Question

In my C# game engine, I used to handle ordered drawing by adding/removing action to a manager object, which sorted the actions by priority, then executed them.

Here is a very simplified example:

class DrawManager
{
    public List<Tuple<Action, int>> DrawActions = new List<Tuple<Action, int>>();
    void Draw() { foreach (var tuple in DrawActions) tuple.Item1(); }
}

class Example
{
    DrawManager manager;

    Example()
    {
        manager.DrawActions.Add(new Tuple<Action, int>(DrawBackground, 0));
        manager.DrawActions.Add(new Tuple<Action, int>(DrawForeground, 100));
    }
    ~Example()
    {
        manager.DrawActions.Remove(manager.DrawActions.Find(x => x.Item1 == DrawBackground));
        manager.DrawActions.Remove(manager.DrawActions.Find(x => x.Item1 == DrawForeground));
    }

    void DrawBackground() { /* draw something */ }
    void DrawForeground() { /* draw something */ }
}

By adding some helper methods, the code becomes very elegant and easy to use in my engine.

I’ve moved to C++ recently, and I can’t find any easy way to achieve the same result.

I tried using std::function, but in order to remove the method on object destruction, I had to store the draw method in a pointer owned by the caller, then wrap it into a lambda and pass it in. Very inelegant and time consuming.

Is there any way to get code similar to the one shown in the C# example?

Answer 1

You can use std::function in place of Action:

typedef std::function<void()> Action;
std::vector<std::pair<Action, int> > DrawActions;
void Draw() {
    for_each(DrawActions.begin(), DrawActions.end(), [](std::pair<Action, int>& a) {
       a.first(); 
    });
}