Add modal window treatment to macOS

Before this addition, when a modal window was active,
it was allowed to bring other windows to the front (which
should be prohibited).
This addition is part of the solution for the issue
aseprite/aseprite#4561 'Inactive windows in multiple-window UI mode
pass events to below windows'

os/osx/window.mm

@@ -1,5 +1,5 @@
 // LAF OS Library
-// Copyright (C) 2019-2021  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 // Copyright (C) 2012-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -122,6 +122,9 @@ - (WindowOSXObjc*)initWithImpl:(os::WindowOSX*)impl
       self.hidesOnDeactivate = true;
     }
 
+    if (spec->modal())
+      self.level = NSModalPanelWindowLevel;
+
     // Hide the "View > Show Tab Bar" menu item
     if ([self respondsToSelector:@selector(setTabbingMode:)])
       [self setTabbingMode:NSWindowTabbingModeDisallowed];
@@ -366,6 +369,9 @@ - (void)noResponderFor:(SEL)eventSelector
 
 void WindowOSX::activate()
 {
+  if ([m_nsWindow.delegate respondsToSelector:@selector(windowShouldBecomeKey:)] &&
+      ![(id)m_nsWindow.delegate windowShouldBecomeKey:m_nsWindow])
+    return;
   [m_nsWindow makeKeyWindow];
 }
 

os/osx/window_delegate.h

@@ -1,5 +1,5 @@
 // LAF OS Library
-// Copyright (C) 2020-2021  Igara Studio S.A.
+// Copyright (C) 2020-2024  Igara Studio S.A.
 // Copyright (C) 2015  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -117,4 +117,10 @@ namespace os {
   return YES;
 }
 
+- (BOOL)windowShouldBecomeKey:(NSWindow *)sender
+{
+  NSWindow* modalWindow = [NSApp modalWindow];
+  return !modalWindow || modalWindow == sender;
+}
+
 @end

os/window_spec.h

@@ -1,5 +1,5 @@
 // LAF OS Library
-// Copyright (C) 2019-2021  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -43,6 +43,7 @@ namespace os {
     bool resizable() const { return m_resizable; }
     bool floating() const { return m_floating; }
     bool transparent() const { return m_transparent; }
+    bool modal() const { return m_modal; }
 
     // Parent window used for floating windows
     Window* parent() const { return m_parent; }
@@ -57,6 +58,7 @@ namespace os {
     void floating(const bool s) { m_floating = s; }
     void transparent(const bool s) { m_transparent = s; }
     void parent(Window* p) { m_parent = p; }
+    void modal(const bool s) { m_modal = s; }
 
     const gfx::Rect& frame() const { return m_frame; }
     const gfx::Rect& contentRect() const { return m_contentRect; }
@@ -78,6 +80,7 @@ namespace os {
     bool m_resizable = true;
     bool m_floating = false;
     bool m_transparent = false;
+    bool m_modal = false;
     gfx::Rect m_frame;
     gfx::Rect m_contentRect;
     int m_scale = 1;