Collision Frustrations

*^{warning: no answer}*

So you are making a ID3DXMesh for your mesh, to do CD?
I''m loading MD2''s and I''m lookign for a way to do collision detection too, but is this the right way?

.lick

Wow.
I''m trying to use MD2 models with DirectX9.
And my plan was to use simple bounding spheres.
I didnt know you could perform collision detection at mesh-level!

If you figure this out, please say so...as I and probably a few others will be very interested in knowing how to do just that!

okay, of course I have my up, look, and right vectors
and my position.

All you need to do is multiply all these by the model matrix?

That seems like a lot of wasted time! Is their an easier/better way?

And for all others:

I do use spheres for a lot of collision tests, but to get more accurate CD, if I cross the bounding sphere, then cast a ray to see if it hits a poly.

I got collision detection working fine for my landscape, but it is these transformed models that are posing a problem.

I am NOT using id3dx mesh just to reiterate.

quote:

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Original post by RhoneRanger
I dont use X files, so telling me to use D3DX in this matter will not do.

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You can use D3DX without using X files by doing this:

D3DXCreateMeshFVF();

Mesh->LockVertexBuffer();
Mesh->LockIndexBuffer();

... // Fill in the vertex and index buffers

Mesh->UnlockVertexBuffer();
Mesh->UnlockIndexBuffer
 

then if you want to transform your mesh''s coordinates to world
coordinates you can try D3DXVec3TransformCoord

I hope this helps

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KaM1KaZ3

The whole point I am making is that I want to do collision on models in world space. I have very good and fast functions for collisions, but all I need to do is to fill the copy of vertices of the object I have in system memory with the position of the Transformed vertices. That''s all.

I don''t want to lock and unlock vertex/index buffers every frame, when all I have to do is this:

If you are in same area as model:

perform sphere/sphere test.

if you intersect spheres:
perform ray-triangle test on mesh.

Here are a few suggestions:

You do not want to try and retrive the transformed mesh from DX, as this will hinder performance.

It is cheaper and easier to transform the ray/sphere or whatever into the models local space because:

1) tranforming the start/end point ( and possibly direction ) vectors is far cheaper than rotating every vert in a mesh to world space.

2) if you have the mesh instanced twice in the world you would have to store 2 transformed meshes, or do it several times a frame.

3) You want to do collision on the CPU, not the GPU as this will cause stalls -> lower performance.

There have been many threads discussing similar issues, it might be a good idea to look into those too.

Other people have good advice on this topic (See threads by Simon O''Conner amongst others )

hope this is of some help.

Mark, thanks for the reply!

So all I need to do is transform my ray into model space. I will look into Simons posts, and I appreciate the help!