On 6/14/06, Janek Kozicki <janek_listy@wp.pl> wrote:
Another question - would quaternions be something like vector<4,double> ? For me it looks like a good idea. Template specialization can offer category A operations that are specific to quaternions, when someone works with unitless vector<4>.
It would be just like template specialization will provide cross product for vector<3>, which is specific only for vector<3>.
Besides quaternions are also known to be used together with matrix<4,4,double>.
I don't think this is the correct thing to do. There are uses of vector<4> where quaternion operations don't make sense, but classic vector operations do. In graphics programming vector<4>s are sometimes used as the color component, with data encoded into each field to be used by a hardware shader. There are often times where the 'w' component is used to signal that the vertex is at infinity, but should otherwise still be treated as a classic vector<3>. For lights, the 'w' component is used to signal the type of light, directional or point (omni-directional). That type specifies how the x,y,z components should be interpreted. If the light is directional, then the x,y,z is a direction vector. If the type is a point light, the x,y,z components are a position in space. I agree about the only allowing certain operations using template specialization for the vector/quaternion classes, but I disagree that quaternion can simply be vector<4> with the provided quaternion specializations. I think it should be a separate class following the same principles. I currently use enable_if and is_same from boost to determine what functions should be exposed. There are convenience functions like: as_array() to be used like glVertex3fv(my_vec.as_array()); that only make sense if the vector contained all of the same type. Otherwise, in cases like vec3<float, short, float>, as_array() would be disabled. I suspect that we could do the same for the rest of the operations (dot_product, cross_product, etc). --Michael Fawcett