Fix crash in XAML design mode (#7)

* Add xaml design mode check

* updated packages

* Add IsDesignMode property for all controls

* make IsDesignMode as inline method.

* recovery xaml file to preview commit

* modify grammar

OpenTkControl/OpenTkControl.csproj

@@ -34,7 +34,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="OpenTK, Version=2.0.0.0, Culture=neutral, PublicKeyToken=bad199fe84eb3df4, processorArchitecture=MSIL">
-      <HintPath>..\packages\OpenTK.2.0.0\lib\net20\OpenTK.dll</HintPath>
+      <HintPath>..\..\packages\OpenTK.2.0.0\lib\net20\OpenTK.dll</HintPath>
     </Reference>
     <Reference Include="PresentationCore" />
     <Reference Include="PresentationFramework" />

OpenTkControl/OpenTkControlBase.xaml.cs

@@ -2,6 +2,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Windows;
@@ -305,6 +306,12 @@ public Task RequestRepaint()
             return tcs.Task;
         }
 
+        /// <summary>
+        /// Check if it is run in designer mode.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        protected bool IsDesignMode() => DesignerProperties.GetIsInDesignMode(this);
+
         /// <summary>
         /// Renders a screenshot of the frame with the specified dimensions. It will be in bgra format with
         /// [0,0] at the bottom left corner. Note that this is not meant for taking screenshots of what is
@@ -334,6 +341,11 @@ public Task<uint[,]> Screenshot(int width = 0, int height = 0)
         /// <param name="args">Information about the event</param>
         protected virtual void OnLoaded(object sender, RoutedEventArgs args)
         {
+#if DEBUG
+            if (IsDesignMode())
+                return;
+#endif
+
             _windowInfo = Utilities.CreateWindowsWindowInfo(
                 new WindowInteropHelper(Window.GetWindow(this)).Handle);
         }

OpenTkControl/ThreadOpenTkControl.cs

@@ -53,6 +53,7 @@ protected override void OnLoaded(object sender, RoutedEventArgs args)
             base.OnLoaded(sender, args);
 
             _endThreadCts = new CancellationTokenSource();
+
             _renderThread = new Thread(RenderThread)
             {
                 IsBackground = true,
@@ -89,6 +90,12 @@ private void OnIsVisibleChanged(object sender, DependencyPropertyChangedEventArg
         /// <param name="boxedToken"></param>
         private void RenderThread(object boxedToken)
         {
+#if DEBUG
+            // Don't render in design mode to prevent errors from calling OpenGL API methods.
+            if (Dispatcher.Invoke(() => IsDesignMode()))
+                return;
+#endif
+
             CancellationToken token = (CancellationToken) boxedToken;
 
             InitOpenGl();

OpenTkControl/UiOpenTkControl.cs

@@ -1,4 +1,5 @@
 using System;
+using System.ComponentModel;
 using System.Threading.Tasks;
 using System.Windows;
 using System.Windows.Media;
@@ -47,6 +48,12 @@ protected override void OnUnloaded(object sender, RoutedEventArgs routedEventArg
         /// <param name="args">The event arguments about this event</param>
         private void CompositionTargetOnRendering(object sender, EventArgs args)
         {
+#if DEBUG
+            //We needn't call render() for avoiding crash by calling OpenGL API methods.
+            if (IsDesignMode())
+                return;
+#endif
+
             DateTime now = DateTime.Now;
             if ((_continuous && now > _nextRenderTime) || ManualRepaintEvent.WaitOne(0))
             {