Implement transform.Rotate using rotation matrix - unity3d

Question

I'm trying to implement transform.Rotate on the y axis in Unity using rotation matrix, is it possible? I wrote this function but it doesn't seems to work, pos is the position of the object to rotate and theta is the angle
public static MyQuaternion Rotate(Vector3 pos, float theta)
{
pos = pos.normalized;
pos -= pos;
float[,] m = new float[3, 3];
m[0, 0] = Mathf.Cos(theta);
m[0, 1] = 0;
m[0, 2] = Mathf.Sin(theta);
m[1, 0] = 0;
m[1, 1] = 1;
m[1, 2] = 0;
m[2, 0] = -Mathf.Sin(theta);
m[2, 1] = 0;
m[2, 2] = Mathf.Cos(theta);
Vector3 newPos = new Vector3();
float temp;
for (int i = 0; i < 3; ++i)
{
temp = 0;
for (int j = 0; j < 3; ++j)
{
temp += m[i, j] * pos[j];
}
newPos[i] = temp;
}
newPos += pos;
return new MyQuaternion(newPos.x, newPos.y, newPos.z, 0);
}
Do you have any idea? Thanks

Answer 1

If you want to get deeply into rotating a vector by hand, you are sort of doing it all right, however I am not sure about the type MyQuaternion you are returning.
If you just want to rotate a vector by an arbitrary angle you can just use Unity's build in Quaternion class. The mutliplication by Vector3 is defined as rotation of that vector so you can just do
Quaternion q=Quaternion.Euler(theta,0,0); // or however you want to map it
Vector3 rotatedVector=q*inputVector;
return rotatedVector;
Rotation in unity is generally done via Quaternion multiplication. To apply it to a gameobject, simply multiply its transform by a rotation you want to perform.
transform.rotation*=Quaternion.Euler(0,0,theta);
Position of an object does not have any play in rotation.