From 6a62b7bbd93ddec21e0990d1bcdb16edf32d6b7a Mon Sep 17 00:00:00 2001
From: fufesou <linlong1266@gmail.com>
Date: Mon, 14 Sep 2026 11:18:03 +0800
Subject: [PATCH] Fix cursor alignment when a scrollbar axis stops overflowing

---
 flutter/lib/desktop/pages/remote_page.dart | 18 +++++++++++-------
 flutter/test/cursor_scroll_edge_test.dart  | 15 ++++++++++++---
 2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/flutter/lib/desktop/pages/remote_page.dart b/flutter/lib/desktop/pages/remote_page.dart
index 40f0fbe2d..ef6794f86 100644
--- a/flutter/lib/desktop/pages/remote_page.dart
+++ b/flutter/lib/desktop/pages/remote_page.dart
@@ -1220,9 +1220,10 @@ class _ImagePaintState extends State<ImagePaint> {
   // Layout can change scroll metrics without notification. Compare against this
   // build's fractions: a delayed refresh may already have changed the model.
   void _syncScrollAfterLayout(CanvasModel canvas) {
-    // Custom scrollbars also paint from scroll fractions; preserve Original's path.
+    // Both supported scrollbar view styles also paint from scroll fractions.
     if (canvas.scrollStyle != ScrollStyle.scrolledge &&
-        canvas.viewStyle.style != kRemoteViewStyleCustom) return;
+        canvas.viewStyle.style != kRemoteViewStyleCustom &&
+        canvas.viewStyle.style != kRemoteViewStyleOriginal) return;
     final renderedScroll = (canvas.scrollX, canvas.scrollY);
     SchedulerBinding.instance.addPostFrameCallback((_) {
       if (!mounted) return;
@@ -1434,11 +1435,14 @@ class CursorPaint extends StatelessWidget {
       // Scrollbar and edge scrolling share a layout that ignores canvas pan offsets.
       final imageWidth = rect.width * c.scale;
       final imageHeight = rect.height * c.scale;
-      // Match the integer centering in _buildCrossScrollbarFromLayout.
-      cx = (c.size.width > imageWidth ? (c.size.width - imageWidth) ~/ 2 : 0) -
-          imageWidth * c.scrollX;
-      cy = (c.size.height > imageHeight ? (c.size.height - imageHeight) ~/ 2 : 0) -
-          imageHeight * c.scrollY;
+      // Match the video's integer centering on each fitting axis, even if a
+      // detached scroll controller left a stale fraction before layout sync.
+      cx = c.size.width < imageWidth
+          ? -imageWidth * c.scrollX
+          : ((c.size.width - imageWidth) ~/ 2).toDouble();
+      cy = c.size.height < imageHeight
+          ? -imageHeight * c.scrollY
+          : ((c.size.height - imageHeight) ~/ 2).toDouble();
     }
 
     final image = m.image ?? preDefaultCursor.image;
diff --git a/flutter/test/cursor_scroll_edge_test.dart b/flutter/test/cursor_scroll_edge_test.dart
index cf1921935..f3f62afd7 100644
--- a/flutter/test/cursor_scroll_edge_test.dart
+++ b/flutter/test/cursor_scroll_edge_test.dart
@@ -16,6 +16,12 @@ import 'cursor_test_utils.dart';
 const _viewport = Size(200, 160);
 const _hotspot = Offset(4, 9);
 const _scrollDeltas = [80.0, -20.0, 1000.0, 1000.0, -1000.0, -1000.0, 80.0, 0.0];
+const _fittingViewports = [
+  Size(500, 160), // Fit horizontally while vertical scrolling remains.
+  Size(200, 400), // Fit vertically while horizontal scrolling remains.
+  Size(400, 160), // Exact fit also detaches the controller.
+  Size(200, 320),
+];
 
 class _Peer extends Fake implements FfiModel {
   _Peer(ui.Image frame)
@@ -118,6 +124,7 @@ class _FFI extends Fake implements FFI {
 
 void main() {
   for (final style in [(kRemoteViewStyleOriginal, ScrollStyle.scrolledge),
+    (kRemoteViewStyleOriginal, ScrollStyle.scrollbar),
     (kRemoteViewStyleCustom, ScrollStyle.scrolledge),
     (kRemoteViewStyleCustom, ScrollStyle.scrollbar)]) {
     for (final texture in [false, true]) {
@@ -203,17 +210,19 @@ Future<void> _checkRelayout(
     cursor.dispose();
   });
   await _mount(tester, ffi, 1);
-  canvas.performEdgeScroll(Vector2(20, 20));
-  await tester.pump();
   final videoWidget = texture ? find.byType(Texture) : _paintOf(video);
-  _expectAlignment(tester, ffi, videoWidget);
   for (final (viewport, dpr) in [
+    for (final viewport in _fittingViewports)
+      ...[(viewport, 1.0), (_viewport, 1.0)],
     (const Size(160, 120), 2.0),
     (const Size(195, 155), 2.0), // Clamp both existing scroll positions.
     (const Size(240, 155), 2.0), // Detach the horizontal scroll controller.
     (const Size(240, 200), 2.0), // No scrolling remains.
     (_viewport, 1.0),
   ]) {
+    canvas.performEdgeScroll(Vector2(20, 20));
+    await tester.pump();
+    _expectAlignment(tester, ffi, videoWidget);
     tester.view.devicePixelRatio = dpr;
     tester.view.physicalSize = viewport * dpr;
     canvas.relayout(viewport, dpr);