initial implementation of chrome api on osx.

native/Avalonia.Native/inc/avalonia-native.h

@@ -276,6 +276,7 @@ AVNCOM(IAvnWindow, 04) : virtual IAvnWindowBase
     virtual HRESULT SetTitleBarColor (AvnColor color) = 0;
     virtual HRESULT SetWindowState(AvnWindowState state) = 0;
     virtual HRESULT GetWindowState(AvnWindowState*ret) = 0;
+    virtual HRESULT SetExtendClientArea (bool enable) = 0;
 };
 
 AVNCOM(IAvnWindowBaseEvents, 05) : IUnknown

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

@@ -474,6 +474,7 @@ private:
     bool _inSetWindowState;
     NSRect _preZoomSize;
     bool _transitioningWindowState;
+    bool _isClientAreaExtended;
     
     FORWARD_IUNKNOWN()
     BEGIN_INTERFACE_MAP()
@@ -487,6 +488,7 @@ private:
     ComPtr<IAvnWindowEvents> WindowEvents;
     WindowImpl(IAvnWindowEvents* events, IAvnGlContext* gl) : WindowBaseImpl(events, gl)
     {
+        _isClientAreaExtended = false;
         _fullScreenActive = false;
         _canResize = true;
         _decorations = SystemDecorationsFull;
@@ -766,6 +768,28 @@ private:
         }
     }
     
+    virtual HRESULT SetExtendClientArea (bool enable) override
+    {
+        _isClientAreaExtended = enable;
+        [Window setTitleVisibility:NSWindowTitleHidden];
+        [Window setTitlebarAppearsTransparent:enable];
+        Window.movableByWindowBackground = true;
+        
+        NSRect x;
+        x.size.height = 50;
+        x.size.width = Window.frame.size.width;
+        [Window contentLayoutRect] = x;
+        
+        
+        auto customToolbar = [NSToolbar new];
+        
+        customToolbar.showsBaselineSeparator = true;
+        Window.toolbar = customToolbar;
+        
+        UpdateStyle();
+        return S_OK;
+    }
+    
     void EnterFullScreenMode ()
     {
         _fullScreenActive = true;
@@ -924,6 +948,11 @@ protected:
         {
             s |= NSWindowStyleMaskMiniaturizable;
         }
+        
+        if(_isClientAreaExtended)
+        {
+            s |= NSWindowStyleMaskFullSizeContentView | NSWindowStyleMaskTexturedBackground;
+        }
         return s;
     }
 };

src/Avalonia.Native/WindowImpl.cs

@@ -1,6 +1,8 @@
 using System;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
+using Avalonia.Input;
+using Avalonia.Input.Raw;
 using Avalonia.Native.Interop;
 using Avalonia.OpenGL;
 using Avalonia.Platform;
@@ -100,14 +102,43 @@ namespace Avalonia.Native
 
         public Action<bool> ExtendClientAreaToDecorationsChanged { get; set; }
 
-        public Thickness ExtendedMargins { get; } = new Thickness();
+        public Thickness ExtendedMargins { get; } = new Thickness(0, 20, 0, 0);
 
         public Thickness OffScreenMargin { get; } = new Thickness();
 
-        public bool IsClientAreaExtendedToDecorations { get; }
+        private bool _isExtended;
+        public bool IsClientAreaExtendedToDecorations => _isExtended;
+
+        protected override bool ChromeHitTest (RawPointerEventArgs e)
+        {
+            if(_isExtended)
+            {
+                if(e.Type == RawPointerEventType.LeftButtonDown)
+                {
+                    var visual = (_inputRoot as Window).Renderer.HitTestFirst(e.Position, _inputRoot as Window, x =>
+                            {
+                                if (x is IInputElement ie && !ie.IsHitTestVisible)
+                                {
+                                    return false;
+                                }
+                                return true;
+                            });
+
+                    if(visual == null)
+                    {
+                        _native.BeginMoveDrag();
+                    }
+                }
+            }
+
+            return false;
+        }
 
         public void SetExtendClientAreaToDecorationsHint(bool extendIntoClientAreaHint)
         {
+            _isExtended = extendIntoClientAreaHint;
+            _native.SetExtendClientArea(extendIntoClientAreaHint);
+            ExtendClientAreaToDecorationsChanged?.Invoke(true);
         }
 
         public void SetExtendClientAreaChromeHints(ExtendClientAreaChromeHints hints)

src/Avalonia.Native/WindowImplBase.cs

@@ -45,7 +45,7 @@ namespace Avalonia.Native
     public abstract class WindowBaseImpl : IWindowBaseImpl,
         IFramebufferPlatformSurface
     {
-        IInputRoot _inputRoot;
+        protected IInputRoot _inputRoot;
         IAvnWindowBase _native;
         private object _syncRoot = new object();
         private bool _deferredRendering = false;
@@ -254,6 +254,11 @@ namespace Avalonia.Native
             return args.Handled;
         }
 
+        protected virtual bool ChromeHitTest (RawPointerEventArgs e)
+        {
+            return false;
+        }
+
         public void RawMouseEvent(AvnRawMouseEventType type, uint timeStamp, AvnInputModifiers modifiers, AvnPoint point, AvnVector delta)
         {
             Dispatcher.UIThread.RunJobs(DispatcherPriority.Input + 1);
@@ -265,7 +270,12 @@ namespace Avalonia.Native
                     break;
 
                 default:
-                    Input?.Invoke(new RawPointerEventArgs(_mouse, timeStamp, _inputRoot, (RawPointerEventType)type, point.ToAvaloniaPoint(), (RawInputModifiers)modifiers));
+                    var e = new RawPointerEventArgs(_mouse, timeStamp, _inputRoot, (RawPointerEventType)type, point.ToAvaloniaPoint(), (RawInputModifiers)modifiers);
+                    
+                    if(!ChromeHitTest(e))
+                    {
+                        Input?.Invoke(e);
+                    }
                     break;
             }
         }