You can use free functions to model the drawable
aspect of your objects:
#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"; }
}
Now, either use three separate vectors (this could well be most optimal, depending on the ordering relationship between the objects across collections?), or consider a variant type vector:
1. Using variant types
#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);
}
}
A complete proof of concept of the latter: Live on 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);
}
Outputs
drawing image
drawing sprite
drawing model3D
drawing image
2. Separate collections
The alternative using separate vectors: 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);
}
Note that the output is different (ordering):
drawing image
drawing image
drawing sprite
drawing model3D