oF で半球を描く

https://www.opengl.org/discussion_boards/showthread.php/159402-half-sphere のコードを oF 用に書き直したものですが以下の課題があります。

• てっぺんが穴空きになる
• 頂点情報しか無い

もう少しベターな方法があればぜひ教えて下さい！

ofVbo mHemisphere;

void ofApp::setup()
{
    const auto resolution_ = 256;
    const auto radius_ = 100.0;

    std::vector<ofVec3f> vertices_;

    for (auto i = 0; i < resolution_; ++i)
    {
        for (auto j = 0; j < resolution_; ++j)
        {
            vertices_.emplace_back(ofVec3f(
                radius_ * std::cos(j * 2 * M_PI / resolution_) * std::cos(i * M_PI / (2 * resolution_)),
                radius_ * std::sin(-i * M_PI / (2 * resolution_)),
                radius_ * std::sin(j * 2 * M_PI / resolution_) * std::cos(i * M_PI / (2 * resolution_))
            ));
        }
    }

    ofMesh mesh_;

    for (auto i = 0; i < resolution_ - 1; ++i)
    {
        for (auto j = 0; j < resolution_; ++j)
        {
            mesh_.addVertex(vertices_.at(i * resolution_ + j));            
            mesh_.addVertex(vertices_.at(i * resolution_ + (j + 1) % resolution_));            
            mesh_.addVertex(vertices_.at((i + 1) * resolution_ + (j + 1) % resolution_));            
            mesh_.addVertex(vertices_.at((i + 1) * resolution_ + j));
        }
    }

    mHemisphere.setMesh(std::move(mesh_), GL_STATIC_DRAW);
}

void ofApp::draw()
{
    ofTranslate(ofGetWidth() * 0.5, ofGetHeight() * 0.5);
    ofRotate(ofGetElapsedTimef() * 30.0, 1.0, 0.0, 1.0);
    mHemisphere.draw(GL_QUADS, 0, mVbo.getNumVertices());
}