ss3d: skinned mesh matrix calculation

boneData = _R.AnimMesh.boneData;
animmi.resizeSkinMatrixArray( map_size( boneData ) );
i0 = boneData[0].inv_skin_offset;
i1 = boneData[1].inv_skin_offset;
o0 = boneData[0].bone_offset;
o1 = boneData[1].bone_offset;
r0 = mat4().rotateX(deg2rad(30));
r1 = mat4().rotateX(deg2rad(60));
f0 = mat4().multiply2( mat4().multiply2( i0, r0 ), o0 );
f1 = mat4().multiply2( mat4().multiply2( mat4().multiply2( i1, r1 ), o1 ), f0 );
animmi.setSkinMatrix( 0, f0 );
animmi.setSkinMatrix( 1, f1 );