The dir changed since 2.0.

Generate a 4x4 transformation matrix which can pass into `multmatrix`

to mirror the child element on a plane through the origin.

**Since:** 1.1

## Parameters

`v`

: The normal vector of a plane intersecting the origin through which to mirror the object.

## Examples

```
use <matrix/m_mirror.scad>;
rotate([0, 0, 10])
cube([3, 2, 1]);
multmatrix(m_mirror([1, 1, 0]))
rotate([0, 0, 10])
cube([3, 2, 1]);
```