生成没有虚函数的接口？

Question

我正在编写一个游戏引擎,我为对象设置了这个类:

class SceneManager //controls everything in the "world" game
{
    public:
        void Add(SceneObject* object); //adds to the vector
    private:
        vector<SceneObject*> _worldObjects; //the vector that contains all of them
}

我在游戏上工作的所有类都继承自SceneObject:

class SceneObject
{
    public: 
        virtual void Draw() = 0;
}

class Image : public SceneObject
{ }
class Sprite : public SceneObject
{ }
class Model3D : public SceneObject
{ }

所以我知道我可以为我的向量中的所有对象调用Draw().但我一直致力于优化,我正在尝试摆脱所有继承和虚函数,而是使用组合,因为它们无法内联,并且在每个对象上执行时似乎是一个主要的性能问题基础.

我正在寻找一些C++技术,我可以使用它来在我的向量中存储一堆SceneObjects,然后在它上面调用Draw()并正确绘制与之相关的对象.这也适用于我用作虚拟的Update()函数.

所以这段代码:

void SceneManager::Add(SceneObject* object)
{
    _worldObjects.push_back(object);
}
void SceneManager::DrawTheWorld()
{
    for(unsigned int i = 0; i < _worldObjects.size(); i++)
    {
        _worldObjects[i]->Draw(); //SceneObject's being called
    }
}

...会成为:

void SceneManager::Add(Image* image)
{
    SceneObject* object = new SceneObject();
    //link object to image somehow, tried to use it as a member of image
    _worldObjects.push_back(object);
}
void SceneManager::DrawTheWorld()
{
    for(unsigned int i = 0; i < _worldObjects.size(); i++)
    {
        //_worldObjects[i]->
        //I need somehow to be able to get the pointer back to the original class
        //It can be an image, sprite, model3d, anything
    }
}

我不认为如果我添加一个开关或if/elses并删除虚拟我会获得任何性能,所以我想弄清楚是否有一个干净的方法来处理这个问题.

有任何想法吗？

Answer 1

您可以使用自由函数来建模drawable对象的方面:

#include <iostream>

class Image { };
class Sprite { };
class Model3D { };

namespace draw_aspect
{
    void draw(Image const& image)     { std::cout << "drawing image\n";   } 
    void draw(Sprite const& sprite)   { std::cout << "drawing sprite\n";  } 
    void draw(Model3D const& model3D) { std::cout << "drawing model3D\n"; } 
}

现在,要么使用三个单独的向量(这可能是最优的,取决于跨集合的对象之间的排序关系？),或者考虑变量类型向量:

1.使用变体类型

#include <boost/variant.hpp>
using SceneObject = boost::variant<Image, Sprite, Model3D>;

namespace draw_aspect {    

    struct draw_visitor : boost::static_visitor<> {
        template <typename T> void operator()(T const& t) const { draw(t); }
    };

    void draw(SceneObject const& sobj) { 
        static const draw_visitor _vis;
        boost::apply_visitor(_vis, sobj);
    }
}

完整的后者概念证明:住在Coliru

#include <vector>

class SceneManager //controls everything in the "world" game
{
    public:
        void Add(SceneObject v) { _worldObjects.emplace_back(std::move(v)); }
        friend void draw(SceneManager const& sm) { return sm.draw(); }
    private:
        void draw() const {
            for(auto& sobj : _worldObjects)
                draw_aspect::draw(sobj);
        } 
        std::vector<SceneObject> _worldObjects; //the vector that contains all of them
};

int main()
{
    SceneManager sman;

    sman.Add(Image());
    sman.Add(Sprite());
    sman.Add(Model3D());
    sman.Add(Image());

    draw(sman);
}

输出

drawing image
drawing sprite
drawing model3D
drawing image

2.分开收藏

使用单独载体的替代方案:Live on Coliru

class SceneManager //controls everything in the "world" game
{
    public:
        void Add(Image v)   { _images  .emplace_back(std::move(v)); }
        void Add(Sprite v)  { _sprites .emplace_back(std::move(v)); }
        void Add(Model3D v) { _model3Ds.emplace_back(std::move(v)); }

        friend void draw(SceneManager const& sm) { return sm.draw(); }
    private:
        void draw() const {
            for(auto& sobj : _images)   draw_aspect::draw(sobj);
            for(auto& sobj : _sprites)  draw_aspect::draw(sobj);
            for(auto& sobj : _model3Ds) draw_aspect::draw(sobj);
        } 
        std::vector<Image> _images;
        std::vector<Sprite> _sprites;
        std::vector<Model3D> _model3Ds;
};

int main()
{
    SceneManager sman;

    sman.Add(Image());
    sman.Add(Sprite());
    sman.Add(Model3D());
    sman.Add(Image());

    draw(sman);
}

请注意,输出不同(排序):

drawing image
drawing image
drawing sprite
drawing model3D