fix(flutter): read the live DPR and clamp the painted cursor like the native one

CanvasModel caches devicePixelRatio and only refreshes it when the view
style changes, so after the window moves to a monitor with a different
DPR the unzoomed cursor kept the previous monitor's scale. Read it from
MediaQuery instead, which also rebuilds the cursor when it changes.

The native path clamps the scaled bitmap to kMinCursorSize; apply the
same clamp to the painted cursor so a small cursor does not change size
when the peer moves the mouse.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8HSHTEHo27mDcJXVyVfSP

flutter/lib/desktop/pages/remote_page.dart

@@ -1101,6 +1101,9 @@ class _ImagePaintState extends State<ImagePaint> {
     final m = Provider.of<ImageModel>(context);
     var c = Provider.of<CanvasModel>(context);
     final s = c.scale;
+    // CanvasModel caches the DPR and only refreshes it when the view style
+    // changes, so read it live to follow the window across monitors.
+    final dpr = MediaQuery.devicePixelRatioOf(context);
 
     bool isViewAdaptive() => c.viewStyle.style == kRemoteViewStyleAdaptive;
     bool isViewOriginal() => c.viewStyle.style == kRemoteViewStyleOriginal;
@@ -1117,6 +1120,12 @@ class _ImagePaintState extends State<ImagePaint> {
             } else {
               if (zoomCursor.value || isViewOriginal()) {
                 cursorScale = s;
+              } else {
+                // NSCursor and GdkCursor treat the bitmap size as logical
+                // pixels, so an unzoomed cursor must be shrunk by the DPR to
+                // keep 1 remote px == 1 physical px, the size Original view
+                // already renders it at.
+                cursorScale = 1.0 / dpr;
               }
             }
             return cursorScale;
@@ -1404,14 +1413,29 @@ class CursorPaint extends StatelessWidget {
       }
     }
 
-    double x = (m.x - hotx) * c.scale + cx;
-    double y = (m.y - hoty) * c.scale + cy;
+    double x = m.x * c.scale + cx - hotx;
+    double y = m.y * c.scale + cy - hoty;
     double scale = 1.0;
     final isViewOriginal = c.viewStyle.style == kRemoteViewStyleOriginal;
     if (zoomCursor.value || isViewOriginal) {
       x = m.x - hotx + cx / c.scale;
       y = m.y - hoty + cy / c.scale;
       scale = c.scale;
+    } else if (!isWindows) {
+      // Keep the painted cursor the same physical size as the native one
+      // built by getCursorScale() above, including its min-size clamp.
+      scale = 1.0 / MediaQuery.devicePixelRatioOf(context);
+      final image = m.image ?? preDefaultCursor.image;
+      if (scale != 1.0 &&
+          image != null &&
+          ((image.width * scale).toInt() < kMinCursorSize ||
+              (image.height * scale).toInt() < kMinCursorSize)) {
+        final sw = kMinCursorSize / image.width;
+        final sh = kMinCursorSize / image.height;
+        scale = sw < sh ? sh : sw;
+      }
+      x = (m.x * c.scale + cx) / scale - hotx;
+      y = (m.y * c.scale + cy) / scale - hoty;
     }
 
     return CustomPaint(

flutter/lib/models/model.dart

@@ -2884,7 +2884,7 @@ class CursorData {
     if (scale != 1.0) {
       // Update data if scale changed.
       final tgtWidth = (width * scale).toInt();
-      final tgtHeight = (width * scale).toInt();
+      final tgtHeight = (height * scale).toInt();
       if (tgtWidth < kMinCursorSize || tgtHeight < kMinCursorSize) {
         double sw = kMinCursorSize.toDouble() / width;
         double sh = kMinCursorSize.toDouble() / height;