Highlight Spatial Mesh polygon where collision occurs

mdouk

Hello everyone,

For my application I would like to identify where collisions between my holograms and the Spatial Mesh occur. Is there a way to "paint" (e.g. with red) the exact Spatial Mesh polygon (where the collision occured) that caused the collision?

Thanks in advance,
Michael

askrips

I think the Holographic Academy can help you. The course Holograms 101 demonstrates HoloLens features including spatial mapping https://developer.microsoft.com/en-us/windows/holographic/holograms_101

mdouk

Thanks askrips! However, I have gone through 101 but I still cannot understand how to identify where the collision was made and highlight the Spatial Mesh polygon. Any other ideas?

james_ashley

@mdouk,

You should be able to get a reference to the mesh you're hologram is colliding with using the OnTriggerEnter method. Here are the basics on using it, though you probably will want to find a video explaining how to use it for collision detection if you aren't already familiar, since there are a few gotchas.

I believe OnTriggerEnter will pass you the collider, from which you can get the spatial mapping Surface object. From that, in turn, you can grab the mesh renderer and activate it like so:

    public void OnTriggerEnter(Collider other)
    {
        GameObject surface = other.gameObject;
        Renderer renderer = surface.GetComponent<MeshRenderer>();
        renderer.enabled = true;
    }

At least I think this will work. I'd have to get to my dev computer to test it out.

civitas

@james_ashley said:
@mdouk,

You should be able to get a reference to the mesh you're hologram is colliding with using the OnTriggerEnter method. Here are the basics on using it, though you probably will want to find a video explaining how to use it for collision detection if you aren't already familiar, since there are a few gotchas.

I believe OnTriggerEnter will pass you the collider, from which you can get the spatial mapping Surface object. From that, in turn, you can grab the mesh renderer and activate it like so:

    public void OnTriggerEnter(Collider other)
    {
        GameObject surface = other.gameObject;
        Renderer renderer = surface.GetComponent<MeshRenderer>();
        renderer.enabled = true;
    }

At least I think this will work. I'd have to get to my dev computer to test it out.

May I ask a bit more: how to achieve something like RoboRaid? Render some spatial mesh from a certain point and radius?

james_ashley

@civitas,

Hmmm. I have an idea on that. Let me work on a demo for a day and get back to you.

mdouk

@civitas said:

@james_ashley said:
@mdouk,

You should be able to get a reference to the mesh you're hologram is colliding with using the OnTriggerEnter method. Here are the basics on using it, though you probably will want to find a video explaining how to use it for collision detection if you aren't already familiar, since there are a few gotchas.

I believe OnTriggerEnter will pass you the collider, from which you can get the spatial mapping Surface object. From that, in turn, you can grab the mesh renderer and activate it like so:

    public void OnTriggerEnter(Collider other)
    {
        GameObject surface = other.gameObject;
        Renderer renderer = surface.GetComponent<MeshRenderer>();
        renderer.enabled = true;
    }

At least I think this will work. I'd have to get to my dev computer to test it out.

May I ask a bit more: how to achieve something like RoboRaid? Render some spatial mesh from a certain point and radius?

I put this in an existing script that I attach to my GameObject and added the following code for the color change:
transform.GetComponent<MeshRenderer>().material.color = Color.red;

But still when a collider happens I dont see the Spatial Mesh polygon change color...What more should I do?

mdouk

@james_ashley

After a lot of tries, I cannot get this to work.
The component MeshRenderer fetches the entire SpatialMesh and not the polygon where the collisions occured. Even in that case, the SpatialMesh does not change its colour upon collision. Although if I insert a kinematic game object (KGO) then its colour is being changed when my movable game object (MGO).

My script follows. Pls note that it also changes the colour of my MGO which works just fine:

`public class ColourChange : MonoBehaviour {

public float colourChangeDelay = 10.0f;
float currentDelay = 0.0f;
bool colourChangeCollision = false;
private Color MGOBlue = new Color (0f, 159f, 255f, 255f);
private Color meshPolygon = new Color (255f, 0f, 0f, 255f);

void OnTriggerEnter(Collider other) 
{
    colourChangeCollision = true;
    currentDelay = Time.time + colourChangeDelay;

    //change the colour of the colliding mesh of the Spatial Mesh into Materials/meshPolygon
    GameObject surface = other.gameObject;
    MeshRenderer renderer = surface.GetComponent<MeshRenderer>();
    renderer.enabled = true;
    surface.transform.GetComponent<MeshRenderer>().material.color = meshPolygon;
}

void checkColourChange()
{        
    if(colourChangeCollision)
    {
        transform.GetComponent<Renderer>().material.color = Color.yellow;
        if(Time.time > currentDelay)
        {
            // change the colour to Materials/MGOBlue
            transform.GetComponent<Renderer>().material.color = MGOBlue;
            colourChangeCollision = false;
        }
    }
}

void Update()
{
    checkColourChange();
}

}`

Moreover, I have found the following code, which may eventually be helpful:
void OnCollisionEnter(Collision collision) { foreach (ContactPoint contact in collision.contacts) { Debug.DrawRay(contact.point, contact.normal, Color.red); }

Any further ideas?
Thanks in advance
Micheal

mdouk

up?

jbienzms

In addition to what's already been shared, I recommend checking out Holograms 240. Just download the zip and open the Completed folder in Unity. Then, check out the CustomSpatialMapping prefab in the Holograms subfolder. It only shows the wireframe in specific areas where objects collide with it and it even generates polys that "fracture" away from the surface when an object collides. It's a very neat effect.

trzy

Not sure how Holograms 240 does it -- it may be just what you need -- but I've played around a bit with Microsoft's RemoveVertices component and discovered that the implementation is not quite correct.

I implemented oriented bounding box/mesh intersection testing to determine which triangles a box collider intersects. Basically, you would want to do an intersection test of your object (hopefully a simple shape like a box, or even just a ray) against meshes, find the affected polygons, and then create a new GameObject with a mesh containing only those polygons.

My intersection testing code is available on my Github under Assets/Scripts/OBBMeshIntersection.cs: https://github.com/trzy/hololens/tree/master/Experiments-Unity

mdouk

@jbienzms @trzy
Thanks for the further suggestions. I think the way to go would be a combination of both Tutorial 240 Spatial Mapping Deformation and bounding box/mesh intersection. Once I check it out I will let you know!