Fix TabBar with padding is not centered (#113091)

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

@@ -1062,14 +1062,18 @@ class _TabBarState extends State<TabBar> {
       return 0.0;
     }
     double tabCenter = _indicatorPainter!.centerOf(index);
+    double paddingStart;
     switch (Directionality.of(context)) {
       case TextDirection.rtl:
+        paddingStart = widget.padding?.resolve(TextDirection.rtl).right ?? 0;
         tabCenter = _tabStripWidth - tabCenter;
         break;
       case TextDirection.ltr:
+        paddingStart = widget.padding?.resolve(TextDirection.ltr).left ?? 0;
         break;
     }
-    return clampDouble(tabCenter - viewportWidth / 2.0, minExtent, maxExtent);
+
+    return clampDouble(tabCenter + paddingStart - viewportWidth / 2.0, minExtent, maxExtent);
   }
 
   double _tabCenteredScrollOffset(int index) {

packages/flutter/test/material/tabs_test.dart

@@ -110,8 +110,11 @@ Widget buildFrame({
   bool isScrollable = false,
   Color? indicatorColor,
   Duration? animationDuration,
+  EdgeInsetsGeometry? padding,
+  TextDirection textDirection = TextDirection.ltr,
 }) {
   return boilerplate(
+    textDirection: textDirection,
     child: DefaultTabController(
       animationDuration: animationDuration,
       initialIndex: tabs.indexOf(value),
@@ -121,6 +124,7 @@ Widget buildFrame({
         tabs: tabs.map<Widget>((String tab) => Tab(text: tab)).toList(),
         isScrollable: isScrollable,
         indicatorColor: indicatorColor,
+        padding: padding,
       ),
     ),
   );
@@ -432,6 +436,54 @@ void main() {
     expect(tester.getCenter(find.text('FFFFFF')).dx, moreOrLessEquals(400.0, epsilon: 1.0));
   });
 
+  testWidgets('Scrollable TabBar, with padding, tap centers selected tab', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/112776
+    final List<String> tabs = <String>['AAAAAA', 'BBBBBB', 'CCCCCC', 'DDDDDD', 'EEEEEE', 'FFFFFF', 'GGGGGG', 'HHHHHH', 'IIIIII', 'JJJJJJ', 'KKKKKK', 'LLLLLL'];
+    const Key tabBarKey = Key('TabBar');
+    const EdgeInsetsGeometry padding = EdgeInsets.only(right: 30, left: 60);
+    await tester.pumpWidget(buildFrame(tabs: tabs, value: 'AAAAAA', isScrollable: true, tabBarKey: tabBarKey, padding: padding));
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    expect(controller, isNotNull);
+    expect(controller.index, 0);
+
+    expect(tester.getSize(find.byKey(tabBarKey)).width, equals(800.0));
+    // The center of the FFFFFF item is to the right of the TabBar's center
+    expect(tester.getCenter(find.text('FFFFFF')).dx, greaterThan(401.0));
+
+    await tester.tap(find.text('FFFFFF'));
+    await tester.pumpAndSettle();
+    expect(controller.index, 5);
+    // The center of the FFFFFF item is now at the TabBar's center
+    expect(tester.getCenter(find.text('FFFFFF')).dx, moreOrLessEquals(400.0, epsilon: 1.0));
+  });
+
+  testWidgets('Scrollable TabBar, with padding and TextDirection.rtl, tap centers selected tab', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/112776
+    final List<String> tabs = <String>['AAAAAA', 'BBBBBB', 'CCCCCC', 'DDDDDD', 'EEEEEE', 'FFFFFF', 'GGGGGG', 'HHHHHH', 'IIIIII', 'JJJJJJ', 'KKKKKK', 'LLLLLL'];
+    const Key tabBarKey = Key('TabBar');
+    const EdgeInsetsGeometry padding = EdgeInsets.only(right: 30, left: 60);
+    await tester.pumpWidget(buildFrame(
+      tabs: tabs,
+      value: 'AAAAAA',
+      isScrollable: true,
+      tabBarKey: tabBarKey,
+      padding: padding,
+      textDirection: TextDirection.rtl,
+    ));
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    expect(controller, isNotNull);
+    expect(controller.index, 0);
+
+    expect(tester.getSize(find.byKey(tabBarKey)).width, equals(800.0));
+    // The center of the FFFFFF item is to the left of the TabBar's center
+    expect(tester.getCenter(find.text('FFFFFF')).dx, lessThan(401.0));
+
+    await tester.tap(find.text('FFFFFF'));
+    await tester.pumpAndSettle();
+    expect(controller.index, 5);
+    // The center of the FFFFFF item is now at the TabBar's center
+    expect(tester.getCenter(find.text('FFFFFF')).dx, moreOrLessEquals(400.0, epsilon: 1.0));
+  });
 
   testWidgets('TabBar can be scrolled independent of the selection', (WidgetTester tester) async {
     final List<String> tabs = <String>['AAAA', 'BBBB', 'CCCC', 'DDDD', 'EEEE', 'FFFF', 'GGGG', 'HHHH', 'IIII', 'JJJJ', 'KKKK', 'LLLL'];