WindowImpl on Win32 when no system decorations will not cover taskbar.

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -15,6 +15,7 @@ using Avalonia.Input.Raw;
 using Avalonia.Platform;
 using Avalonia.Win32.Input;
 using Avalonia.Win32.Interop;
+using static Avalonia.Win32.Interop.UnmanagedMethods;
 
 namespace Avalonia.Win32
 {
@@ -135,7 +136,7 @@ namespace Avalonia.Win32
             {
                 var placement = default(UnmanagedMethods.WINDOWPLACEMENT);
                 UnmanagedMethods.GetWindowPlacement(_hwnd, ref placement);
-                
+
                 switch (placement.ShowCmd)
                 {
                     case UnmanagedMethods.ShowWindowCommand.Maximize:
@@ -184,22 +185,32 @@ namespace Avalonia.Win32
         public void SetSystemDecorations(bool value)
         {
             if (value == _decorated)
+            {
                 return;
-            var style = (UnmanagedMethods.WindowStyles) UnmanagedMethods.GetWindowLong(_hwnd, -16);
+            }
+
+            var style = (UnmanagedMethods.WindowStyles)UnmanagedMethods.GetWindowLong(_hwnd, -16);
+
             style |= UnmanagedMethods.WindowStyles.WS_OVERLAPPEDWINDOW;
+
             if (!value)
+            {
                 style ^= UnmanagedMethods.WindowStyles.WS_OVERLAPPEDWINDOW;
+            }
 
             UnmanagedMethods.RECT windowRect;
 
             UnmanagedMethods.GetWindowRect(_hwnd, out windowRect);
+
             Rect newRect;
             var oldThickness = BorderThickness;
 
-            UnmanagedMethods.SetWindowLong(_hwnd, -16, (uint) style);
+            UnmanagedMethods.SetWindowLong(_hwnd, -16, (uint)style);
+
             if (value)
             {
                 var thickness = BorderThickness;
+
                 newRect = new Rect(
                     windowRect.left - thickness.Left,
                     windowRect.top - thickness.Top,
@@ -207,19 +218,20 @@ namespace Avalonia.Win32
                     (windowRect.bottom - windowRect.top) + (thickness.Top + thickness.Bottom));
             }
             else
+            {
                 newRect = new Rect(
-                    windowRect.left + oldThickness.Left,
-                    windowRect.top + oldThickness.Top,
-                    (windowRect.right - windowRect.left) - (oldThickness.Left + oldThickness.Right),
-                    (windowRect.bottom - windowRect.top) - (oldThickness.Top + oldThickness.Bottom));
-            UnmanagedMethods.SetWindowPos(_hwnd, IntPtr.Zero, (int) newRect.X, (int) newRect.Y, (int) newRect.Width,
-                (int) newRect.Height,
+                windowRect.left + oldThickness.Left,
+                windowRect.top + oldThickness.Top,
+                (windowRect.right - windowRect.left) - (oldThickness.Left + oldThickness.Right),
+                (windowRect.bottom - windowRect.top) - (oldThickness.Top + oldThickness.Bottom));
+            }
+
+            UnmanagedMethods.SetWindowPos(_hwnd, IntPtr.Zero, (int)newRect.X, (int)newRect.Y, (int)newRect.Width,
+                (int)newRect.Height,
                 UnmanagedMethods.SetWindowPosFlags.SWP_NOZORDER | UnmanagedMethods.SetWindowPosFlags.SWP_NOACTIVATE);
 
 
             _decorated = value;
-
-
         }
 
         public void Invalidate(Rect rect)
@@ -268,7 +280,7 @@ namespace Avalonia.Win32
 
         public void BeginMoveDrag()
         {
-            UnmanagedMethods.DefWindowProc(_hwnd, (int) UnmanagedMethods.WindowsMessage.WM_NCLBUTTONDOWN,
+            UnmanagedMethods.DefWindowProc(_hwnd, (int)UnmanagedMethods.WindowsMessage.WM_NCLBUTTONDOWN,
                 new IntPtr((int)UnmanagedMethods.HitTestValues.HTCAPTION), IntPtr.Zero);
         }
 
@@ -286,8 +298,8 @@ namespace Avalonia.Win32
 
         public void BeginResizeDrag(WindowEdge edge)
         {
-            UnmanagedMethods.DefWindowProc(_hwnd, (int) UnmanagedMethods.WindowsMessage.WM_NCLBUTTONDOWN,
-                new IntPtr((int) EdgeDic[edge]), IntPtr.Zero);
+            UnmanagedMethods.DefWindowProc(_hwnd, (int)UnmanagedMethods.WindowsMessage.WM_NCLBUTTONDOWN,
+                new IntPtr((int)EdgeDic[edge]), IntPtr.Zero);
         }
 
         public Point Position
@@ -303,8 +315,8 @@ namespace Avalonia.Win32
                 UnmanagedMethods.SetWindowPos(
                     Handle.Handle,
                     IntPtr.Zero,
-                    (int) value.X,
-                    (int) value.Y,
+                    (int)value.X,
+                    (int)value.Y,
                     0,
                     0,
                     UnmanagedMethods.SetWindowPosFlags.SWP_NOSIZE | UnmanagedMethods.SetWindowPosFlags.SWP_NOACTIVATE);
@@ -454,7 +466,7 @@ namespace Avalonia.Win32
                                 : RawMouseEventType.MiddleButtonDown,
                         DipFromLParam(lParam), GetMouseModifiers(wParam));
                     break;
-                    
+
                 case UnmanagedMethods.WindowsMessage.WM_LBUTTONUP:
                 case UnmanagedMethods.WindowsMessage.WM_RBUTTONUP:
                 case UnmanagedMethods.WindowsMessage.WM_MBUTTONUP:
@@ -462,9 +474,9 @@ namespace Avalonia.Win32
                         WindowsMouseDevice.Instance,
                         timestamp,
                         _owner,
-                        msg == (int) UnmanagedMethods.WindowsMessage.WM_LBUTTONUP
+                        msg == (int)UnmanagedMethods.WindowsMessage.WM_LBUTTONUP
                             ? RawMouseEventType.LeftButtonUp
-                            : msg == (int) UnmanagedMethods.WindowsMessage.WM_RBUTTONUP
+                            : msg == (int)UnmanagedMethods.WindowsMessage.WM_RBUTTONUP
                                 ? RawMouseEventType.RightButtonUp
                                 : RawMouseEventType.MiddleButtonUp,
                         DipFromLParam(lParam), GetMouseModifiers(wParam));
@@ -508,7 +520,7 @@ namespace Avalonia.Win32
                         timestamp,
                         _owner,
                         ScreenToClient(DipFromLParam(lParam)),
-                        new Vector(-(ToInt32(wParam) >> 16) / wheelDelta,0), GetMouseModifiers(wParam));
+                        new Vector(-(ToInt32(wParam) >> 16) / wheelDelta, 0), GetMouseModifiers(wParam));
                     break;
 
                 case UnmanagedMethods.WindowsMessage.WM_MOUSELEAVE:
@@ -585,9 +597,9 @@ namespace Avalonia.Win32
             var modifiers = WindowsKeyboardDevice.Instance.Modifiers;
             if (keys.HasFlag(UnmanagedMethods.ModifierKeys.MK_LBUTTON))
                 modifiers |= InputModifiers.LeftMouseButton;
-            if(keys.HasFlag(UnmanagedMethods.ModifierKeys.MK_RBUTTON))
-                modifiers  |= InputModifiers.RightMouseButton;
-            if(keys.HasFlag(UnmanagedMethods.ModifierKeys.MK_MBUTTON))
+            if (keys.HasFlag(UnmanagedMethods.ModifierKeys.MK_RBUTTON))
+                modifiers |= InputModifiers.RightMouseButton;
+            if (keys.HasFlag(UnmanagedMethods.ModifierKeys.MK_MBUTTON))
                 modifiers |= InputModifiers.MiddleMouseButton;
             return modifiers;
         }
@@ -666,6 +678,8 @@ namespace Avalonia.Win32
         {
             UnmanagedMethods.ShowWindowCommand command;
 
+            bool doShow = true;
+
             switch (state)
             {
                 case WindowState.Minimized:
@@ -673,7 +687,31 @@ namespace Avalonia.Win32
                     break;
                 case WindowState.Maximized:
                     command = UnmanagedMethods.ShowWindowCommand.Maximize;
+
+                    if (!_decorated)
+                    {
+                        IntPtr monitor = MonitorFromWindow(_hwnd, MONITOR.MONITOR_DEFAULTTONEAREST);
+
+                        if (monitor != IntPtr.Zero)
+                        {
+                            MONITORINFO monitorInfo = new MONITORINFO();
+
+                            if (UnmanagedMethods.GetMonitorInfo(monitor, monitorInfo))
+                            {
+                                RECT rcMonitorArea = monitorInfo.rcMonitor;
+
+                                var x = monitorInfo.rcWork.left;
+                                var y = monitorInfo.rcWork.top;
+                                var cx = Math.Abs(monitorInfo.rcWork.right - x);
+                                var cy = Math.Abs(monitorInfo.rcWork.bottom - y);
+
+                                doShow = false;
+                                UnmanagedMethods.SetWindowPos(_hwnd, new IntPtr(-2), x, y, cx, cy, SetWindowPosFlags.SWP_SHOWWINDOW);
+                            }
+                        }
+                    }
                     break;
+
                 case WindowState.Normal:
                     command = UnmanagedMethods.ShowWindowCommand.Restore;
                     break;
@@ -681,7 +719,11 @@ namespace Avalonia.Win32
                     throw new ArgumentException("Invalid WindowState.");
             }
 
-            UnmanagedMethods.ShowWindow(_hwnd, command);
+            if (doShow)
+            {
+                UnmanagedMethods.ShowWindow(_hwnd, command);
+            }
+
             UnmanagedMethods.SetFocus(_hwnd);
         }