Implementing a high-resolution collision detection

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Implementing a high-resolution collision detection

(13 posts) (6 voices)

Started 8 months ago by Tenorm
Latest reply from Tenorm

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Tenorm
Member
Hi,

I tried to implement a high-resolution collision detection and found this two very useful commands:
```
CC3PlaneFromPoints(<#CC3Vector p1#>, <#CC3Vector p2#>, <#CC3Vector p3#>);
CC3RayIntersectionWithPlane(<#CC3Ray ray#>, <#CC3Plane plane#>);
```
So I want to check for collision by computing the distance to all of the faces of an object. But I don't know how to access them... I found this:
CC3VertexLocations* vertices = ((CC3VertexArrayMeshModel*)node.meshModel).vertexLocations;
but I don't know which three vertices of this pool make a face. So my basic question is how to make a loop that checks all the FACES of an object.

Thank you!

By the way: How to use CC3Ray?
Posted 8 months ago #
catdsnny
Member

Definitely need a way to get to the poly list to implement any kind of collision detection.

Posted 4 months ago #
Bill Hollings
Moderator

@catdsnny

Code for accessing faces will be included in the next release, which will be out by the end of January.

...Bill

Posted 4 months ago #
Gray Olson
Member

The only current way to do this is to use a physics engine, which also isn't directly supported, but manageable with some research, also my wrapper may help. We (by we I mean Bill and I was going to help then life got hectic) want to include physics support but we want it to be interchangeable so you can use whichever engine you'd like as long as someone writes a "plugin" for it that would give cocos some info that it can use to sync itself with the physics engine as well as command it through objective c commands that feel like cocos.

Gray

Posted 4 months ago #
Tenorm
Member

It IS possible. I did it! When I have some spare time maybe I will post the Ray-VS-Object-Collision code in a better condition than I use it ;)

Posted 4 months ago #
Gray Olson
Member

Oh? Cool! Love to see the code :)

Posted 4 months ago #

Tenorm
Member

-(CC3Vector4)intersectMeshNode:(CC3MeshNode*)node:(CC3Vector)position:(CC3Vector)direction
{
    bool success;

    CC3VertexLocations* vertices = ((CC3VertexArrayMeshModel*)node.meshModel).vertexLocations;

    for(int i=0; i<vertices.elementCount; i=i+3)
    {
        CC3Vector pos1 = (CC3Vector)([node vertexLocationAt:i]);
        pos1 = CC3VectorScale(pos1,node.scale);
        CC3Vector pos2 = (CC3Vector)([node vertexLocationAt:i+1]);
        pos2 = CC3VectorScale(pos2,node.scale);
        CC3Vector pos3 = (CC3Vector)([node vertexLocationAt:i+2]);
        pos3 = CC3VectorScale(pos3,node.scale);

        CC3Vector4 ret = RayIntersectionTriangle(position,direction,pos1,pos2,pos3,&success);

        if(success)return ret;
    }

    return CC3Vector4Make(0,0,0,0);
}

And the RayIntersectionTriangle-Function:

CC3Vector4 RayIntersectionTriangle(CC3Vector p,
                                   CC3Vector d,
                                   CC3Vector v0,
                                   CC3Vector v1,
                                   CC3Vector v2,
                                   bool* success)
{
    float a,f,u,v,t;
    CC3Vector e1 = CC3VectorDifference(v1,v0);
    CC3Vector e2 = CC3VectorDifference(v2,v0);

    CC3Vector h = CC3VectorCross(d,e2);
    a = CC3VectorDot(e1,h);

    if (a > -0.00001 && a < 0.00001)
    {
        *success = NO;
        return CC3Vector4Make(0,0,0,0);
    }

    f = 1/a;
    CC3Vector s = CC3VectorDifference(p,v0);
    u = f * (CC3VectorDot(s,h));

    if (u < 0.0 || u > 1.0)
    {
        *success = NO;
        return CC3Vector4Make(0,0,0,0);
    }

    CC3Vector q = CC3VectorCross(s,e1);
    v = f * (CC3VectorDot(d,q));

    if (v < 0.0 || u + v > 1.0)
    {
        *success = NO;
        return CC3Vector4Make(0,0,0,0);
    }

    t = f * (CC3VectorDot(e2,q));

    *success = YES;
    return CC3Vector4Make(t,u,v,0);
}

Have fun!

-----

Edit: It is important to use a non-sorted triangle-list in the COLLADA->POD-Exporter:

Primitive Type = "Triangle list" (disable "Indexed")
Triangle Sort = "None" (disable "Sort vertices")

That's why:

1. Face = Vertices{0,1,2}
2. Face = Vertices{3,4,5}
3. Face = Vertices{6,7,8}
...

Posted 4 months ago #

Tenorm
Member

Sry: There was an failure, this is the correct way:

-(float)intersectMeshNode:(CC3MeshNode*)node:(CC3Vector)position:(CC3Vector)direction
{
    bool success;

    CC3VertexLocations* vertices = ((CC3VertexArrayMeshModel*)node.meshModel).vertexLocations;

    for(int i=0; i<vertices.elementCount; i=i+3)
    {
        CC3Vector pos1 = (CC3Vector)([node vertexLocationAt:i]);
        pos1 = CC3VectorScale(pos1,node.scale);
        CC3Vector pos2 = (CC3Vector)([node vertexLocationAt:i+1]);
        pos2 = CC3VectorScale(pos2,node.scale);
        CC3Vector pos3 = (CC3Vector)([node vertexLocationAt:i+2]);
        pos3 = CC3VectorScale(pos3,node.scale);

        float ret = RayIntersectionTriangle(position,direction,pos1,pos2,pos3,&success);

        return ret;
    }

    return 0;
}

And the RayIntersectionTriangle-Function:

float RayIntersectionTriangle(CC3Vector p,
                                   CC3Vector d,
                                   CC3Vector v0,
                                   CC3Vector v1,
                                   CC3Vector v2,
                                   bool* success)
{
    float a,f,u,v,t;
    CC3Vector e1 = CC3VectorDifference(v1,v0);
    CC3Vector e2 = CC3VectorDifference(v2,v0);

    CC3Vector h = CC3VectorCross(d,e2);
    a = CC3VectorDot(e1,h);

    if (a > -0.00001 && a < 0.00001)
    {
        *success = NO;
        return 0;
    }

    f = 1/a;
    CC3Vector s = CC3VectorDifference(p,v0);
    u = f * (CC3VectorDot(s,h));

    if (u < 0.0 || u > 1.0)
    {
        *success = NO;
        return 0;
    }

    CC3Vector q = CC3VectorCross(s,e1);
    v = f * (CC3VectorDot(d,q));

    if (v < 0.0 || u + v > 1.0)
    {
        *success = NO;
        return 0;
    }

    t = f * (CC3VectorDot(e2,q));

    *success = YES;
    return t;
}

Have fun!

Notice: position and direction of the ray are relative to the meshnode's, not to the world's coordinate system. But you could apply the meshnode's position and rotation to the Vectors pos1, pos2 and pos3.

Posted 4 months ago #

duncan
Member

Maybe I'm not getting this right. but in your correction you have

float ret = RayIntersectionTriangle(position,direction,pos1,pos2,pos3,&success);

return ret;

Shouldn't it be

if(success)return ret;

?

Otherwise it would exit on the first iteration.

Posted 3 months ago #
Tenorm
Member

Of course you're right!

Posted 1 month ago #
Bill Hollings
Moderator

@Tenorm

I thought I'd let you know that the release of cocos3d coming out this week includes basic collision detection and ray-intersection-tracing.

The basic collision detection is not at the per-face level, but this release also includes easy access to the individual faces of a model, to make it easier to do the kinds of things you are trying to do.

...Bill

Posted 1 month ago #
HHG
Member

@Bill... look forward to the update!

Thx,
Thomas

Posted 1 month ago #
Tenorm
Member

@Bill Thank you!

Posted 3 weeks ago #

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