ConvexHull in openFrameworks

ConvexHull.cpp

//by Rick Companje
//based on Greg Borenstein's https://github.com/atduskgreg/Processing-Convex-Hull

#include "ofMain.h"

bool lexicalComparison(const ofPoint& v1, const ofPoint& v2) {
  if (v1.x > v2.x) return true;
  else if (v1.x < v2.x) return false;
  else if (v1.y > v2.y) return true;
  else return false;
}

class ofApp : public ofBaseApp {
public:
  
  vector<ofPoint> points,hull;
  ofPoint h1,h2,h3;
  int currentPoint,direction;
  
  void setup() {
    ofSetFrameRate(30);
  }
  
  void update() {

  }
  
  void draw() {
    ofSetColor(255);
    ofFill();
    for (int i=0; i<points.size(); i++) {
      ofCircle(points.at(i),2);
    }
    
    ofNoFill();
    ofBeginShape();
    for (int i=0; i<hull.size(); i++) {
      ofVertex(hull.at(i));
    }
    ofEndShape();
  }
  
  void mouseDragged(int x, int y, int button) {
    points.push_back(ofPoint(x,y));
  }
  
  void mouseReleased(int x, int y, int button) {
    hull = getConvexHull(points);
  }

  bool isRightTurn(ofPoint a, ofPoint b, ofPoint c) {
    // use the cross product to determin if we have a right turn
    return ((b.x - a.x)*(c.y - a.y) - (b.y - a.y)*(c.x - a.x)) > 0;
  }
  
  vector<ofPoint> getConvexHull(vector<ofPoint> points) {
    sort(points.begin(), points.end(), lexicalComparison);
    
    vector<ofPoint> hull;

    hull.push_back(points.at(0));
    hull.push_back(points.at(1));
    
    int currentPoint = 2;
    int direction = 1;
    
    for (int i=0; i<1000; i++) { //max 1000 tries
      
      hull.push_back(points.at(currentPoint));
      
      // look at the turn direction in the last three points
      h1 = hull.at(hull.size()-3);
      h2 = hull.at(hull.size()-2);
      h3 = hull.at(hull.size()-1);
      
      // while there are more than two points in the hull
      // and the last three points do not make a right turn
      while (!isRightTurn(h1, h2, h3) && hull.size() > 2) {

        // remove the middle of the last three points
        hull.erase(hull.end() - 2);
        
        if (hull.size() >= 3) {
          h1 = hull.at(hull.size()-3);
        }
        h2 = hull.at(hull.size()-2);
        h3 = hull.at(hull.size()-1);
      }
      
      // going through left-to-right calculates the top hull
      // when we get to the end, we reverse direction
      // and go back again right-to-left to calculate the bottom hull
      if (currentPoint == points.size() -1 || currentPoint == 0) {
        direction = direction * -1;
      }
      
      currentPoint+= direction;
     
      if (hull.front()==hull.back()) break;
    }
    
    return hull;
  }
  
  
  void keyPressed(int key) {
    if (key=='c') {
      ofBackground(0);
      points.clear();
      hull.clear();
    }
  }
  
};

int main( ){
  ofSetupOpenGL(1024,768,OF_WINDOW);
  ofRunApp(new ofApp());
}

the isRightTurn function should use > sign instead of >=.
Update: fixed