Question

I have several MeshGeometry3D elements that are stored in separate files. For example, somemodel.xml might contain <MeshGeometry3D ... />.

If I load them in the main UI thread, they lock up the UI while they load. So I’ve tried loading them in a separate thread:

ThreadStart threadStart = delegate
{
    var geometry = ConvertXmlFileToMeshGeometry3D(filename);
    viewport2DVisual3D.Dispatcher.BeginInvoke(
        DispatcherPriority.Normal,
        new Action(delegate { viewport2DVisual3D.Geometry = geometry; }));
};
threadStart.BeginInvoke(delegate(IAsyncResult aysncResult) { threadStart.EndInvoke(aysncResult); }, null);

However, this gives an exception on the line viewportVisual.Geometry = geometry;: The calling thread cannot access this object because a different thread owns it.

In other words, the MeshGeometry3D was created on a different thread, so I cannot make it the Viewport2DVisual3D‘s Geometry.

I can’t figure out a way to asynchronously load the MeshGeometry3Ds without them being owned by the wrong thread. Is this just something that is not possible, or is there a way to do it?

Edit: Profiling suggests that about 13% of the time to load a MeshGeometry3D is spent loading the xml element from the file (var element = XElement.Load(filename);), and the rest is spent converting it to a MeshGeometry3D:

return new MeshGeometry3D
{
    Normals = (Vector3DCollection)new Vector3DCollectionConverter().ConvertFromString(element.Attribute("Normals").Value),
    Positions = (Point3DCollection)new Point3DCollectionConverter().ConvertFromString(element.Attribute("Positions").Value),
    TextureCoordinates = (PointCollection)new PointCollectionConverter().ConvertFromString(element.Attribute("TextureCoordinates").Value),
    TriangleIndices = (Int32Collection)new Int32CollectionConverter().ConvertFromString(element.Attribute("TriangleIndices").Value),
};

So it doesn’t look like fetching the XML from disk is the bottleneck here.

Answer 1

Unless you need to modify the model later you can try to Freeze it after it has been loaded, then it can be shared accross threads, see Freezable Objects Overview.