add very basic copies of System.Drawing classes to Gwen namespace

minimal implementation only, just enough to satisfy Gwen's usage of the original System.Drawing classes

Gwen/Color.cs

@@ -0,0 +1,65 @@
+using System;
+
+namespace Gwen
+{
+	[Serializable]
+	public struct Color
+	{
+		public byte A;
+		public byte R;
+		public byte G;
+		public byte B;
+
+		public static readonly Color White = FromArgb(255, 255, 255);
+		public static readonly Color Black = FromArgb(0, 0, 0);
+		public static readonly Color Red = FromArgb(255, 0, 0);
+		public static readonly Color Green = FromArgb(0, 255, 0);
+		public static readonly Color Blue = FromArgb(0, 0, 255);
+		public static readonly Color Yellow = FromArgb(255, 255, 0);
+
+		public static Color FromArgb(int red, int green, int blue)
+		{
+			return FromArgb(255, red, green, blue);
+		}
+
+		public static Color FromArgb(int alpha, int red, int green, int blue)
+		{
+			Color result;
+			result.A = (byte)alpha;
+			result.R = (byte)red;
+			result.G = (byte)green;
+			result.B = (byte)blue;
+			return result;
+		}
+
+		public float GetHue()
+		{
+			int r = R;
+			int g = G;
+			int b = B;
+			byte minval = (byte) Math.Min (r, Math.Min (g, b));
+			byte maxval = (byte) Math.Max (r, Math.Max (g, b));
+			
+			if (maxval == minval)
+				return 0.0f;
+			
+			float diff = (float)(maxval - minval);
+			float rnorm = (maxval - r) / diff;
+			float gnorm = (maxval - g) / diff;
+			float bnorm = (maxval - b) / diff;
+			
+			float hue = 0.0f;
+			if (r == maxval) 
+				hue = 60.0f * (6.0f + bnorm - gnorm);
+			if (g == maxval) 
+				hue = 60.0f * (2.0f + rnorm - bnorm);
+			if (b  == maxval) 
+				hue = 60.0f * (4.0f + gnorm - rnorm);
+			if (hue > 360.0f) 
+				hue = hue - 360.0f;
+			
+			return hue;
+		}
+	}
+}
+

Gwen/Point.cs

@@ -0,0 +1,20 @@
+using System;
+
+namespace Gwen
+{
+	[Serializable]
+	public struct Point
+	{
+		public int X;
+		public int Y;
+
+		public static readonly Point Empty;
+
+		public Point(int x, int y)
+		{
+			X = x;
+			Y = y;
+		}
+	}
+}
+

Gwen/Rectangle.cs

@@ -0,0 +1,56 @@
+using System;
+
+namespace Gwen
+{
+	[Serializable]
+	public struct Rectangle
+	{
+		public int X;
+		public int Y;
+		public int Width;
+		public int Height;
+
+		public static readonly Rectangle Empty;
+
+		public Rectangle(int x, int y, int width, int height)
+		{
+			X = x;
+			Y = y;
+			Width = width;
+			Height = height;
+		}
+
+		public int Left
+		{
+			get
+			{
+				return X;
+			}
+		}
+
+		public int Top
+		{
+			get
+			{
+				return Y;
+			}
+		}
+
+		public int Right
+		{
+			get
+			{
+				return X + Width;
+			}
+		}
+
+		public int Bottom
+		{
+			get
+			{
+				return Y + Height;
+			}
+		}
+	}
+}
+