keyboard uses Button instead of ButtonState

src/Input/Keyboard.cs

@@ -7,7 +7,7 @@ namespace MoonWorks.Input
 {
 	public class Keyboard
 	{
-		private ButtonState[] Keys { get; }
+		private Button[] Keys { get; }
 		private int numKeys;
 
 		private static readonly char[] TextInputCharacters = new char[]
@@ -36,10 +36,10 @@ namespace MoonWorks.Input
 		{
 			SDL.SDL_GetKeyboardState(out numKeys);
 
-			Keys = new ButtonState[numKeys];
+			Keys = new Button[numKeys];
 			foreach (KeyCode keycode in Enum.GetValues(typeof(KeyCode)))
 			{
-				Keys[(int) keycode] = new ButtonState();
+				Keys[(int) keycode] = new Button();
 			}
 		}
 
@@ -50,7 +50,7 @@ namespace MoonWorks.Input
 			foreach (int keycode in Enum.GetValues(typeof(KeyCode)))
 			{
 				var keyDown = Marshal.ReadByte(keyboardState, keycode);
-				Keys[keycode] = Keys[keycode].Update(Conversions.ByteToBool(keyDown));
+				Keys[keycode].Update(Conversions.ByteToBool(keyDown));
 
 				if (Conversions.ByteToBool(keyDown))
 				{
@@ -86,9 +86,14 @@ namespace MoonWorks.Input
 			return Keys[(int) keycode].IsReleased;
 		}
 
-		public ButtonState ButtonState(KeyCode keycode)
+		public Button Button(KeyCode keycode)
 		{
 			return Keys[(int) keycode];
 		}
+
+		public ButtonState ButtonState(KeyCode keycode)
+		{
+			return Keys[(int) keycode].State;
+		}
 	}
 }

src/Math/MathHelper.cs

@@ -331,16 +331,36 @@ namespace MoonWorks.Math
 			return angle;
 		}
 
+		/// <summary>
+		/// Rescales a value within a given range to a new range.
+		/// </summary>
 		public static float Normalize(float value, short min, short max, short newMin, short newMax)
 		{
 			return ((value - min) * (newMax - newMin)) / (max - min) + newMin;
 		}
 
+		/// <summary>
+		/// Rescales a value within a given range to a new range.
+		/// </summary>
 		public static float Normalize(float value, float min, float max, float newMin, float newMax)
 		{
 			return ((value - min) * (newMax - newMin)) / (max - min) + newMin;
 		}
 
+		/// <summary>
+        /// Step from start towards end by change.
+        /// </summary>
+        /// <param name="start">Start value.</param>
+        /// <param name="end">End value.</param>
+        /// <param name="change">Change value.</param>
+        /// <returns>The final delta.</returns>
+        public static float Approach(float start, float end, float change)
+        {
+            return (start < end ?
+                System.Math.Min(start + change, end) :
+                System.Math.Max(start - change, end)) - start;
+        }
+
 		#endregion
 
 		#region Internal Static Methods