int v1(0); // 左上角
viewer->createViewPort(0.0, 0.5, 0.5, 1.0, v1);
int v2(0); // 右上角
viewer->createViewPort(0.5, 0.5, 1.0, 1.0, v2);
int v3(0); // 左下角
viewer->createViewPort(0.0, 0.0, 0.5, 0.5, v3);
int v4(0); // 右下角
viewer->createViewPort(0.5, 0.0, 1.0, 0.5, v4);