Add blank cursor

src/Avalonia.Input/Cursors.cs

@@ -38,6 +38,7 @@ namespace Avalonia.Input
         DragMove,
         DragCopy,
         DragLink,
+        None,
 
         // Not available in GTK directly, see http://www.pixelbeat.org/programming/x_cursors/ 
         // We might enable them later, preferably, by loading pixmax direclty from theme with fallback image

src/Avalonia.X11/X11CursorFactory.cs

@@ -8,6 +8,8 @@ namespace Avalonia.X11
 {
     class X11CursorFactory : IStandardCursorFactory
     {
+        private static IntPtr _nullCursor;
+        
         private readonly IntPtr _display;
         private Dictionary<CursorFontShape, IntPtr> _cursors;
 
@@ -42,16 +44,34 @@ namespace Avalonia.X11
         public X11CursorFactory(IntPtr display)
         {
             _display = display;
+            _nullCursor = GetNullCursor(display);
             _cursors = Enum.GetValues(typeof(CursorFontShape)).Cast<CursorFontShape>()
                 .ToDictionary(id => id, id => XLib.XCreateFontCursor(_display, id));
         }
         
         public IPlatformHandle GetCursor(StandardCursorType cursorType)
         {
-            var handle = s_mapping.TryGetValue(cursorType, out var shape)
+            IntPtr handle;
+            if (cursorType == StandardCursorType.None)
+            {
+                handle = _nullCursor;
+            }
+            else
+            {
+                handle = s_mapping.TryGetValue(cursorType, out var shape)
                 ? _cursors[shape]
                 : _cursors[CursorFontShape.XC_top_left_arrow];
+            }            
             return new PlatformHandle(handle, "XCURSOR");
         }
+
+        private static IntPtr GetNullCursor(IntPtr display)
+        {            
+            XColor color = new XColor();
+            byte[] data = new byte[] { 0 };
+            IntPtr window = XLib.XRootWindow(display, 0);
+            IntPtr pixmap = XLib.XCreatePixmapFromBitmapData(display, window, data, 1, 1, IntPtr.Zero, IntPtr.Zero, 0);
+            return XLib.XCreatePixmapCursor(display, pixmap, pixmap, ref color, ref color, 0, 0);            
+        }
     }
 }

src/Gtk/Avalonia.Gtk3/CursorFactory.cs

@@ -12,7 +12,8 @@ namespace Avalonia.Gtk3
         private static readonly Dictionary<StandardCursorType, object> CursorTypeMapping = new Dictionary
     <StandardCursorType, object>
         {
-            {StandardCursorType.AppStarting, CursorType.Watch},
+            {StandardCursorType.None, CursorType.Blank},
+            { StandardCursorType.AppStarting, CursorType.Watch},
             {StandardCursorType.Arrow, CursorType.LeftPtr},
             {StandardCursorType.Cross, CursorType.Cross},
             {StandardCursorType.Hand, CursorType.Hand1},
@@ -36,7 +37,7 @@ namespace Avalonia.Gtk3
             {StandardCursorType.BottomRightCorner, CursorType.BottomRightCorner},
             {StandardCursorType.DragCopy, CursorType.CenterPtr},
             {StandardCursorType.DragMove, CursorType.Fleur},
-            {StandardCursorType.DragLink, CursorType.Cross},
+            {StandardCursorType.DragLink, CursorType.Cross},            
         };
 
         private static readonly Dictionary<StandardCursorType, IPlatformHandle> Cache =
@@ -80,4 +81,4 @@ namespace Avalonia.Gtk3
             return rv;
         }
     }
-}
+}

src/Gtk/Avalonia.Gtk3/GdkCursor.cs

@@ -2,6 +2,7 @@
 {
     enum GdkCursorType
     {
+        Blank = -2,
         CursorIsPixmap = -1,
         XCursor = 0,
         Arrow = 2,

src/Windows/Avalonia.Win32/CursorFactory.cs

@@ -41,7 +41,8 @@ namespace Avalonia.Win32
         private static readonly Dictionary<StandardCursorType, int> CursorTypeMapping = new Dictionary
             <StandardCursorType, int>
         {
-            {StandardCursorType.AppStarting, 32650},
+            {StandardCursorType.None, 0},
+            { StandardCursorType.AppStarting, 32650},
             {StandardCursorType.Arrow, 32512},
             {StandardCursorType.Cross, 32515},
             {StandardCursorType.Hand, 32649},
@@ -69,7 +70,7 @@ namespace Avalonia.Win32
             // Fallback, should have been loaded from ole32.dll
             {StandardCursorType.DragMove, 32516},
             {StandardCursorType.DragCopy, 32516},
-            {StandardCursorType.DragLink, 32516},
+            {StandardCursorType.DragLink, 32516},            
         };
 
         private static readonly Dictionary<StandardCursorType, IPlatformHandle> Cache =