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I am a lil bit confused about definition of D3DXVECTOR3 in directX 9. As far as I know a vector is a quantity, defined by both magnitude and direction.
In directX 9 if you define a D3DXVECTOR3 type variable, your variable has 3 parameter which are x, y, z. These x, y, z is a point in space.
So how come a point is defined as vector?
A point is not defined as a vector.
If B=(i, j, k) is an ordered basis for 3D vectors, then for any 3D vector v, there exist unique scalars a1, a2, a3 such that:
v = a1*i + a2*j + a3*k
So given a basis, the coordinates (a1, a2, a3) are enough to uniquely identify the vector v, and we say that [v]_B is the coordinate representation of the vector v.
In computation, we always work with coordinate vectors which are relative to some working basis.
