Set this matrix to a rotation transformation about the Z axis to align the local <code>+X</code> towards <code>(dirX, dirY)</code>.
<p>
The vector <code>(dirX, dirY)</code> must be a unit vector.
@param dirX
the x component of the normalized direction
@param dirY
the y component of the normalized direction
@return this
Set this matrix to a rotation transformation about the Z axis to align the local <code>+X</code> towards <code>(dirX, dirY)</code>. <p> The vector <code>(dirX, dirY)</code> must be a unit vector.
@param dirX the x component of the normalized direction @param dirY the y component of the normalized direction @return this