fix graphics resources disposing out of order

src/Graphics/GraphicsDevice.cs

@@ -12,6 +12,8 @@ namespace MoonWorks.Graphics
 
         private readonly Queue<CommandBuffer> commandBufferPool;
 
+        private readonly List<WeakReference> resources = new List<WeakReference>();
+
         public GraphicsDevice(
             IntPtr deviceWindowHandle,
             Refresh.PresentMode presentMode,
@@ -78,16 +80,44 @@ namespace MoonWorks.Graphics
             Refresh.Refresh_Wait(Handle);
         }
 
+        internal void AddResourceReference(WeakReference resourceReference)
+        {
+            lock (resources)
+            {
+                resources.Add(resourceReference);
+            }
+        }
+
+        internal void RemoveResourceReference(WeakReference resourceReference)
+        {
+            lock (resources)
+            {
+                resources.Remove(resourceReference);
+            }
+        }
+
         protected virtual void Dispose(bool disposing)
         {
             if (!IsDisposed)
             {
                 if (disposing)
                 {
-                    // TODO: dispose managed state (managed objects)
+                    lock (resources)
+                    {
+                        foreach (var resource in resources)
+                        {
+                            var target = resource.Target;
+                            if (target != null)
+                            {
+                                (target as IDisposable).Dispose();
+                            }
+                        }
+                        resources.Clear();
                     }
 
                     Refresh.Refresh_DestroyDevice(Handle);
+                }
+
                 IsDisposed = true;
             }
         }

src/Graphics/GraphicsResource.cs

@@ -1,6 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Text;
 
 namespace MoonWorks.Graphics
 {
@@ -12,9 +10,14 @@ namespace MoonWorks.Graphics
         public bool IsDisposed { get; private set; }
         protected abstract Action<IntPtr, IntPtr> QueueDestroyFunction { get; }
 
+        private WeakReference selfReference;
+
         public GraphicsResource(GraphicsDevice device)
         {
             Device = device;
+
+            selfReference = new WeakReference(this);
+            Device.AddResourceReference(selfReference);
         }
 
         protected virtual void Dispose(bool disposing)
@@ -22,6 +25,13 @@ namespace MoonWorks.Graphics
             if (!IsDisposed)
             {
                 QueueDestroyFunction(Device.Handle, Handle);
+
+                if (selfReference != null)
+                {
+                    Device.RemoveResourceReference(selfReference);
+                    selfReference = null;
+                }
+
                 IsDisposed = true;
             }
         }