write an openFrameworks particle system

main.cpp

#include "ofMain.h"

class Particle {
public:
    ofPoint position;
    ofPoint velocity;
    float radius;
    ofColor color;

    Particle() {
        position.set(ofRandom(ofGetWidth()), ofRandom(ofGetHeight()));
        velocity.set(ofRandom(-10, 10), ofRandom(-10, 10));
        radius = ofRandom(3, 15);
        color.setHsb(ofRandom(255), 200, 200);
    }

    void update() {
        position += velocity;

        // Add a gravitational pull towards the center of the screen
        ofPoint center(ofGetWidth() / 2, ofGetHeight() / 2);
        ofPoint direction = center - position;
        float distance = direction.length();
        direction.normalize();
        float strength = 0.1;
        velocity += direction * strength;

        // Bounce off the edges of the screen
        if (position.x < 0 || position.x > ofGetWidth()) {
            velocity.x *= -1;
        }
        if (position.y < 0 || position.y > ofGetHeight()) {
            velocity.y *= -1;
        }
    }

    void draw() {
        ofSetColor(color);
        ofDrawCircle(position, radius);
    }
};

class ofApp : public ofBaseApp{
public:
    vector<Particle> particles;

    void setup() {
        ofBackground(0);
        for (int i = 0; i < 1000; i++) {
            particles.push_back(Particle());
        }
    }

    void update() {
        for (int i = 0; i < particles.size(); i++) {
            particles[i].update();
        }
    }

    void draw() {
        for (int i = 0; i < particles.size(); i++) {
            particles[i].draw();
        }
    }
};

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