Transform/multiply the given 2D-vector, as if it was a 3D-vector with z=0, by
this matrix and store the result in that vector.
<p>
The given 2D-vector is treated as a 3D-vector with its z-component being <code>0.0</code>, so it
will represent a direction in 2D-space rather than a position. This method will therefore
not take the translation part of the matrix into account.
<p>
In order to store the result in another vector, use {@link #transformDirection(Vector2d, Vector2d)}.
@see #transformDirection(Vector2d, Vector2d)
@param v
the vector to transform and to hold the final result
@return v
Transform/multiply the given 2D-vector, as if it was a 3D-vector with z=0, by this matrix and store the result in that vector. <p> The given 2D-vector is treated as a 3D-vector with its z-component being <code>0.0</code>, so it will represent a direction in 2D-space rather than a position. This method will therefore not take the translation part of the matrix into account. <p> In order to store the result in another vector, use {@link #transformDirection(Vector2d, Vector2d)}.
@see #transformDirection(Vector2d, Vector2d)
@param v the vector to transform and to hold the final result @return v