layout.cpp

void ofApp::draw(){
    ofSetColor(ofColor::white);
    ofNoFill();

    const int size = 20;
    const int qs[7] = {0,   1, -1, 0, 1, -1, 0};
    const int rs[7] = {-1, -1,  0, 0, 0,  1, 1};
    
    for (int i = 0; i < 7; i++) {
        int q = qs[i];
        int r = rs[i];
        double x = (sqrt(3.0) * q + (sqrt(3.0) / 2.0) * r) * size;
        double y = (3.0 / 2.0) * r * size;
        ofDrawCircle(x + center_p.x, y + center_p.y, size);
    }
}