Using a Matrix to transform vectors

[Acki]

hi,
I have 8 vectors that build a bounding box...
and I have the transformation matrix of a node...

but how do I use the matrix to translate and rotate the vectors ???

sorry for my ignorance...

[CuteAlien]

Check CMatrix4<T>::transformVect in matrix4.h which does just that.
Or if you want more info check https://en.wikipedia.org/wiki/Matrix_multiplication (a vector can be thought of as a 1x3 or 3x1 matrix).
So it's a matrix-multiplication of the inner 3x3 matrix with the vector - and the translation part (elements 12-14 in Irrlicht) is simply added. Forget about 4th row for now it's usually 0.

And be careful that the inner 3x3 not only rotates but can also scale.

Or if you want to visualize it - the inner 3x3 matrix is basically describing your 3 axes of your coordinate system. And vectors are a multiplication with those axes. X*first axis+ Y*second axis + Z*third axis (which ends up being x = x*axis1.x+y*axis2.x+z*axis3.x as each axis can have an x part, same for y and z) We usually don't think about it for the simple case (the identity matrix) as all the multlications by 0 fall away and so result is just (x,y,z) again but the usual Cartesian coordinates are also a multiplication by the axes. If the 3 axis go in another direction and you do the same calculation then it moves your coordinate in those directions. So once you got a matrix things are pretty simple. Creating the matrix can be a bit more tricky (tends to involve the sin/cos stuff which you learned in school to use for rotations to rotate the original axes toward their new position).