public void scale(float x, float y, float z) {
    //apply(x, 0, 0, 0,  0, y, 0, 0,  0, 0, z, 0,  0, 0, 0, 1);
    m00 *= x;  m01 *= y;  m02 *= z;
    m10 *= x;  m11 *= y;  m12 *= z;
    m20 *= x;  m21 *= y;  m22 *= z;
    m30 *= x;  m31 *= y;  m32 *= z;
  }