InteractiveViewer scroll direction (#60523)

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

@@ -848,7 +848,7 @@ class _InteractiveViewerState extends State<InteractiveViewer> with TickerProvid
     if (event is PointerScrollEvent) {
       final RenderBox childRenderBox = _childKey.currentContext.findRenderObject() as RenderBox;
       final Size childSize = childRenderBox.size;
-      final double scaleChange = 1.0 + event.scrollDelta.dy / childSize.height;
+      final double scaleChange = 1.0 - event.scrollDelta.dy / childSize.height;
       if (scaleChange == 0.0) {
         return;
       }

packages/flutter/test/widgets/gesture_utils.dart

@@ -7,10 +7,10 @@
 import 'package:flutter/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-Future<void> scrollAt(Offset position, WidgetTester tester) {
+Future<void> scrollAt(Offset position, WidgetTester tester, [Offset offset = const Offset(0.0, 20.0)]) {
   final TestPointer testPointer = TestPointer(1, PointerDeviceKind.mouse);
   // Create a hover event so that |testPointer| has a location when generating the scroll.
   testPointer.hover(position);
   final HitTestResult result = tester.hitTestOnBinding(position);
-  return tester.sendEventToBinding(testPointer.scroll(const Offset(0.0, 20.0)), result);
+  return tester.sendEventToBinding(testPointer.scroll(offset), result);
 }

packages/flutter/test/widgets/interactive_viewer_test.dart

@@ -422,7 +422,7 @@ void main() {
       );
 
       final Offset center = tester.getCenter(find.byType(InteractiveViewer));
-      await scrollAt(center, tester);
+      await scrollAt(center, tester, const Offset(0.0, -20.0));
       await tester.pumpAndSettle();
 
       expect(transformationController.value.getMaxScaleOnAxis(), greaterThan(1.0));
@@ -445,7 +445,7 @@ void main() {
       );
 
       final Offset center = tester.getCenter(find.byType(InteractiveViewer));
-      await scrollAt(center, tester);
+      await scrollAt(center, tester, const Offset(0.0, -20.0));
       await tester.pumpAndSettle();
 
       expect(transformationController.value.getMaxScaleOnAxis(), equals(1.0));