13 July 2018

Calculate Mixed Reality object locations on top or in front of obstructions using BoxCastAll

Intro

It was quite difficult to name this article. Usually I try to find a title that more or less describes a good search term that I used myself when I was looking for ‘something like this’, but I could not really find what I was looking for. What I have here is code that calculates locations for objects to be in front or on top of other objects and/or the Spatial Mesh. It does so using a BoxCastAll, something I have tried to use before, but not very successfully.  I have tried using Rigidbody.SweepTest and although it works for some scenarios, it did not work for all. My floating info screens ended up half a mountain anyway (in Walk the World), or the airport could not move over the ground because of some tiny obstacle blocking it (in AMS HoloATC). So I tried a new approach.

This is part one of a two-post blog post. Explaining how the BoxCast works and what extra tricks and calculations were necessary to get it to work properly proved to need quite a long text, so I will leave the behaviour actually using this code in good way for the next post.

BoxCast magic

So what is a BoxCast, actually? It’s comparable to a normal RayCast. But where a RayCast gives you the intersection of a line and an obstruction, a BoxCast does that – suprise - with a box. You essentially throw a box from a point along a vector until it hits something – or some things, as a BoxCastAll potentially returns more than one hit. If you take the one that is closest to your camera (a hit has a convenient “distance” property) you potentially have a place where you can place the object.

… except that it does not take into account the following things:

  • An object’s (center) position and the center of it’s bounding box are not always the same; this will make the BoxCast not always happen at the place you think it does
  • The vector from the camera to the hit may or may not be parallel to the direction of the BoxCast; therefore, we need to project the vector from the camera to the hit on the vector of the BoxCast.
  • The BoxCast hit detection happens at the edge of the casted box, and an objects position is determined by it’s center – so, we need so we need to move back a little towards the camera, or else about half of our object – determined by it’s actual orientation - will end up inside the obstruction.

My code takes all of that into account. It was quite hard won knowledge before I uncovered all the lovely pitfalls.

First a new utility method

For a BoxCast to work, you need a box. You typically accomplish that by getting the bounds of all the Renderers in the object you want to cast and combine those to one big bounding box. I hate typing or copying code more than once, so I create this little extension method to GameObject

public static class GameObjectExtensions
{
    public static Bounds GetEncapsulatingBounds(this GameObject obj)
    {
        Bounds totalBounds = new Bounds();

        foreach (var renderer in obj.GetComponentsInChildren<Renderer>())
        {
            if (totalBounds.size.magnitude == 0f)
            {
                totalBounds = renderer.bounds;
            }
            else
            {
                totalBounds.Encapsulate(renderer.bounds);
            }
        }

        return totalBounds;
    }
}

BoxCast Magic

In LookingDirectionHelpers, a static class containing utilities to calculate directions and places the direction the user is looking (duh) at I have created a method that does the BoxCast magic. It does quite a lot, and I am going through it step by step. It starts like this:

public static Vector3 GetObjectBeforeObstruction(GameObject obj, float maxDistance = 2,
    float distanceFromObstruction = 0.02f, int layerMask = Physics.DefaultRaycastLayers,
    BaseRayStabilizer stabilizer = null, bool showDebugLines = false)
{
    var totalBounds = obj.GetEncapsulatingBounds();

    var headRay = stabilizer != null
        ? stabilizer.StableRay
        : new Ray(CameraCache.Main.transform.position, CameraCache.Main.transform.forward);

     var hits = Physics.BoxCastAll(GetCameraPosition(stabilizer),
                                  totalBounds.extents, headRay.direction,
                                  Quaternion.identity, maxDistance, layerMask)
                                  .Where(h => !h.transform.IsChildOf(obj.transform)).ToList();

As you can see, the method accepts quite some parameters, most of them optional:

  • obj – the actual object to cast and place against or on top of the obstruction
  • maxDistance – the maximum distance to place the object from the camera (if it does not hit another object first)
  • distanceFromObstruction – the distance to keep between the object and the obstruction
  • layerMask – what layers should we ‘hit’ when we are looking for obstructions (default is everything)
  • stabilizer – used to get a more stable location and viewpoint source than the camera itself
  • showDebugLines – use some awesome help classes I nicked from the Unity Forums from “HiddenMonk” to show how the BoxCast is performed. Without these, I sure as hell would not have been able to identify all issues that I had to address.

Well then – first we get the total encapsulating bounds, then we check if we can either use the Stabilizer that we need to use the camera to define a ray in the direction we want to cast. The we calculate a point dead ahead of the camera – this is the.

And then we do the actual BoxCast, or actually a BoxCastAll. The cast is done:

  • From the Camera position
  • Using the total extents of the object
  • In the direction of the viewing ray (so a line from your head to where the gaze cursor is)
  • using no rotation (we used the Render's bounds, that already takes any rotation into account)
  • over a maximum distance
  • against the layers described by the layer mask (default is all)

Notice the Where clause at the end. BoxCasts hit everything, including child objects of the cast object itself, as it may be in the path of it’s own cast. So we need to weed out any hits that apply to the object itself or its children.

The next piece of visualizes how the BoxCast is performed, using HiddenMonk's code:

if (showDebugLines)
{
    BoxCastHelper.DrawBoxCastBox(GetCameraPosition(stabilizer),
        totalBounds.extents, headRay.direction,
        Quaternion.identity, maxDistance, Color.green);
}

This uses Debug.Draw – these lines are only visible in the Unity editor, in Play mode. They will not show up in the Game pane but in the Scene pane. Which makes sense, as you can them look at the result from every angle without affecting the actual scene in the game.

This looks like this:

image

Now to address the issues I listed on top of this article, we need to do a few things.

Giving it the best shot cast

The next line is a weird one but is explained by the fact that there may be a difference between the center of the actual bounding box (and thus the cast) and center of the object as reported by Unity. I am not entirely sure why this is, but trust me, it's happens with some objects. We need to compensate for that.

var centerCorrection = obj.transform.position - totalBounds.center;

Below you see an example of such an object. I typically happens when an object is composed of one or more other objects that are off center, and especially when the object is asymmetrical. Like this 'floating screen'. You will see it's an empty game object containing a Quad and a 3DTextPrefab that are moved upwards in local space. Without the correction factor, you get the situation on the left - the BoxCast happens 'too low'

imageimage

On the right side, you see the the desired effect. I opted to change the location to of the object to the center of the BoxCast – you might also consider changing the start location of the BoxCast, but that a side effect: the ray won’t start at the user’s viewpoint (but in this case, a little bit above it) which might be confusing or produce undesirable results.

Hit or miss - projection

We need to find the closest hit… but that hit might not be right in front us, along the viewing vector. So  we need to create a vector from the camera to the hit, then make a (longer) vector that follows the user’s gaze, and finally project the ‘hit vector’ to the ‘gaze vector’. Then and only then we know how much room there is in front of us.

if (hits.Any())
{
    var closestHit = hits.First(p => p.distance == hits.Select(q => q.distance).Min());
    var hitVector = closestHit.point - GetCameraPosition(stabilizer);
    var gazeVector = CalculatePositionDeadAhead(closestHit.distance * 2) - 
                       GetCameraPosition(stabilizer);
    var projectedHitVector = Vector3.Project(hitVector, gazeVector);

To show what happens, I have made a screenshot where I made Unity draw debug lines for every calculated vector:

if (showDebugLines)
{
    Debug.DrawLine(GetCameraPosition(stabilizer), closestHit.point, Color.yellow);
    Debug.DrawRay(GetCameraPosition(stabilizer), gazeVector, Color.blue);
    Debug.DrawRay(GetCameraPosition(stabilizer), projectedHitVector, Color.magenta);
}

Which results in the following view (for clarity I have disabled the code that draws the BoxCast for this screenshot)

image

A little magnification shows the area of interest a little bit better:

image

You can clearly see the the yellow line from the camera to the original hit, the blue line which is the viewing direction of the user, and the magenta line projected on that.

Keep your distance please

Now this all works fine for a flat object like a Quad (posing as an 'info screen' here. But not on a box like this for instance (which I made partially translucent for clarity).

image

The issue here is simple, although it took me some time to figure out what was causing it. Like I said before, the hit takes place at the edge of the shape, but the object's position is tied to it's center, so if I set the object's position to that hit, it will end up halfway the obstruction. QED.

So what we need to do is make yet another ray, that will go from the center of the object to the edge, following the same direction as the projected hit vector (the magenta line). Now RayCasts don't work from inside an object, but fortunately there's another way - the Bounds class supports an IntersectRay method. It works a bit kludgy IMHO but it does the trick:

var edgeRay = new Ray(totalBounds.center, projectedHitVector);
float edgeDistance;
if(totalBounds.IntersectRay(edgeRay,  out edgeDistance))
{
    if (showDebugLines)
    {
        Debug.DrawRay(totalBounds.center, 
            projectedHitVector.normalized * Mathf.Abs(edgeDistance + distanceFromObstruction),
            Color.cyan);
    }
}

So we intersect the projected hit vector from the center of the bounds to the edge of the bounds. This will give us the distance from the center to the part of the object that hit the obstruction, and we can move the object 'backwards' to the desired position. Since I specified a 'distanceFromObstruction' we can add that to the distance the object needs to be moved 'back'  as well to keep a distance from an obstruction, in stead of touching it (although for this object it's 0). Yet another debug line, cyan this time, shows what's happening:

image

The cyan line is the part over which the object is moved back. Now the only thing left is to calculate the new position and return it, this time using the centerCorrection we used before to make the object actually appear within the BoxCast's 'outlines':

return GetCameraPosition(stabilizer) +
            projectedHitVector - projectedHitVector.normalized * 
Mathf.Abs(edgeDistance + distanceFromObstruction) + centerCorrection;

Nobody is perfect

If you think "hey, it looks like it is not completely perfectly aligned", you are right. This is because Unity has it's limits in determining volumes and bounding boxes. This is probably because the main concern of a game is performance, not 100% accuracy. If I add this line to the code

BoxCastHelper.DrawBox(totalBounds.center, totalBounds.extents, Quaternion.identity, Color.red);

it actually shows the bounding box:

image

So this explains a bit more what is going on. With all the debug lines enabled it looks like this, which I can imagine is as confusing as helpful ;)

image

Show and tell

It’s actually not really easy to properly show you how this method can be utilized. As I said in the beginning, I will save that for the next post. In the mean time, I have cobbled together a demo project that uses the GetObjectBeforeObstruction in a very simple way. I have created a SimpleKeepInViewController that polls every so many seconds (2 is default) where the user looks, then calls GetObjectBeforeObstruction and moves the object there. This gives a bit of a nervous result, but you get the idea.

public class SimpleKeepInViewController : MonoBehaviour
{
    [Tooltip("Max distance to display object before user")]
    public float MaxDistance = 2f;

    [Tooltip("Distance before the obstruction to keep the current object")]
    public float DistanceBeforeObstruction = 0.02f;

    [Tooltip("Layers to 'see' when detecting obstructions")]
    public int LayerMask = Physics.DefaultRaycastLayers;

    [Tooltip("Time before calculating a new position")]
    public float PollInterval = 2f;

    [SerializeField]
    private BaseRayStabilizer _stabilizer;

    [SerializeField]
    private bool _showDebugBoxcastLines = true;

    private float _lastPollTime;


    void Update()
    {
        if (Time.time > _lastPollTime)
        {
            _lastPollTime = Time.time + PollInterval;
            LeanTween.move(gameObject, GetNewPosition(), 0.5f).setEaseInOutSine();
        }
#if UNITY_EDITOR
        if (_showDebugBoxcastLines)
        {
            LookingDirectionHelpers.GetObjectBeforeObstruction(gameObject, MaxDistance,
                DistanceBeforeObstruction, LayerMask, _stabilizer, true);
        }
#endif
    }

    private Vector3 GetNewPosition()
    {
        return LookingDirectionHelpers.GetObjectBeforeObstruction(gameObject, MaxDistance,
            DistanceBeforeObstruction, LayerMask, _stabilizer);
    }
}

There is only one oddity here – you see I actually call GetObjectBeforeObstruction twice. But the first time only happens in the editor, and only if you select the Show Debug Boxcast Line checkbox:

imageIf I did not add this, you would see the lines flash for one frame every 2 seconds, which is hardly enlightening. This way, you can see them all the time in the editor



imageIn the demo project you will find three objects – in the images above you have already seen a single block (the default), a rotating ‘info screen’ that shows “Hello World” and there’s also this composite object on the left (two cubes off-center), here displayed with all debug lines enabled ;). You can toggle between the three objects by saying “Toggle” or by pressing the “T”. The latter will actually also work in a HoloLens if you have a Bluetooth keyboard attached - and believe me, I tried ;-)


Conclusion

Yet another way to make an object appear next to on on top of an obstruction ;). This code actually took me way too much time to complete, but I learned a lot from it and at some point it became a matter of honor to get the bloody thing to work.

Fun factoid: most of the code, and a big part of the blog post, was actually written on train trips to an from an awesome HoloLens project I am currently involved in. Both the demo project and this blog post were actually published while being on my way, courtesy of the Dutch Railways free WiFi service ;)

13 June 2018

Measuring user movement in Mixed Reality apps

Intro

For a business HoloLens app I am currently developing - as well as for my app Walk the World - I needed a way to see if a user is moving or rotating in excess of a certain speed, to make certain control elements that are floating in view disappear when he/she is on the move - and come back when the movement stops. How this is used in detail I will describe later, but first I want to describe an easy helper behaviour to sample and measure speed, movement and rotation.

The actual tracker

using HoloToolkit.Unity;
using UnityEngine;

namespace HoloToolkitExtensions.Utilities
{
    public class CameraMovementTracker : Singleton<CameraMovementTracker>
    {
        [SerializeField]
        private readonly float _sampleTime = 1.0f;
        
        private Vector3 _lastSampleLocation;
        private Quaternion _lastSampleRotation;
        private float _lastSampleTime;

        public float Speed { get; private set; }
        public float RotationDelta { get; private set; }
        public float Distance { get; private set; }

        void Start()
        {
            _lastSampleTime = Time.time;
            _lastSampleLocation = CameraCache.Main.transform.position;
            _lastSampleRotation = CameraCache.Main.transform.rotation;
        }
   }
}

The behaviour is implemented as a Singleton. Although that is not strictly necessary, it makes sense to do so as there can also be only one Mixed Reality Camera and there is only one user. There is only one public property - that is the sample time. The idea of a sample time is simple - if you want to measure speed, or rotation, or movement - you have to do so over time. Default it samples location and rotation every second, and then it's up to you to decide to do something with it. At the start, it simply sets the sample time at now, the first sample location to the camera's current location and the rotation to it's current rotation.

In the update method (called every 60th of a second) we simply check whether the sample time period has expired, and then we get a new sample of location and rotation

void Update()
{
    if (Time.time - _lastSampleTime > _sampleTime)
    {
        Speed = CalculateSpeed();
        RotationDelta = CalculateRotation();
        Distance = CalculateDistanceCovered();
        _lastSampleTime = Time.time;
        _lastSampleLocation = CameraCache.Main.transform.position;
        _lastSampleRotation = CameraCache.Main.transform.rotation;
    }
}

The calculations itself are rather simple:

private float CalculateDistanceCovered()
{
    return Vector3.Distance(_lastSampleLocation, CameraCache.Main.transform.position);
}

private float CalculateSpeed()
{
    // return speed in km/h
    return CalculateDistanceCovered() / (Time.time - _lastSampleTime) * 3.6f;
}

private float CalculateRotation()
{
    return Mathf.Abs(Quaternion.Angle(_lastSampleRotation, 
CameraCache.Main.transform.rotation)); }

The distance is simply the difference between the previous and the current Camera position. Time.time is always in seconds since the app started, so dividing the speed through the elapsed time results in the speed in meters per second. Multiplying it by 3.6 makes that km/h - I presumed that to be a unit most people have a feeling for. Feel free to adapt this to your needs and have it return miles, yards, feet, furlongs, stadia or your outdated/obscure distance unit of choice ;).

So what is this good for?

Well, simply put - to take action when some threshold for rotation or movement is crossed.Like I mentioned, it's particularly useful for determining if control elements that should be more or less in the user's field of view should be moved - but not too often or too brusque, or else it is not possible to properly view or interact with them. In the demo project I have created a little demo behaviour that shows speed, distance covered and rotation in a floating text, and it also uses that data to decide whether or not it's time to move the text back into view.

image

This is a picture of the text just after it moving back in view. It will rapidly go back to showing all zeroes as it only measures these values over the last second.

The demo behaviour in a bit more detail:

using HoloToolkitExtensions.Utilities;
using UnityEngine;

public class ShowCameraActions : MonoBehaviour
{
    private TextMesh _mesh;

    [SerializeField]
    private float _rotationThreshold = 10f;

    [SerializeField]
    private float _moveTreshold = 0.4f;

    [SerializeField]
    private float _moveTime = 0.2f;

    private bool _isBusy;

    void Start()
    {
        _mesh = GetComponentInChildren<TextMesh>();
        MoveText();
    }

    void Update()
    {
        SetText();
        if ((CameraMovementTracker.Instance.RotationDelta > _rotationThreshold ||
            CameraMovementTracker.Instance.Distance > _moveTreshold ) && !_isBusy)
        {
            MoveText();
        }
    }

    private void MoveText()
    {
        _isBusy = true;
        LeanTween.move(gameObject, 
                        LookingDirectionHelpers.CalculatePositionDeadAhead(), _moveTime).
                  setEaseInOutSine().setOnComplete(() => _isBusy = false);
    }

    private void SetText()
    {
        var text = 
            string.Format(
"Speed: {0:00.00} km/h - Rotation: {1:000.0}° - Moved {2:00.0}m", CameraMovementTracker.Instance.Speed, CameraMovementTracker.Instance.RotationDelta, CameraMovementTracker.Instance.Distance); if (_mesh.text != text) { _mesh.text = text; Debug.Log(text); } } }

Long story short:

  • The text will be updated in every call to Update (which is 60 times per second) but since the CameraMovementTracker updates itself only once a second by default you should see the text change only once a second. I have also included a Debug.Log so you can see the numbers change when the text is still outside of your view. This of course only works in the Unity editor.
  • If the rotation threshold (10 degrees) or movement threshold (0.4 meters) is exceeded, the behaviour will attempt to move the text back into view (if it is not already doing so), using good old LeanTween. The "setEaseInOutSine" will make the movement start and stop fluently.

Conclusion

It's not hard to measure these things and the code is not complicated, but as is my custom - if I need to make something the 3rd time, it's time to make it into a generalized reusable class. And there you have it. Have fun with the demo project.

30 May 2018

Simple way to prevent an unintended double tap in Mixed Reality apps

This is an easy and simple tip, but one that I use in almost every Mixed Reality app at one point. It’s mostly applicable to HoloLens: especially new users tend to double (triple, or even more) tap when the are operating an app, because the gestures are new. This can lead to undesirable and confusing results, especially with toggles. So it can help a little to ‘dampen out’ those double clicks.

I created this very simple helper class called DoubleClickPreventer:

using UnityEngine;

namespace HoloToolkitExtensions.Utilities
{
    public class DoubleClickPreventer
    {
        private readonly float _clickTimeOut;

        private float _lastClick;

        public DoubleClickPreventer(float clickTimeOut = 0.1f)
        {
            _clickTimeOut = clickTimeOut;
        }

        public bool CanClick()
        {
            if (!(Time.time - _lastClick < _clickTimeOut))
            {
                return false;
            }
            _lastClick = Time.time;
            return true;
        }
    }
}

Basically, every time you ask it it you can click, it checks if a set amount of time (default 0.1 second) has passed since the last click. It’s usage is pretty simple: just make a behaviour that implements IInputClickHandler (from the Mixed Reality Toolkit) as usual, define a DoubleClickPreventer member, create it in Start like this

_doubleClickPreventer = new DoubleClickPreventer(0.5f);

and then in your OnInputClicked implementation use something like this:

if (_doubleClickPreventer.CanClick())
{
  // do stuff
}

and this will prevent a second click happening more than once every half second.

I made a little demo project, in which one cube has a GuardedClicker behaviour, that implements the DoubleClickPreventer, and the other a SimpleClickPreventer, that just registers every click.

image

If you click like a maniac for about a second or two on both cubes, you will clearly see a different result.

Note: the InputClickedEventData that you get in OnInputClicked.IInputClickHandler contains a “TapCount” property, but I have found that’s usually just 1, and however that does not stop the ‘stuttery double tap’ we are trying to prevent here. Also, this solution allows for fast clicks on separate objects, but not fast clicks on the same object.

The demo project (although it’s very little) can be downloaded here.

21 May 2018

Developing in Unity for Windows Mixed Reality without having to unplug your device all the time

A very simple but potentially quite a big time saving tip this time.

Typically, when you are developing for Windows Mixed Reality, you spend a lot of time in the Unity editor getting things just right. Unity and Mixed Reality integration is awesome - you can just hit play and your scene will show directly in your head set.

But sometimes, that is just not what you want. If you are fiddling with a tiny bit of interaction or animation code (and we all knows that can take a lot of time in Unity) you often just want to hit play, observe the results in the Game window, maybe move a bit around with the WASD keys or using an Xbox Controller. In that workflow, the necessity of putting on a  Mixed Reality device - and taking it off again - for every little iteration can be a cumbersome process.

There are two solutions for this: first, unplug your device if you don't need it. Duh. But if you use big desktop development box or this means reaching out to the back of the device. For laptops and desktop boxes both, you will need to fiddle with plugs, which in time might wear out or damage the plugs and/or the plug sockets of your PC. I am unfortunately speaking from experience here.

So what to use? Good ol'e device manager. Simply type "Device manager" in your start menu

image

You will find a node "Mixed Reality Devices". Find yours (I have a Samsung Odyssey indeed). Simply right-click

image

Hit "Disable device", click "Yes" on the rather ominous following warning, and your headset is now an expensive paperweight, no longer paying attention to what Unity does. You can now use Unity Play mode the 'old' way.

If you are done finicking in Unity, you can simply enable the device again using the Device Manager, and your awesome headset wakes up again.

14 May 2018

Fixing the "...Unity\Tools\AssemblyConverter.exe exited with code 1" error when you are building your Mixed Reality app

It's not easy being green - I mean, a Mixed Reality developer

This is one that has annoyed me for quite some time. When developing your Mixed Reality app, I usually go like this:

  • Change something in Unity
  • Build your Mixed Reality app from Unity
  • Open Visual Studio
  • Build your app and run in your HoloLens or Immersive headset
  • Be not entirely satisfied with the result
  • Change something more in Unity
  • Build your Mixed Reality app again

And then something like this happens:

image

An extremely unhelpful error message. If you copy the whole command in a command line and run the command yourself, you get a little more info

System.Exception: Unclean directory. Some assemblies are already converted, others are not.
    at Unity.SanityCheckStep.Execute()
    at Unity.Step.Execute(OperationContext operationContext, IStepContext previousStepContext)
    at Unity.Operation.Execute()
    at Unity.Program.Main(String[] args)

So here's a clue. Apparently some cruft stays behind preventing Unity from rebuilding the app the second time around. This is because Unity does not always overwrite all the files, presumably to to speed up the build process that second time. Only apparently they mess up sometimes.

UntitledSo then you go delete your generated app, but don't forget to retain some files you might want to keep (like your manifest file). You might add those to your repo - but then don't forget to revert after deleting, and oh yes, if you are testing on your local machine (and not your HoloLens or a different machine) you might find you can't even delete everything because it's locked. So you need to uninstall the app first. And this happens every second time you compile the app. And yes, this also happens when you use the Build Window.

Meh indeed

I never thought I would ever write this sentence, but here it goes:

PowerShell to the rescue

This first step you only need to do when you are testing on your development machine, and not on a HoloLens.

We  need to find out what the actual package name of your app is. The are two ways to do this. The simplest one is going over to your package.appxmanifest, double click it, select tab "packaging"

Untitled

Or you can just run a PowerShell Command like this:

Find name : Get-AppxPackage | Where-Object {$_ -like "*Walk*"}

Anyway, then you can make a script, call it "CleanApp.ps1" (or whatever you want to call it) and add the following commands:

Get-AppxPackage 99999LocalJoost.ThisIsMyApp | Remove-AppxPackage

$PSScriptRoot = Split-Path -Parent -Path $MyInvocation.MyCommand.Definition `
Get-ChildItem -Path ${PSScriptRoot}\App\ ` -include *.dll,*.pdb,*.winmd,*.pri,*.resw,Appx -Recurse | ` Remove-Item -Force -Recurse

This assumes your generated app is sitting in a directory "App" that is a sub directory of the directory that the actual script is sitting in. It typically place this in the root of my (Unity) project, while the App folder is a sub directory from that.

So your typical workflow becomes now:

  • Change something in Unity
  • Run this script
  • And then continue building the Mixed Reality app as you see fit (either from Unity to Visual Studio, or directly from the Build Window)

I deem you all capable of copying these lines of code from this blog post, so won't put any code online to go with this article.

05 May 2018

Running Mixed Reality apps on Windows 10 on ARM PCs–get ready for a surprise

Intro

I was planning to write a step-by-step procedure of the things you would need to do to get the Mixed Reality app I created in my previous post to work on a Windows 10 on ARM PC. After all, when I tried to do that on a Raspberry PI2 quite some time ago, there was some creative slashing necessary.

Life is what happens while you are busy making other plans

Turns that what I needed to do was exactly nothing. Well, I had to compile and deploy it for ARM. And that worked. Just like that, just like on a intel-based PC as I described in my previous post. When I deployed Walk the World to the Windows 10 on ARM PC some posts ago, I still had to remove some parts of the Mixed Reality Toolkit to make the ARM tools swallow the sources. Apparently, that’s no longer necessary.

And then I tested it. And I learned I had to make some changes to my code after all. I think Microsoft likes to hear that you can run code on Windows 10 on ARM PCs unchanged, but in this case I don’t think they will mind me saying this I actually needed to make some changes because it was running too bloody fast on a Windows 10 on ARM PC. Yeah, you read that right. The code I wrote for controlling the app via an Xbox One Controller replied so fast it was actually nearly impossible to control the view point, especially when rotating. Even when I compiled it for x86 and CHPE had to do the translation, it still ran too fast for reasonable control.

It actually ran faster than on my i7 Surface Pro 4. That was one serious WTF, I can tell you that.

One trigger, two triggers

You might remember that in the previous post I used the right trigger to make moving and rotating go faster. Well we sure don’t need to go faster, so I adapted the code to calculate the speed up factor:

var speed = 1.0f + TriggerAccerationFactor * eventData.XboxRightTriggerAxis;

To use the right trigger to slow down the speed.

var speed = (1.0f + TriggerAccerationFactor * eventData.XboxRightTriggerAxis) - 
            (eventData.XboxLeftTriggerAxis * 0.9f);

And that works reasonably well.

Now I made a setup quite comparable to my previous post on Windows 10 on ARM, only now the x86/ARM versions are not only compared with each other, but also with an x64 version running on my Surface Pro 4.IMG_6845_2

The Surface Pro 4 for is running on his own screen and is connected to the right Xbox Controller and the gray ArcMouse, the Windows 10 on ARM PC, once again missing from this picture, is connected to the black ArcMouse, and Dell monitor and the left Xbox Controller via the Continuum dock that you can see just in front of the MVP thermos.

So here’s a little video of the three versions:

You can clearly see the the Windows on ARM10 PC is quite a bit faster than the Surface Pro 4 and that even the x86 CHPE-fied version is faster, so that rotating indeed needs the left trigger to slow it down, to get some resemblance of control. At the end, you can actually seen them all three together

IMG_6852_3

The difference between the x86 and the ARM version is mainly in startup time here and a wee bit of general performance (although you mainly notice that when you actually operate the app – if you just watch it’s less obvious). Last time I wrote about Windows 10 on ARM I already concluded that CHPE does an amazing job as far as graphics performance goes, and it shows here again.

[image%5B22%5D]Interesting detail – the Windows 10 on ARM PC does not show this popup a the end, while the Surface Pro 4 does. Now this may be because Windows x64 actually has the optional “Windows Mixed Reality” component (although this particular hardware doesn’t support that), and Windows 10 on ARM does not have that particular component. Also, the latter still runs the Fall Creators Update, while the Surface Pro 4 runs the April 2018 update. Both may be a factor. I have no way to test this now.

Two versions of the same app?

You might have noticed this before - I sometimes run two versions of the same app together on one PC. That's normally not possible - if you deploy one version it gets overwritten by the other, even when you change target architecture in Visual Studio. To get two version of the same app to run of one computer, you will need to fiddle somewhat in the Package.appmanifest. Open it as XML file (not via the beautiful GUI editor provided by Visual Studio). Change the Name in Identity (3rd line in the file)

<?xml version="1.0" encoding="utf-8"?>
<Package xmlns:....
   <Identity Name="XBoxControllerDemo" Publisher="CN=DefaultCompany" Version="1.0.0.0" />

and change XBoxControllerDemo for instance to XBoxControllerDemoARM

Then look a bit lower for the VisualElements tag

<uap:VisualElements DisplayName="XBoxControllerDemo"

And change that to for instance "XBoxController ARM Version" - to make sure the app also have separate icon labels.

Do not ever do this on production apps but if you want to you your own kind of crazy A-B testing like me it can be useful.

Conclusion

This article is quite a bit shorter than I anticipated, but that it’s because Mixed Reality apps seem to run amazingly well on Windows 10 on ARM PCs with very little work. This platform is a serious candidate for Unity generated UWP apps.

I am now seriously considering rebuilding my Mixed Reality apps with this new MRTK and the newest applicable version of Unity, and including an ARM package in the store. Why not. It runs fine. Let's see if users like it.

No (new) project this time. You can find the project with the updated XBoxControllerAppControl.cs (still) here.

02 May 2018

Running your Mixed Reality app on an ‘ordinary’ PC–using an Xbox One Controller

Intro

Let’s face it – although Windows Mixed Reality has a steady uptick (at least I think I can draw that conclusion from the increasing download numbers of my two Mixed Reality apps in the Windows Store) – not everyone has a Mixed Reality headset, or even has a PC capable of supporting that. Time will take care of that soon enough. In the mean time, as a Mixed Reality developer, you might want to show all 700 million Windows 10 users a glimpse of your app, in stead of ‘only’ the HoloLens and Mixed Reality headset owners out there. Even in a reduced state, it gives you eyeballs, and maybe entice them to get themselves a headset after all. It’s not like they are expensive these days.

This sounds familiar?

Well it should. This is far from original. I have been down this road before, describing how to run a HoloLens app on a Raspberry PI2. That’s the U in UWP for you. Only now we are going to run on a full PC – in my case, a Surface Pro 4. That’s a sufficiently high end device for a nice experience, but it predates the Windows Mixed Reality era by almost two years and does not support it. But you can’t walk around without a headset, so we will need another means to change our view point.

Parts list

  • One reasonably nice performing PC not capable of supporting Mixed Reality – or at least with the Mixed Reality portal not installed
  • Unity 2017.2.1p2
  • The Mixed Reality Toolkit 
  • One XBox One controller

The first point is important – for if you have the portal installed, your PC will launch it like a good boy trying to do the logical thing - and you won’t see the effect I am trying to show you.

Setting up the project

I created a new project in Unity, copied in the latest Mixed Reality Toolkit, then clicked the three menu options under Mixed Reality Toolkit/Configure.

Then I added my standard empty game objects “Managers” (with nothing in it)  and “HologramCollection” with a cube and a sphere, to have something to see:

image

There is more to that two objects that meets the eye but we will get to that later.

Control the view point using an XBox Controller

There’s a simple class for that, in my ever growing HolotoolkitExtensions, that starts like this

using HoloToolkit.Unity.InputModule;
using UnityEngine;

namespace HoloToolkitExtensions.Utilities
{
    public class XBoxControllerAppControl : MonoBehaviour, IXboxControllerHandler
    {
        public float Rotatespeed = 0.6f;
        public float MoveSpeed = 0.05f;
        public float TriggerAccerationFactor = 2f;

        private Quaternion _initialRotation;
        private Vector3 _initialPosition;

        private readonly DoubleClickPreventer _doubleClickPreventer = 
                                                new DoubleClickPreventer();
        void Start()
        {
            _initialRotation = gameObject.transform.rotation;
            _initialPosition = gameObject.transform.position;
        }
    }
}

I tend to offer settings to the Unity editor as much as possible - to make it easy to reuse this class and adapt its behavior without code changes. Here I offer some speed settings. You can set the maximal rotation speed and the maximal speed the camera moves, and the ‘speed up factor’ that is applied to all values when the right trigger is pressed. Be advised these are all analog values between 0 and 1, so you can control the speed anyway by varying the amount of pressure you apply to the sticks, the D-pad. But sometimes you just wanna go fast, hence the trigger. Also notice how initial rotation and position are retained.

The main routine is of course OnXboxInputUpdate, as the IXboxControllerHandler mandates its presence.

public void OnXboxInputUpdate(XboxControllerEventData eventData)
{
    if (!UnityEngine.XR.XRDevice.isPresent)
    {
        var speed = 1.0f + TriggerAccerationFactor * eventData.XboxRightTriggerAxis;

        gameObject.transform.position += eventData.XboxLeftStickHorizontalAxis * 
                                         gameObject.transform.right * MoveSpeed * speed;
        gameObject.transform.position += eventData.XboxLeftStickVerticalAxis * 
                                         gameObject.transform.forward * MoveSpeed * speed;

        gameObject.transform.RotateAround(gameObject.transform.position, 
            gameObject.transform.up, 
            eventData.XboxRightStickHorizontalAxis * Rotatespeed * speed);
        gameObject.transform.RotateAround(gameObject.transform.position, 
            gameObject.transform.right, 
            -eventData.XboxRightStickVerticalAxis * Rotatespeed * speed);

        gameObject.transform.RotateAround(gameObject.transform.position, 
            gameObject.transform.forward, 
            eventData.XboxDpadHorizontalAxis * Rotatespeed * speed);

        var delta = Mathf.Sign(eventData.XboxDpadVerticalAxis) * 
                    gameObject.transform.up * MoveSpeed * speed;
        if (Mathf.Abs(eventData.XboxDpadVerticalAxis) > 0.0001f)
        {
            gameObject.transform.position += delta;
        }

        if (eventData.XboxB_Pressed)
        {
            if (!_doubleClickPreventer.CanClick()) return;
            gameObject.transform.position = _initialPosition;
            gameObject.transform.rotation = _initialRotation;
        }

        HandleCustomAction(eventData);
    }
}

Let’s unpack that a little.

Important is the if (!UnityEngine.XR.XRDevice.isPresent). We only want this behaviour to do it’s work when there is no headset present whatsoever – no Mixed Reality head set, no HoloLens.

  • First we calculate a possible ‘speed up factor’ to be applied when the trigger is used. If it is not, it’s simply 1 and has no effect to the actual movement or rotation.
  • The left stick is used for movement in the ‘horizontal’ plane – forward, backward, left, right. Be aware the axes are relative. So if you are rotated 45 degrees left and you move left, you will move 45 degrees left. It’s actually logical – your frame of reference is always yourself, not some random rotation that happened to be in place when you got somewhere.
  • The right stick is used for rotation around your top and horizontal axis (left to right). Moving it to right will make you spin to the right (I negate the actual value coming from the stick as you can only rotate a game object around it’s left axis), pushing it forward will make you look at the floor.
  • That leaves moving up and down, and rotating left and right. The D-pad fills the voids: pushing it left or right will make you rotate sideways (like you are falling to the left or right), pushing it up or down will make your viewpoint move up or down.

This is exactly the way it works when you use an Xbox Controller to steer the Unity editor in play mode. The D-pad feels a bit counter-intuitive to me, but when you try to move in three dimensions using sticks that move both in only two dimensions, you will need something extra, and the D-pad is the only thing left. It feels odd to me, but it works.

Then finally the B button – when you press that, you get back to your initial position. This is very useful for if you have messed around a bit too much and completely lost track of where you are. And that is mostly all of it.

A tiny bit of SOLID

protected virtual void HandleCustomAction(XboxControllerEventData eventData)
{
}

Hardly worth mentioning, but should you want to add your own logic handling controller buttons or triggers, you can make a child class of this XBoxControllerAppControl  and override this method. It’s a hook that makes it open for extension, but keeps it own logic intact. That’s better than making OnXboxInputUpdate virtual, because that enables you to interfere with the existing logic by not calling the base OnXboxInputUpdate. It’s the O of SOLID. image

How to use it

Simply drag it to the the MixedRealityCameraParent, change the settings to your liking and your are done. I think I took some reasonable default settings.

But wait, there’s more!

I have found the Xbox Controller buttons tend to stutter – that is, they sometimes fire repeatedly and rapid fire events can give a bit of a mess.

So I created this little helper DoubleClickPreventer that is not exactly rocket science, but very useful

using UnityEngine;

namespace HoloToolkitExtensions.Utilities
{
    public class DoubleClickPreventer
    {
        private readonly float _clickTimeOut;

        private float _lastClick;

        public DoubleClickPreventer(float clickTimeOut = 0.1f)
        {
            _clickTimeOut = clickTimeOut;
        }

        public bool CanClick()
        {
            if (!(Time.time - _lastClick > _clickTimeOut))
            {
                return false;
            }
            _lastClick = Time.time;
            return true;
        }
    }
}

It’s rather simple: whenever the method CanClick is called, a time is set. If the method is called twice within 0.1 seconds it returns false, otherwise it returns true. It’s actually used twice within this sample: it’s also on on the little helper class “SelectorDemo” that makes the sphere and the cube go “plonk” and flash blue when you click them using the Xbox “A” button. I won’t go into that – you can find it in the demo project, and it’s inner workings are left as exercise to the reader.

And it looks like…

There are a few things you might notice. First of all, I apparently am able to select something, but I never coded for it. That’s courtesy of the Mixed Reality Toolkit – your Xbox Controller’s “A” button is acting the same as saying “Select” in a Mixed Reality app while you are gazing at something, air tapping while using a HoloLens, or pointing your Mixed Reality controller to an object and pressing the trigger.

Also, you might notice this at the end of the video:

image

A clear sign Windows is not really content with this. It figures – because if nothing prevents you from downloading an app that simply does not work on your machine it might disgruntle users. But still – the app launches and seems to work.

Some other things to notice and take into consideration

  • Use the right Unity version: 2017.2.1p2. That’s the one that goes with this release of the Mixed Reality Toolkit. Using newer versions of Unity or the toolkit (like the development branch) I got results varying from the app not wanting to compile, crashing or simply not starting. I also got just this “Can’t open app” dialog and nothing else
  • You can also see (very small) “Development build” in the lower right corner. There’s a check box in Unity that everyone tells you to use, and then that text will go away. The trouble is, that does not work. What will make it go away, is building the app with the Master configuration. That and only that. For Mixed Reality apps, this check box apparently only is there for show. At least as far as this text is concerned, and as far as I can see ;).

buildmaster

  • And finally, when making these apps run on an ordinary PC, you might want to rethink the UI a bit at places. Floating menu’s, which are very cool in real Mixed Reality environments, can be really hard to use on a flat screen, for instance. Also, placing things on top of the ‘floor’ might be a bit of a challenge without a floor – even a virtual one.

Concluding words

I am not sure if this will continue working going forward with the MRTK and Unity, how useful this will be in the real word, or if that the Mixed Reality team even appreciates this approach. I am simply showing you what’s possible and a possible way to tackle this. Your mileage may vary, very much in fact. Have fun!

Once again – demo project here