Coordinate conversion

UniVRM convert coordinate when import or export

	right	up	forward	chirality	Origin of Texture coordinates
Unity	+X	+Y	+Z	Left handed	left bottom
VRM-0	+X	+Y	-Z	Right handed	left top
VRM-1	-X	+Y	+Z	Right handed	left top
glTF		+Y		Right handed	left top	The default is the VRM-0 method. Vrm-1 method can be selected as an option

UV

The following conversions

\[V^{\prime} = 1 - V\]

Unity <-> VRM0

Invert Z-axis

Vector3: Position, Normal, etc.

public static Vector3 ReverseZ(this Vector3 v)
{
    return new Vector3(v.x, v.y, -v.z);
}

Quaternion: Rotation

public static Quaternion ReverseZ(this Quaternion q)
{
    float angle;
    Vector3 axis;
    q.ToAngleAxis(out angle, out axis);
    return Quaternion.AngleAxis(-angle, ReverseZ(axis));
}

Matrix: BindMatrices

If the scale value is in it, it does not work.

public static Matrix4x4 ReverseZ(this Matrix4x4 m)
{
#if UNITY_2017_1_OR_NEWER
    m.SetTRS(m.GetColumn(3).ReverseZ(), m.rotation.ReverseZ(), Vector3.one);
#else
    m.SetTRS(m.ExtractPosition().ReverseZ(), m.ExtractRotation().ReverseZ(), Vector3.one);
#endif
    return m;
}

Unity <-> VRM1

Invert X-axis