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Juliean

Collision Detection with D3DXIntersect()

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Hi,

I just tried out collision detection with D3DXIntersect(), and although it basically seems to be working as I get some results, I wondered how to work with the values I got from D3DXInteresect()? Currently, I'm doing it that way:

BOOL Collision;
DWORD FaceIndex;
LPD3DXPMESH Mesh = ObjectManager.GetObject(0)->GetModel()->GetMesh();
float u;
float v;
float d;
D3DXIntersect(Mesh, &D3DXVECTOR3(0, 0, 0), &D3DXVECTOR3(0, -1, 0), &Collision, &FaceIndex, &u, &v, &d, NULL, NULL);

DWORD* Indices = NULL;

Mesh->LockIndexBuffer(D3DLOCK_NOOVERWRITE | D3DLOCK_READONLY, (void**)&Indices);

FaceIndex -= FaceIndex%3;

int v1, v2, v3;

v1 = Indices[FaceIndex];
v2 = Indices[FaceIndex+1];
v3 = Indices[FaceIndex+2];

Mesh->UnlockIndexBuffer();

MeshVertices* Vertices = NULL;

D3DXVECTOR3 p1, p2, p3, p;

Mesh->LockVertexBuffer(D3DLOCK_NOOVERWRITE | D3DLOCK_READONLY, (void**)&Vertices);

p1 = Vertices[v1].Position;
p2 = Vertices[v2].Position;
p3 = Vertices[v3].Position;

Mesh->UnlockVertexBuffer();

p = p1 + u*(p2 - p1) + v*(p3 - p1);


So, just to make sure everything works OK I'm casing a ray from the origin down the y-axis. I should get some 0/y/0-point, however what I get is some random point. So I quess I'm trying to access the wrong vertices. What I figured was that: The index of the nearest vertex I get from D3DXIntersect minus its modulo with 3 should give me the 3 vertices of the face the ray intersected with. Then I'd access that vertices, and access it's positions. Using the formula given on the msdn site I can calculate the actual intersection point.

So, does anyone see what I did wrong? I was using a non-transformed mesh, and my ray can't really be wrong, so I guess that my understanding of how to access index/vertex data from the returned values of D3DXIntersect() is wrong. Can somebody tell me how this is done properly? Thanks in advance!

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