// XYZ to HPB rotation.
vector xyz_to_hpb(matrix M)
{
    vector tmp = 0;
    tmp.x = atan2(M.zx, M.zz);
    tmp.y = atan2(M.zy, sqrt(M.zx * M.zx + M.zz * M.zz));
    tmp.z = atan2(M.xy, M.yy);
    return tmp;
}

// HPB to XYZ rotation (requires an hpb-orientated matrix).
vector hpb_to_xyz(matrix M)
{
    vector tmp = 0;
    tmp.x = atan2(M.yz, M.zz);
    tmp.y = atan2(-M.xz, sqrt(M.xy * M.xy + M.xx * M.xx));
    tmp.z = atan2(M.xy, M.xx);
    return tmp;
}

// xform components.
vector t    = chv("t");
vector r    = chv("r");
vector s    = chv("s");
float scale = chf("scale");

// Create matrix from xfrom components.
matrix M = maketransform(0, 0, t, r, s * scale);

// XYZ to HPB rotation.
v@HPB_rot = degrees(xyz_to_hpb(M));

// Apply matrix to Points.
@P *= M;