: tooltipText,
+                          height: 20.0,
+                          padding: const EdgeInsets.all(5.0),
+                          verticalOffset: 20.0,
+                          preferBelow: false,
+                          child: const SizedBox(
+                            width: 0.0,
+                            height: 0.0,
+                          ),
+                        ),
+                      ),
+                    ],
+                  );
+                },
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+    (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
+    await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
+
+    /************************ 800x600 screen
+     *   ________________   * }- 20.0 padding outside overlay
+     *  |    o           |  * y=0
+     *  |    |           |  * }- 20.0 vertical offset, of which 10.0 is in the screen edge margin
+     *  | +----+         |  * \- (5.0 padding in height)
+     *  | |    |         |  * |- 20 height
+     *  | +----+         |  * /- (5.0 padding in height)
+     *  |________________|  *
+     *                      * } - 20.0 padding outside overlay
+     ************************/
+
+    final RenderBox tip = tester.renderObject(
+      _findTooltipContainer(tooltipText),
+    );
+    final Offset tipInGlobal = tip.localToGlobal(tip.size.topCenter(Offset.zero));
+    // The exact position of the left side depends on the font the test framework
+    // happens to pick, so we don't test that.
+    expect(tipInGlobal.dx, 320.0);
+    expect(tipInGlobal.dy, 40.0);
+  });
+
   testWidgets('Does tooltip end up in the right place - top left', (WidgetTester tester) async {
     final GlobalKey key = GlobalKey();
     await tester.pumpWidget(