Make Perspex.Cairo compile again.

Cairo/Perspex.Cairo/CairoPlatform.cs

@@ -38,7 +38,7 @@ namespace Perspex.Cairo
             //return new BitmapImpl(imagingFactory, width, height);
         }
 
-        public IRenderer CreateRenderer(IntPtr handle, double width, double height)
+        public IRenderer CreateRenderer(IPlatformHandle handle, double width, double height)
         {
             return new Renderer(handle, width, height);
         }

Cairo/Perspex.Cairo/Renderer.cs

@@ -7,29 +7,31 @@
 namespace Perspex.Cairo
 {
     using System;
-    using Perspex.Platform;
-    using Splat;
-    using global::Cairo;
     using System.Runtime.InteropServices;
+    using global::Cairo;
     using Perspex.Cairo.Media;
+    using Perspex.Platform;
     using Matrix = Perspex.Matrix;
 
+    /// <summary>
+    /// A cairo renderer.
+    /// </summary>
     public class Renderer : IRenderer
     {
         /// <summary>
         /// The handle of the window to draw to.
         /// </summary>
-        private IntPtr hwnd;
+        private IPlatformHandle handle;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Renderer"/> class.
         /// </summary>
-        /// <param name="hwnd">The window handle.</param>
+        /// <param name="handle">The window handle.</param>
         /// <param name="width">The width of the window.</param>
         /// <param name="height">The height of the window.</param>
-        public Renderer(IntPtr hwnd, double width, double height)
+        public Renderer(IPlatformHandle handle, double width, double height)
         {
-            this.hwnd = hwnd;
+            this.handle = handle;
         }
 
         /// <summary>
@@ -38,7 +40,7 @@ namespace Perspex.Cairo
         /// <param name="visual">The visual to render.</param>
         public void Render(IVisual visual)
         {
-            using (var surface = new Win32Surface(GetDC(this.hwnd)))
+            using (var surface = CreateSurface(this.handle))
             using (DrawingContext context = new DrawingContext(surface))
             {
                 this.Render(visual, context);
@@ -52,11 +54,32 @@ namespace Perspex.Cairo
         /// <param name="height">The new height.</param>
         public void Resize(int width, int height)
         {
+            // Don't need to do anything here as we create a new Win32Surface on each render.
         }
 
         [DllImport("user32.dll")]
         private static extern IntPtr GetDC(IntPtr hWnd);
 
+        /// <summary>
+        /// Creates a cairo surface that targets a platform-specific resource.
+        /// </summary>
+        /// <param name="handle">The platform-specific handle.</param>
+        /// <returns>A surface.</returns>
+        private static Surface CreateSurface(IPlatformHandle handle)
+        {
+            switch (handle.HandleDescriptor)
+            {
+                case "HWND":
+                    return new Win32Surface(GetDC(handle.Handle));
+                case "HDC":
+                    return new Win32Surface(handle.Handle);
+                default:
+                    throw new NotSupportedException(string.Format(
+                        "Don't know how to create a Cairo renderer from a '{0}' handle",
+                        handle.HandleDescriptor));
+            }
+        }
+
         /// <summary>
         /// Renders the specified visual.
         /// </summary>