How do I find hash value of a 3D vector ?

Question

I am trying to perform broad-phase collision detection with a fixed-grid size approach. Thus, for each entity's position: (x,y,z) (each of type float), I need to find which cell does the entity lie in. I then intend to store all the cells in a hash-table and then iterate through to report (if any) collisions.

So, here is what I am doing: Grid-cell's position: (int type) (Gx, Gy, Gz) => (x / M, y / M, z / M) where M is the size of the grid.

Once, I have a cell, I'd like to add it to a hash-table with its key being a unique hash based on (Gx, Gy, Gz) and the value being the cell itself. Now, I cannot think of a good hash function and I need some help with that.

Can someone please suggest me a good hash function?

Thanks

Answer 1

If someone is still interested in this, I figured out a solution that works over here:

http://www.gamedev.net/community/forums/topic.asp?topic_id=567378

Answer 2

The grid approach is going to have problems near the boundaries of the grid boxes. Why not use BSP trees instead?

Answer 3

My preferred hashing function for this kind of vector is to rotate the bits of each component by a different constant and XOR them together.

It's very fast, and the bit rotations are helpful to reduce collisions and ensure as much of the key space as possible is used.