Rough Notes on UWP and webRTC (Part 3)

This is a follow-on from my previous post around taking small steps with webRTC and UWP.

At the end of that post, I had some scrappy code which was fairly fixed in function in that it was a small UWP app which would use the UWP webRTC library to connect to a signalling service and then could begin a conversation with a peer that was also connected to the same signalling service.

The signalling service in question had to be the one provided with the UWP webRTC bits and the easiest way to test that my app was doing something was to run it against the PeerCC sample which also ships with the UWP webRTC bits and does way more than my app does by demonstrating lots of functionality that’s present in UWP webRTC.

The links to all the webRTC pieces that I’m referring to are in the previous 2 posts on this topic.

Tidying Up

The code that I had in the signalling branch of this github repo at the end of the previous post was quite messy and not really in a position to be re-used and so I spent a little time just pulling that code apart, refactoring some of the functionality behind interfaces and reducing the implicit dependencies in order to try and move the code towards being a little bit more re-usable (even if the functionality it currently implements isn’t of much actual use to a real user – I’m just experimenting).

What I was trying to move towards was some code that I knew sort of worked in this XAML based UWP app that I could then lift out of the app and re-use in a non-XAML based UWP app (i.e. a Unity app) so that I would have some control over the knowns and unknowns in trying out that process.

What I needed to do then was make sure that in refactoring things, I ended up with code that was clearly abstracted from its dependencies on anything in the XAML layer.

Firstly, I refactored the solution into two projects to make for a class library and an app project which referenced it;

image

and then I took some of the pieces of functionality that I had in there and abstracted it out into a set of interfaces;

image

with a view to making the dependencies between these interfaces explicit and the implementation pluggable.

This included putting the code which provides signalling by invoking the signalling service supplied with the original sample behind an interface. Note that I’m not at all trying to come up with a generic interface that could generally represent the notion of signalling in webRTC but, instead, I’m just trying to put an interface on to the existing signalling code that I took (almost) entirely from the PeerCC sample project in the UWP webRTC bits.

image

The other interfaces/services that I added here are hopefully named ‘reasonably well’ in terms of the functionality that they represent with perhaps the one that’s not quite so obvious obvious being the IConversationManager.

This interface is just my attempt to codify the minimum functionality that I need to bring the other interface implementations together in order to get any kind of conversation over webRTC up and running from my little sample app as it stands and that IConversationManager interface right now just looks as below;

image

and so the idea here is that a consumer of an IConversationManager can simply;

  • Tell the manager whether it is meant to initiate conversations or simply wait for a remote peer to being a conversation with it
    • In terms of initiating conversations – the code is ‘aggressive’ in that it simply finds the first peer that it sees provided by the signalling service and attempts to being a conversation with it.
  • Call InitialiseAsync providing the name that the local peer wants to be represented by.
  • Call ConnectToSignallingAsync with the IP Address and port where the signalling service is to be found.

From there, the implementation jumps in and tries to bring together all the right pieces to get a conversation flowing.

In making these abstractions, I found two places where I had to apply a little bit of thought and that was where;

  • The UWP webRTC pieces need initialising with a Dispatcher object and so I abstracted that out into an interface so that an implementation can be injected into the underlying layer.
  • There is a need at some point to do some work with UI objects to represent media streams. In the code to date, this has meant working with XAML MediaElements but in other scenarios (e.g. Unity UI) that wouldn’t work.

In order to try and abstract the library code from these media pieces, I made an IMediaManager interface with the intention being to write a different implementation for the different UI layers so to bring this library up inside of a Unity app I’d at least need to provide a Unity version of the highlighted implementation pieces below which are about IMediaManager in a XAML UI world;

image

My main project took a dependency on autofac to provide a container from which to serve up the implementations of my interfaces and I did a cheap trick of providing my own “container” embedded into the library and named CheapContainer in case the library was going to be used in a situation where autofac or some other IoC container wasn’t immediately available.

Configuration of the container then moves into my App.xaml.cs file and is fairly simple and I wrote it twice, once for autofac and once using my own CheapContainer;

#if !USE_CHEAP_CONTAINER
        Autofac.IContainer Container
        {
            get
            {
                if (this.iocContainer == null)
                {
                    this.BuildContainer();
                }
                return (this.iocContainer);
            }
        }
#endif
        void BuildContainer()
        {
#if USE_CHEAP_CONTAINER
            CheapContainer.Register<ISignallingService, Signaller>();
            CheapContainer.Register<IDispatcherProvider, XamlMediaElementProvider>();
            CheapContainer.Register<IXamlMediaElementProvider, XamlMediaElementProvider>();
            CheapContainer.Register<IMediaManager, XamlMediaElementMediaManager>();
            CheapContainer.Register<IPeerManager, PeerManager>();
            CheapContainer.Register<IConversationManager, ConversationManager>();
#else
            var builder = new ContainerBuilder();
            builder.RegisterType<Signaller>().As<ISignallingService>().SingleInstance();

            builder.RegisterType<XamlMediaElementProvider>().As<IXamlMediaElementProvider>().As<IDispatcherProvider>().SingleInstance();

            builder.RegisterType<XamlMediaElementMediaManager>().As<IMediaManager>().SingleInstance();
            builder.RegisterType<PeerManager>().As<IPeerManager>().SingleInstance();
            builder.RegisterType<ConversationManager>().As<IConversationManager>().SingleInstance();
            builder.RegisterType<MainPage>().AsSelf().SingleInstance();
            this.iocContainer = builder.Build();
#endif
        }
#if USE_CHEAP_CONTAINER
#else
        Autofac.IContainer iocContainer;
#endif

and the code which now lives inside of my MainPage.xaml.cs file involved in actually getting the webRTC conversation up and running is reduced down to almost nothing;

        async void OnConnectToSignallingAsync()
        {
            await this.conversationManager.InitialiseAsync(this.addressDetails.HostName);

            this.conversationManager.IsInitiator = this.isInitiator;

            this.HasConnected = await this.conversationManager.ConnectToSignallingAsync(
                this.addressDetails.IPAddress, this.addressDetails.Port);
        }

and so that seems a lot simpler, neater and more re-usable than what I’d had at the end of the previous blog post.

In subsequent posts, I’m going to see if I can now re-use this library inside of other environments (e.g. Unity) so as to bring this same (very limited) webRTC functionality that I’ve been playing with to that environment.

“Hello World” Mixed Reality Demo from the UK TechKnowDay Event 2018

I had the privilege to be invited to speak at the UK TechKnowDay Event today as part of International Women’s Day;

and I went along with my colleague, Pete, and talked to the attendees about Windows Mixed Reality.

As part of that, I’d put together a very simple “Hello World” demo involving taking a 3D model of an avatar who appeared when air-tapped on a HoloLens and then fell with a parachute to the floor. This is really just a way of showing the basics of using the Unity toolkit, the Mixed Reality Toolkit and Visual Studio to make something that runs on HoloLens and which blends the digital with the physical.

At the event, we shortened the demo because we were running a little low on time and so I promised to include the materials on the web somewhere and that’s what this post is about.

First, I made 3 models using Paint3D and so I wanted to include that little video here – it’s intended to be spoken over so there’s no audio on it;

and then there’s a little video showing me working through in Unity to bring in the assets from Paint3D and add some very, very limited interactivity to them using Unity and the Mixed Reality Toolkit.

The way the app is supposed to work is that an air tap will cause the creation of an instance of the avatar. She will then fall under (reduced) gravity landing on a surface when her parachute should disappear and then she might sort of ‘snowboard’ to a stop where her snowboard should also disappear Smile

I’m not sure that anyone would want this coding masterpiece Smile but if they did then it’s on github over here;

https://github.com/mtaulty/parachutes

Feel very free to re-use, share or whatever you like with this if it’s of use to you.

Baby Steps with Spatial Mapping in 2D and 3D Using XAML and SharpDX

NB: The usual blog disclaimer for this site applies to posts around HoloLens. I am not on the HoloLens team. I have no details on HoloLens other than what is on the public web and so what I post here is just from my own experience experimenting with pieces that are publicly available and you should always check out the official developer site for the product documentation.

I’ve been living in fear and hiding from a particular set of APIs Winking smile

Ever since HoloLens and Windows Mixed Reality first came along, I’ve been curious about the realities of the spatial mapping APIs and yet I’ve largely just treated them as a “black box”.

Naturally, that’s not to say that I haven’t benefitted from those APIs because I’ve been using them for many months in Unity via the Mixed Reality Toolkit and its support for spatial mapping and the prefab that’s fairly easy to drop into a Unity project as I first explored in this post last year;

Hitchhiking the HoloToolkit-Unity, Leg 3–Spatial Understanding (& Mapping)

That said, I’ve still had it on my “to do list” for a long time to visit these APIs a little more directly and that’s what this blog post is about.

It’s important to say that the post is mostly meant to be just “for fun” to give me a place to write down some explorations – I’m not planning to do an exhaustive write up of the APIs and what I’ll end up with by the end of this post is going to be pretty “rough”.

It’s also important to say that there are official documentation pages which detail a lot more than I’m about to write up in this post.

Spatial mapping

Spatial mapping in DirectX

but (as usual) I hadn’t really read those documents in nearly enough detail until I started to explore on my own for this post – it’s the exploration that drives the learning.

Additionally, there’s a great official sample that goes along with those documents;

Holographic Spatial Mapping Sample

but, again, I hadn’t actually seen this sample until I got well into writing this post and was trying to figure things out and I realised that I was largely trying to produce a much simpler, less functional piece of code which targeted a different type of application than the one in the sample but there are many similarities between where I ended up and that sample.

So, if you want the definitive views on these topics there are lots of links to visit.

In the meantime, I’m going to write up my own experiments here.

Choosing a Sandbox to Play In

Generally speaking, if I’m wanting to experiment with some .NET APIs then I write a console application. It seems the quickest, easiest thing to spin up.

In a Mixed Reality world, the equivalent seems to be a 2D XAML application. I find it is much quicker to Code->Deploy->Test->Debug when working on a 2D XAML application than when working on (e.g.) a 3D Unity application.

Of course, the output is then a 2D app rather than an immersive app but if you just want to test out some UWP APIs (which the spatial mapping APIs are) then that’s ok.

Specifically, in this case, I found that trying to make use of these APIs in a 2D environment seemed to actually be helpful to gaining some understanding of them as it stopped me from just looking for a quick Unity solution to various challenges and I definitely felt that I wasn’t losing anything by at least starting my journey inside of a 2D XAML application where I could quickly iterate.

Getting Going – Asking for Spatial Mapping API Access

I made a quick, blank 2D XAML UWP application in Visual Studio and made sure that its application manifest gave me the capability to use Spatial Mapping.

When I look in Visual Studio today, I don’t see this listed as an option in the UI and so I hacked the manifest file in the XML editor;

image

where uap2 translates as a namespace to;

xmlns:uap2=http://schemas.microsoft.com/appx/manifest/uap/windows10/2

in case you ever got stuck on that one. From there, I had a blank app where I could write some code to run on the Loaded event of my main XAML page.

Figuring out the SurfaceSpatialObserver

At this point, I had an idea of what I wanted to do and I was fairly sure that I needed to spin up a SpatialSurfaceObserver which does a lot of the work of trying to watch surfaces as they are discovered and refined by HoloLens.

The essence of the class would seem to be to check whether spatial mapping is supported and available via the IsSupported and RequestAccessAsync() methods.

Once support is ascertained, you define some “volumes” for the observer to observe for spatial mapping data via the SetBoundingVolume/s method and then you can interrogate that data via the GetObservedSurfaces method.

Additionally, there’s an event ObservedSurfacesChanged to tell you when the data relating to surfaces has changed because the device has added/removed or updated data.

This didn’t seem too bad and so my code for checking for support ended up looking as below;

  async void OnLoaded(object sender, RoutedEventArgs e)
    {
      bool tryInitialisation = true;

      if (Windows.Foundation.Metadata.ApiInformation.IsApiContractPresent(
          "Windows.Foundation.UniversalApiContract", 4, 0))
      {
        tryInitialisation = SpatialSurfaceObserver.IsSupported();
      }

      if (tryInitialisation)
      {
        var access = await SpatialSurfaceObserver.RequestAccessAsync();

        if (access == SpatialPerceptionAccessStatus.Allowed)
        {
          this.InitialiseSurfaceObservation();
        }
        else
        {
          tryInitialisation = false;
        }
      }
      if (!tryInitialisation)
      {
        var dialog = new MessageDialog(
          "Spatial observation is either not supported or not allowed", "Not Available");

        await dialog.ShowAsync();
      }
    }

Now, as far as I could tell the SpatialSurfaceObserver.IsSupported() method only became available in V4 of the UniversalApiContract so I’m trying to figure out whether it’s safe to call that API or not as you can see above before using it.

The next step would be perhaps to try and define volumes and so I ploughed ahead there…

Volumes, Coordinate Systems, Reference Frames, Locators – Oh My Winking smile

I wanted to keep things as simple as possible and so I chose to look at the SetBoundingVolume method which takes a single SpatialBoundingVolume and there are a number of ways of creating these based on Boxes, Frustrums and Spheres.

I figured that a sphere was a fairly understandable thing and so I went with a sphere and decided I’d use a 5m radius on my sphere hoping to determine all surface information within that radius.

However, to create a volume you first need a SpatialCoordinateSystem and the easiest way I found of getting hold of one of those was to get hold of a frame of reference.

Frames of reference can either be “attached” in the sense of being head-locked and following the device or they can be “stationary” where they don’t follow the device.

A stationary frame of reference seemed easier to think about and so I went that way but to get hold of a frame of reference at all I seemed to need to use a SpatialLocator which has a handy GetDefault() method on it and then I can use the CreateStationaryFrameOfReferenceAtCurrentLocation() method to create my frame.

So…my reasoning here is that I’m creating a frame of reference at the place where the app starts up and that it will never move during the app’s lifetime. Not perhaps the most “flexible” thing in the world, but it seemed simpler than any other options so I went with it.

With that in place, my “start-up” code looks as below;

  void InitialiseSurfaceObservation()
    {
      // We want the default locator.
      this.locator = SpatialLocator.GetDefault();

      // We try to make a frame of reference that is fixed at the current position (i.e. not
      // moving with the user).
      var frameOfReference = this.locator.CreateStationaryFrameOfReferenceAtCurrentLocation();

      this.baseCoordinateSystem = frameOfReference.CoordinateSystem;

      // Make a box which is centred at the origin (the user's startup location)
      // and is hopefully oriented to the Z axis and a certain width/height.
      var boundingVolume = SpatialBoundingVolume.FromSphere(
        this.baseCoordinateSystem,
        new SpatialBoundingSphere()
        {
          Center = new Vector3(0, 0, 0),
          Radius = SPHERE_RADIUS
        }
      );
      this.surfaceObserver = new SpatialSurfaceObserver();
      this.surfaceObserver.SetBoundingVolume(boundingVolume);
    }

Ok…I have got hold of a SpatialSurfaceObserver that’s observing one volume for me defined by a sphere. What next?

Gathering and Monitoring Surfaces Over Time

Having now got my SpatialSurfaceObserver with a defined volume, I wanted some class that took on the responsibility of grabbing any surfaces from it, putting them on a list and then managing that list as the observer fired events to flag that surfaces had been added/removed/updated.

In a real application, it’s likely that you’d need to do this in a highly performant way but I’m more interested in experimentation here than performance and so I wrote a small SurfaceChangeWatcher class which I can pass the SpatialSurfaceObserver to.

Surfaces are identified by GUID and so this watcher class maintains a simple Dictionary<Guid,SpatialSurfaceInfo>. On startup, it calls the GetObservedSurfaces method to initially populate its dictionary and then it handles the ObservedSurfacesChanged event to update its dictionary as data changes over time.

It aggregates up the changes that it sees and fires its own event to tell any interested parties about the changes.

I won’t post the whole source code for the class here but will just link to it instead. It’s not too long and it’s not too complicated.

Source SurfaceChangeWatcher.cs.

Checking for Surface Data

At this point, I’ve enough code to fire up the debugger and debug my 2D app on a HoloLens or an emulator and see if I can get some spatial mapping data into my code.

It’s worth remembering that the HoloLens emulator is good for debugging spatial mapping as by default the emulator places itself into a “default room” and it can switch to a number of other rooms provided with the SDK and also to custom rooms that have been recorded from a HoloLens.

So, debugging on the emulator I can see that in the first instances here I see 22 loaded surfaces coming back from the SpatialSurfaceObserver;

image

and you can see the ID for my first surface and the UpdateTime that it’s associated with.

I also notice that very early on in the application I see the ObservedSurfacesChanged event fire and my code in SurfaceChangeWatcher simply calls back into the LoadSurfaces method shown in the screenshot above which then attempts to figure out which surfaces have been added/removed or updated since they were last queried.

So, getting hold of the surfaces within a volume and responding to their changes as they evolve doesn’t seem too onerous.

But, how to get the actual polygonal mesh data itself?

Getting Mesh Data

Once you have hold of a SpatialSurfaceInfo, you can attempt to get hold of the SpatialSurfaceMesh which it represents via the TryComputeLatestMeshAsync method.

This method wants a “triangle density” in terms of how many triangles it should attempt to bring back per cubic metre. If you’ve used the Unity prefab then you’ll have seen this parameter before and in my code here I chose a value of 100 and stuck with it.

The method is also asynchronous and so you can’t just demand the mesh in realtime but it’s a fairly simple call and here’s a screenshot of me back in the debugger having made that call to get some data;

image

That screenshot shows that I’ve got a SpatialSurfaceMesh and it contains 205 vertices in the R16G16B16A16IntNormalized format and that there are 831 triangle vertices in an R16Uint format and it also gives me the Id and the UpdateTime of the SpatialSurfaceInfo.

It’s also worth noting the VertexPositionScale which needs to be applied to the vertices to reconstruct them.

Rendering Mesh Data

Now, at this point I felt that I had learned a few things about how to get hold of spatial mapping meshes but I thought that it wasn’t really “enough” if I didn’t make at least some attempt to render the meshes produced.

I thought about a few options around how I might do that given that I’m running code inside of a 2D XAML application.

I wondered whether I might somehow flatten the mesh and draw it with a XAML Canvas but that seemed unlikely and I suspected that the best road to go down would be to keep the data in the format that it was already being provided in and try and hand it over to DirectX for rendering.

That led me to wonder whether something from Win2D might be able to draw it for me but Win2D stays true to its name and doesn’t (as far as I know) get into the business of wrapping up Direct3D APIs.

So…I figured that I’d need to bite the bullet and see if I could bring this into my 2D app via the XAML SwapChainPanel integration element with some rendering provided by SharpDX.

It’s worth saying that I’ve hardly ever used SwapChainPanel and I’ve never used SharpDX before so I figured that putting them together with this mesh data might be “fun” Winking smile

A UWP SharpDX SwapChainPanel Sample

In order to try and achieve that, I went on a bit of a search to try and see if I could find a basic sample which illustrated how to integrate SharpDX code inside of a XAML application rendering to a SwapChainPanel.

It took me a little while to find that sample as quite a few of the SharpDX samples seem to be out of date these days and I asked around on Twitter before finding this great sample which uses SharpDX and SwapChainPanel to render a triangle inside of a UWP XAML app;

https://github.com/minhcly/UWP3DTest

That let me drop a few SharpDX packages into my project;

image

and the sample was really useful in that it enabled me to drop a SwapChainPanel into my XAML UI app and, using code that I lifted and reworked out of the sample, I could get that same triangle to render inside of my 2D XAML application.

That gave me a little hope that I might be able to get the mesh data rendered inside of my application too.

Building a SharpDX Renderer (or trying to!)

I wrote a class SwapChainPanelRenderer (source) which essentially takes the SwapChainPanel and my SurfaceChangeWatcher class and it puts them together in order to retrieve/monitor spatial meshes as they are produced by the SpatialSurfaceObserver.

The essence of that class is that it goes through a few steps;

  1. It Initialises D3D via SharpDX largely following the pattern from the sample I found.
  2. It creates a very simple vertex shader and pixel shader much like the sample does although I ended up tweaking them a little.
  3. Whenever a new SpatialSurfaceInfo is provided by the SurfaceChangeWatcher the renderer attempts asks the system to compute the mesh for it and creates a number of data structures from that mesh;
    1. A vertex buffer to match the format provided by the mesh
    2. An index buffer to match the format provided by the mesh
    3. A constant buffer with details of how to transform the vertices provided by the mesh
  4. Whenever the renderer is asked to render, it loads up the right vertex/index/constant buffers for each of the meshes that it knows about and asks the system to render them passing through a few transformation pieces to the vertex shader.

It’s perhaps worth noting a couple of things around how that code works – the first would be;

  • In order to get hold of the actual vertex data, this code relies on using unsafe C# code and IBufferByteAccess in order to be able to grab the real data buffers rather than copying it.

The second point that might be worth mentioning is that I spent quite a bit of time trying to see if I could get the mesh rendering right.

  • I’m not 100% there at the time of writing but what I have managed to get working has been done by consulting back with the official C++ sample which has a more complex pipeline but I specifically consulted it around how to make use of the SpatialSurfaceMesh.VertexPositionScale property and I tried to make my code line up with the sample code around that in as much as possible.

I must admit that I spent a bit of time staring at my code and trying to compare to the sample code as a way of trying to figure out if I could improve the way mine was seeming to render and I think I can easily spend more time on it to make it work better.

The last point I’d make is that there’s nothing in the code at the time of writing which attempts to align the HoloLens position, orientation and view with what’s being shown inside of the 2D app. What that means is;

  • The 2D app starts at a position (0,0.5,0) so half a metre above where the HoloLens is in the world.
  • The 2D app doesn’t know the orientation of the user so could be pointing in the wrong direction with respect to the mesh.

This can make the app a little “disorientating” unless you are familiar with what it’s doing Smile

Trying it Out

At the time of writing, I’ve mostly been trying this code out on the emulator but I have also experimented with it on HoloLens.

Here’s a screenshot of the official sample 3D app with its fancier shader running on the emulator where I’m using the “living room” room;

image

and here’s my 2D XAML app running in a window but, hopefully, rendering a similar thing albeit in wireframe;

image

and, seemingly, there’s something of a mirroring going on in there as well which I still need to dig into!

Wrapping Up & The Source

As I said at the start of the post, this one was very much just “for fun” but I thought I’d write it down so that I can remember it and maybe some pieces of it might be useful to someone else in the future.

If you want the source, it’s all over here on github so feel free to take it, play with it and feel very free to improve it Smile.