* Source/OpenTK/Platform/Egl/EglContext.cs:

* Source/OpenTK/Graphics/GraphicsContext.cs:
* Source/OpenTK/Graphics/IGraphicsContext.cs:
* Source/OpenTK/Platform/MacOS/AglContext.cs:
* Source/OpenTK/Platform/X11/X11GLContext.cs:
* Source/OpenTK/Graphics/GraphicsContextBase.cs:
* Source/OpenTK/Platform/Windows/WinGLContext.cs:
* Source/OpenTK/Platform/Dummy/DummyGLContext.cs: Added IsDisposed
  property to IGraphicsContext and implemented in all context classes.
  Removed 'bool disposed' fields from these classes in favor of the
  new property.

Source/OpenTK/Graphics/GraphicsContext.cs

@@ -301,13 +301,23 @@ namespace OpenTK.Graphics
         }
 
         /// <summary>
-        /// Gets a System.Boolean indicating whether this Context is current in the calling thread.
+        /// Gets a <see cref="System.Boolean"/> indicating whether this instance is current in the calling thread.
         /// </summary>
         public bool IsCurrent
         {
             get { return implementation.IsCurrent; }
         }
 
+        /// <summary>
+        /// Gets a <see cref="System.Boolean"/> indicating whether this instance has been disposed.
+        /// It is an error to access any instance methods if this property returns true.
+        /// </summary>
+        public bool IsDisposed
+        {
+            get { return disposed && implementation.IsDisposed; }
+            private set { disposed = value; }
+        }
+
         /// <summary>
         /// Gets or sets a value indicating whether VSync is enabled.
         /// </summary>
@@ -397,7 +407,7 @@ namespace OpenTK.Graphics
 
         void Dispose(bool manual)
         {
-            if (!disposed)
+            if (!IsDisposed)
             {
                 Debug.Print("Disposing context {0}.", (this as IGraphicsContextInternal).Context.ToString());
                 lock (context_lock)
@@ -410,7 +420,7 @@ namespace OpenTK.Graphics
                     if (implementation != null)
                         implementation.Dispose();
                 }
-                disposed = true;
+                IsDisposed = true;
             }
         }
 

Source/OpenTK/Graphics/GraphicsContextBase.cs

@@ -37,6 +37,8 @@ namespace OpenTK.Graphics
     {
         #region Fields
 
+        bool disposed;
+        
         protected ContextHandle Handle;
         protected GraphicsMode Mode;
 
@@ -50,6 +52,12 @@ namespace OpenTK.Graphics
 
         public abstract bool IsCurrent { get; }
 
+        public bool IsDisposed
+        {
+            get { return disposed; }
+            protected set { disposed = value; }
+        }
+        
         public abstract bool VSync { get; set; }
 
         public virtual void Update(IWindowInfo window) { }

Source/OpenTK/Graphics/IGraphicsContext.cs

@@ -31,10 +31,16 @@ namespace OpenTK.Graphics
         void MakeCurrent(IWindowInfo window);
 
         /// <summary>
-        /// Gets or sets a System.Boolean indicating whether the GraphicsContext is current in the calling thread.
+        /// Gets a <see cref="System.Boolean"/> indicating whether this instance is current in the calling thread.
         /// </summary>
         bool IsCurrent { get; }
 
+        /// <summary>
+        /// Gets a <see cref="System.Boolean"/> indicating whether this instance has been disposed.
+        /// It is an error to access any instance methods if this property returns true.
+        /// </summary>
+        bool IsDisposed { get; }
+
         /// <summary>
         /// Gets or sets a value indicating whether VSyncing is enabled.
         /// </summary>

Source/OpenTK/Platform/Dummy/DummyGLContext.cs

@@ -89,7 +89,7 @@ namespace OpenTK.Platform.Dummy
 
         #region --- IDisposable Members ---
 
-        public override void Dispose() { }
+        public override void Dispose() { IsDisposed = true; }
 
         #endregion
     }

Source/OpenTK/Platform/Egl/EglContext.cs

@@ -40,7 +40,6 @@ namespace OpenTK.Platform.Egl
         EglWindowInfo WindowInfo;
         EGLContext HandleAsEGLContext { get { return new EGLContext(Handle.Handle); } set { Handle = new ContextHandle(value.Handle.Value); } }
         bool vsync = true;   // Default vsync value is defined as 1 (true) in EGL.
-        bool disposed = false;
 
         #endregion
 
@@ -141,7 +140,7 @@ namespace OpenTK.Platform.Egl
         // thread?
         void Dispose(bool manual)
         {
-            if (!disposed)
+            if (!IsDisposed)
             {
                 if (manual)
                 {
@@ -152,7 +151,7 @@ namespace OpenTK.Platform.Egl
                 {
                     Debug.Print("[Warning] {0}:{1} was not disposed.", this.GetType().Name, HandleAsEGLContext.Handle);
                 }
-                disposed = true;
+                IsDisposed = true;
             }
         }
 

Source/OpenTK/Platform/MacOS/AglContext.cs

@@ -335,8 +335,7 @@ namespace OpenTK.Platform.MacOS
 
         void Dispose(bool disposing)
         {
-            
+            if (IsDisposed || Handle.Handle == IntPtr.Zero)
-            if (Handle.Handle == IntPtr.Zero)
                 return;
 
             Debug.Print("Disposing of AGL context.");
@@ -370,6 +369,8 @@ namespace OpenTK.Platform.MacOS
             {
                 throw new MacOSException((OSStatus)Agl.GetError(), Agl.ErrorString(Agl.GetError()));
             }
+
+            IsDisposed = true;
         }
 
         #endregion

Source/OpenTK/Platform/Windows/WinGLContext.cs

@@ -32,8 +32,6 @@ namespace OpenTK.Platform.Windows
 
         bool vsync_supported;
 
-        bool disposed;
-
         #region --- Contructors ---
 
         static WinGLContext()
@@ -305,7 +303,7 @@ namespace OpenTK.Platform.Windows
 
         private void Dispose(bool calledManually)
         {
-            if (!disposed)
+            if (!IsDisposed)
             {
                 if (calledManually)
                 {
@@ -316,7 +314,7 @@ namespace OpenTK.Platform.Windows
                     Debug.Print("[Warning] OpenGL context {0} leaked. Did you forget to call IGraphicsContext.Dispose()?",
                         Handle.Handle);
                 }
-                disposed = true;
+                IsDisposed = true;
             }
         }
 

Source/OpenTK/Platform/X11/X11GLContext.cs

@@ -26,8 +26,6 @@ namespace OpenTK.Platform.X11
         bool glx_loaded;
         GraphicsMode graphics_mode;
 
-        bool disposed;
-
         #region --- Constructors ---
 
         public X11GLContext(GraphicsMode mode, IWindowInfo window, IGraphicsContext shared, bool direct,
@@ -298,7 +296,7 @@ namespace OpenTK.Platform.X11
 
         private void Dispose(bool manuallyCalled)
         {
-            if (!disposed)
+            if (!IsDisposed)
             {
                 if (manuallyCalled)
                 {
@@ -312,7 +310,7 @@ namespace OpenTK.Platform.X11
                 {
                     Debug.Print("[Warning] {0} leaked.", this.GetType().Name);
                 }
-                disposed = true;
+                IsDisposed = true;
             }
         }