Matrix rotation wrong orientation LibGDX

Question

I'm having a problem with matrix rotation in libgdx. I rotate it using the method matrix.rotate(Vector3 axis, float angle) but the rotation happens in the model orientation and I need it happens in the world orientation.

For example:

on create() method:

matrix.rotate(new Vector3(0,0,1), 45);

That is ok, but after:

on render() method:

matrix.rotate(new Vector3(0,1,0), 1);

I need it rotate in world axis.

Answer 1

You need to transform the world space rotation vector to model space before applying the rotation. Vectors are transformed with inverse transpose of the matrix, i.e. v'=transpose(inverse(M))*v

Because models generally define model->world matrix you need to invert this to get world->model matrix. So you need to calculate v' = transpose(inverse(inverse(model_to_world)))*v = transpose(model_to_view)*v before applying the rotation. Also note that the w-component of the vector must be 0

Answer 2

You need to transform the world axis to your model's coordinate system first. You can do this by applying the model's current transformation matrix to the axis vector through multiplication; like so:

matrix.rotate(axis.mul(matrix), angle);