protected void lightPosition(int num, float x, float y, float z) {
    lightPositionVec.set(x, y, z);
    modelview.mult(lightPositionVec, lightPosition[num]);
    /*
    lightPosition[num][0] =
      modelview.m00*x + modelview.m01*y + modelview.m02*z + modelview.m03;
    lightPosition[num][1] =
      modelview.m10*x + modelview.m11*y + modelview.m12*z + modelview.m13;
    lightPosition[num][2] =
      modelview.m20*x + modelview.m21*y + modelview.m22*z + modelview.m23;
    */
  }