Improve menu popup positioning on macOS

Refactored the Menu::Open method to better handle window and view selection, coordinate conversion, and menu popup on the main run loop. This ensures more reliable context menu display, especially when the main or key window is available, and properly accounts for flipped views.

Author: lijy91

src/platform/macos/menu_macos.mm

@@ -790,28 +790,59 @@ - (void)menuDidClose:(NSMenu*)menu {
 }
 
 bool Menu::Open(double x, double y) {
-  NSPoint point = NSMakePoint(x, y);
-
-  // Convert screen coordinates to window coordinates if needed
-  NSEvent* event = [NSEvent mouseEventWithType:NSEventTypeRightMouseDown
-                                      location:point
-                                 modifierFlags:0
-                                     timestamp:0
-                                  windowNumber:0
-                                       context:nil
-                                   eventNumber:0
-                                    clickCount:1
-                                      pressure:1.0];
+  // Get the main window
+  NSWindow* mainWindow = [[NSApplication sharedApplication] mainWindow];
+  if (!mainWindow) {
+    // Fallback to key window if main window is not available
+    mainWindow = [[NSApplication sharedApplication] keyWindow];
+  }
+
+  if (!mainWindow) {
+    // If still no window, use the old implementation
+    NSPoint point = NSMakePoint(x, y);
+    NSEvent* event = [NSEvent mouseEventWithType:NSEventTypeRightMouseDown
+                                        location:point
+                                   modifierFlags:0
+                                       timestamp:0
+                                    windowNumber:0
+                                         context:nil
+                                     eventNumber:0
+                                      clickCount:1
+                                        pressure:1.0];
+
+    pimpl_->visible_ = true;
+
+    @autoreleasepool {
+      NSView* dummyView = [[NSView alloc] init];
+      [NSMenu popUpContextMenu:pimpl_->ns_menu_ withEvent:event forView:dummyView];
+    }
 
-  pimpl_->visible_ = true;
+    pimpl_->visible_ = false;
+    return true;
+  }
 
-  @autoreleasepool {
-    // Create a dummy view to avoid the nil warning
-    NSView* dummyView = [[NSView alloc] init];
-    [NSMenu popUpContextMenu:pimpl_->ns_menu_ withEvent:event forView:dummyView];
+  NSView* contentView = [mainWindow contentView];
+  if (!contentView) {
+    return false;
   }
 
-  pimpl_->visible_ = false;
+  // Convert coordinates if the content view is not flipped
+  // In macOS, the default coordinate system has origin at bottom-left
+  // If view is not flipped, we need to convert from top-left origin
+  CGFloat finalY = y;
+  if (![contentView isFlipped]) {
+    CGFloat frameHeight = [contentView frame].size.height;
+    finalY = frameHeight - y;
+  }
+
+  NSPoint point = NSMakePoint(x, finalY);
+
+  pimpl_->visible_ = true;
+
+  // Use dispatch to ensure menu popup happens on the main run loop
+  dispatch_async(dispatch_get_main_queue(), ^{
+    [pimpl_->ns_menu_ popUpMenuPositioningItem:nil atLocation:point inView:contentView];
+  });
 
   return true;
 }