Determining roll, pitch, and yaw from a normalized vector

[Andy]

You can use something like this:

Prototype void person_turn_left(Person *person, float angle) //angle in degrees 
{
float m[16], m2[16];

	matrix4_set_rotation(-angle, 0, 1, 0, m);
	matrix4_multiply(m2, person->matrix, m);
	matrix4_copy(person->matrix, m2);
	person_set_direction_from_matrix(person);
}

Prototype void person_set_direction_from_matrix(Person *person)
{
	person->direction.x= person->matrix[2]; 
	person->direction.y= person->matrix[6];
	person->direction.z= person->matrix[10];
}

gluLookat is used to setup the 'camera' viewpoint in OpenGL, You pass it a location and a direction (which can be location + direction) and OpenGL does all the stuff to set the viewing matrix.

Andy