osx: keep window creation on-screen during display reconfiguration (AvaloniaUI#21543)

* osx: anchor new windows to the primary screen origin

WindowBaseImpl::CreateNSWindow anchors the new NSWindow's content rect to the
primary screen's frame.origin. The primary screen is at Cocoa (0,0) on a
healthy Mac, but can be offset (often negative) while the display server is
mid-reconfiguration -- e.g. CGMainDisplayID() briefly returns 0 after
wake-from-sleep -- or on multi-monitor layouts where the primary is not at the
origin. Anchoring keeps the window on a real screen so it is positioned
on-screen and its flipped Position lands inside a Screen.Bounds.

See AvaloniaUI#18895.

Co-authored-by: Cursor <cursoragent@cursor.com>

* osx: keep window construction resilient when no screen contains it

When locating the screen that sizes a new window, fall back to a default size
if AppKit reports no screens -- or none whose bounds contain the last-known
position -- during a display reconfiguration. The window is repositioned on the
next ScreenChanged event once the display server settles.

See AvaloniaUI#18895.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Less verbose comments

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Julien Lebosquain <julien@lebosquain.net>

Author: 3 people

native/Avalonia.Native/src/OSX/WindowBaseImpl.mm

@@ -450,11 +450,21 @@ static void ActivateApplication() {
 }
 
 void WindowBaseImpl::CreateNSWindow(bool usePanel) {
+    // Anchor the content rect to the primary screen's origin. It's usually at (0,0), but can be offset while the
+    // display server is mid-reconfiguration. This ensures the window is always on a proper screen.
+    // See https://github.com/AvaloniaUI/Avalonia/issues/18895
+    NSPoint origin = NSZeroPoint;
+    NSArray<NSScreen*>* screens = [NSScreen screens];
+    if (screens.count > 0)
+        origin = screens.firstObject.frame.origin;
+
+    NSRect contentRect = NSRect { origin.x, origin.y, lastSize };
+
     if (usePanel) {
-        Window = [[AvnPanel alloc] initWithParent:this contentRect:NSRect{0, 0, lastSize} styleMask:NSWindowStyleMaskBorderless];
+        Window = [[AvnPanel alloc] initWithParent:this contentRect:contentRect styleMask:NSWindowStyleMaskBorderless];
         [Window setHidesOnDeactivate:false];
     } else {
-        Window = [[AvnWindow alloc] initWithParent:this contentRect:NSRect{0, 0, lastSize} styleMask:NSWindowStyleMaskBorderless];
+        Window = [[AvnWindow alloc] initWithParent:this contentRect:contentRect styleMask:NSWindowStyleMaskBorderless];
     }
 }
 

src/Avalonia.Native/WindowImplBase.cs

@@ -51,11 +51,23 @@ internal override void Init(MacOSTopLevelHandle handle)
 
             base.Init(handle);
 
+            int defaultWidth = 0, defaultHeight = 0;
+
             var monitor = this.TryGetFeature<IScreenImpl>()!.AllScreens
                 .OrderBy(x => x.Scaling)
-                .First(m => m.Bounds.Contains(Position));
+                .FirstOrDefault(m => m.Bounds.Contains(Position));
+
+            if (monitor != null)
+            {
+                // Emulate Windows 7+ default window size behavior.
+                defaultWidth = (int)(monitor.WorkingArea.Width * 0.75d);
+                defaultHeight = (int)(monitor.WorkingArea.Height * 0.7d);
+            }
+
+            defaultWidth = Math.Max(defaultWidth, 300);
+            defaultHeight = Math.Max(defaultHeight, 200);
 
-            Resize(new Size(monitor.WorkingArea.Width * 0.75d, monitor.WorkingArea.Height * 0.7d), WindowResizeReason.Layout);
+            Resize(new Size(defaultWidth, defaultHeight), WindowResizeReason.Layout);
         }
 
         public void Activate()