Openframeworks draw cirlces

Circle.cpp

#include "Circle.h"

Circle::Circle(float x, float y, float r)
{
    _x = x;
    _y = y;
    _r = r;
    
    _color.r = ofRandom(255);
    _color.g = ofRandom(255);
    _color.b = ofRandom(255);
    _color.a = 255;
    
    _isDestroy = false;
}

Circle::~Circle()
{
}

bool Circle::isDestroy()
{
    return _isDestroy;
}

void Circle::draw()
{
    if (0 >= _color.a) {
        _isDestroy = true;
        return;
    }
    
    ofSetColor(_color);
    ofCircle(_x, _y, _r);
    
    _color.a -= 1;
}

Circle.h

#pragma once

#include "ofMain.h"

class Circle
{
public:
    Circle(float x, float y, float r);
    ~Circle();
    void draw();
    
    bool isDestroy();
    
private:
    float _x;
    float _y;
    float _r;
    
    ofColor _color;
    
    bool _isDestroy;
};

main.cpp

#include "ofMain.h"
#include "ofApp.h"

//========================================================================
int main( ){
	ofSetupOpenGL(200, 200, OF_WINDOW);			// <-------- setup the GL context

	// this kicks off the running of my app
	// can be OF_WINDOW or OF_FULLSCREEN
	// pass in width and height too:
	ofRunApp(new ofApp());

}

ofApp.cpp

#include "ofApp.h"
#include <math.h>

#define WIDTH 200
#define HEIGHT 200
#define CIRCLE_RADIUS 10

void ofApp::setup()
{
    ofSetFrameRate(60);
    
    ofSetWindowShape(WIDTH, HEIGHT);

    _x = 0;
    _y = 0;
}

void ofApp::update()
{
}

void ofApp::draw()
{
    for (std::vector<Circle *>::iterator it = _circles.begin(); it != _circles.end();) {
        Circle *circle = (*it);
        if (circle->isDestroy()) {
            it = _circles.erase(it);
            delete circle;
            continue;
        }
        circle->draw();
        
        it++;
    }
}

void ofApp::mouseMoved(int x, int y)
{
    float distance = sqrt(pow((_x - x), 2) + pow((_y - y), 2));
    
    if ((CIRCLE_RADIUS * 2) > distance) {
        return;
    }

    _x = x;
    _y = y;

    _circles.push_back(new Circle(_x, _y, CIRCLE_RADIUS));
}

ofApp.h

#pragma once

#include "ofMain.h"
#include "./Circle.h"

class ofApp : public ofBaseApp
{
public:
    std::vector<Circle *> _circles;
    
    float _x;
    float _y;
    
public:
    void setup();
    void update();
    void draw();
    
    void mouseMoved(int x, int y);
};