[Input] Added KeyModifiers enumeration

KeyModifiers are represented as a bitwise combination of the Alt,
Control and Shift keys.

Source/OpenTK/Input/KeyModifiers.cs

@@ -0,0 +1,57 @@
+#region License
+//
+// HatPosition.cs
+//
+// Author:
+//       Stefanos A. <stapostol@gmail.com>
+//
+// Copyright (c) 2006-2014 Stefanos Apostolopoulos
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace OpenTK.Input
+{
+    /// <summary>
+    /// Enumerates modifier keys.
+    /// </summary>
+    [Flags]
+    public enum KeyModifiers : byte
+    {
+        /// <summary>
+        /// The alt key modifier (option on Mac).
+        /// </summary>
+        Alt = 1 << 0,
+
+        /// <summary>
+        /// The control key modifier.
+        /// </summary>
+        Control = 1 << 1,
+
+        /// <summary>
+        /// The shift key modifier.
+        /// </summary>
+        Shift = 1 << 2
+    }
+}

Source/OpenTK/OpenTK.csproj

@@ -801,6 +801,7 @@
     <Compile Include="Input\JoystickHat.cs" />
     <Compile Include="Input\HatPosition.cs" />
     <Compile Include="Input\JoystickHatState.cs" />
+    <Compile Include="Input\KeyModifiers.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <PropertyGroup>