Question

在下面的代码中，我尝试在复合对象中绘制一个圆形对象，但它不会绘制。我不知道为什么。此代码永远不会达到圆绘制方法。

如果我直接在main.cpp中调用circle的draw（）方法，它将绘制..

drawable.h

#pragma once

#include <SFML/Graphics.hpp>

class drawable{
  public:
   drawable(sf::Vector2f position);
   virtual void draw(sf::RenderWindow & window){};
   sf::Vector2f position;
};

class circle : public drawable{
  public:
   circle(sf::Vector2f position);
   void draw(sf::RenderWindow & window) override;
};

class composite : public drawable{
  public:
   composite(sf::Vector2f position, drawable part);
   void draw(sf::RenderWindow & window) override;
  private:
   int count = 0;
   drawable part;
};

drawable.cpp

#include "drawable.h"

#include <iostream>
using namespace std;

drawable::drawable(sf::Vector2f position) : position{ position } {
}

circle::circle(sf::Vector2f position) : drawable{ position } {
}

composite::composite(sf::Vector2f position, drawable part) : drawable(position), part{ part }{
}

void circle::draw(sf::RenderWindow & window) {
  sf::CircleShape circle;
  circle.setPosition(position);
  circle.setRadius(30);
  window.draw(circle);
}

void composite::draw(sf::RenderWindow & window) {
  this->part.position.x = this->position.x + part.position.x;
  this->part.position.y = this->position.y + part.position.y;
  this->part.draw(window);
}

main.cpp

#include <SFML/Graphics.hpp>
#include "drawable.h"

int main()
{
  sf::RenderWindow window = sf::RenderWindow{ sf::VideoMode{ 640, 480 }, "SFML window" };

  circle circle{ sf::Vector2f{ 100, 200 } };
  composite composite(sf::Vector2f{ 200, 200 }, circle);

  window.clear();   
  composite.draw(window);
  window.display();

  while (window.isOpen()) {
    sf::Event event;
    while (window.pollEvent(event)){
        if (event.type == sf::Event::Closed){
            window.close();
        }
    }
    sf::sleep(sf::milliseconds(20));
  }

  return 0;
}

Answer 1

Composite按值drawable获取。这意味着在composite内，您只能获得drawable个对象;有关混凝土类型的所有信息都将丢失。如果要支持多态对象，则需要使用指针或引用。

C ++ SFML对象不会绘制

1 个答案: