Nothing.h

#import <AppKit/AppKit.h>

// This window becomes main and key when the app loses focus, which ensures
// the "didBecomeKey" and "didBecomeMain" events are posted when they should be.
@interface Nothing : NSWindow <NSWindowDelegate>

- (instancetype)init;
- (instancetype)initWithContentRect:(NSRect)contentRect styleMask:(NSWindowStyleMask)style backing:(NSBackingStoreType)backingStoreType defer:(BOOL)flag NS_DESIGNATED_INITIALIZER;

@end

Nothing.m

#import "Nothing.h"
#import "DYApplication.h"

@implementation Nothing

- (instancetype)init
{
  return [self initWithContentRect:NSZeroRect
                         styleMask:NSWindowStyleMaskBorderless
                           backing:NSBackingStoreBuffered
                             defer:YES];
}

- (instancetype)initWithContentRect:(NSRect)contentRect styleMask:(NSWindowStyleMask)style backing:(NSBackingStoreType)backingStoreType defer:(BOOL)flag
{
  if (self = [super initWithContentRect:contentRect
                              styleMask:style
                                backing:backingStoreType
                                  defer:flag]
  ) {
    self.canHide = NO;
    self.collectionBehavior = NSWindowCollectionBehaviorIgnoresCycle | NSWindowCollectionBehaviorStationary;
    self.ignoresMouseEvents = YES;
    self.releasedWhenClosed = NO;
    self.delegate = self;
  }
  return self;
}

- (BOOL)canBecomeMainWindow
{
  return YES;
}

- (BOOL)canBecomeKeyWindow
{
  return YES;
}

- (void)windowDidBecomeKey:(NSNotification *)notification
{
  if (DYApp.isActive) {
    [DYApp blur];
  }
}

@end