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POGenerating an interface without virtual functions?
 

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  1. POGenerating an interface without virtual functions?
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    <p>I'm coding a game engine and I have this class set up for objects:</p> <pre><code>class SceneManager //controls everything in the "world" game { public: void Add(SceneObject* object); //adds to the vector private: vector&lt;SceneObject*&gt; _worldObjects; //the vector that contains all of them } </code></pre> <p>And all classes I work on the game inherit from SceneObject:</p> <pre><code>class SceneObject { public: virtual void Draw() = 0; } class Image : public SceneObject { } class Sprite : public SceneObject { } class Model3D : public SceneObject { } </code></pre> <p>So I know I can call Draw() for all objects in my vector. But I've been working on optimizations and I'm trying to get rid of all inheritance and virtual functions, and use composition instead, since they can't be inlined and seems to be a major performance issue when performed on a per-object basis.</p> <p>I'm looking for some C++ technique that I can use to be able to store a bunch of SceneObjects in my vector, and then call Draw() on it and it properly draws the object related to it. This will also work for the Update() function I'm using as virtual.</p> <p>So this code:</p> <pre><code>void SceneManager::Add(SceneObject* object) { _worldObjects.push_back(object); } void SceneManager::DrawTheWorld() { for(unsigned int i = 0; i &lt; _worldObjects.size(); i++) { _worldObjects[i]-&gt;Draw(); //SceneObject's being called } } </code></pre> <p>...would become:</p> <pre><code>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 &lt; _worldObjects.size(); i++) { //_worldObjects[i]-&gt; //I need somehow to be able to get the pointer back to the original class //It can be an image, sprite, model3d, anything } } </code></pre> <p>I don't think if I add a switch or if/elses and removing the virtual I'd gain any performance, so I'm trying to figure if there's a clean way to deal with this.</p> <p>Any ideas?</p>
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    1. USKonrad Rudolph
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      1. USMohamad Ali Baydoun
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    1. COyou should watch the last part of [Seasoning C++](http://channel9.msdn.com/Events/GoingNative/2013/Cpp-Seasoning) by Sean Parent
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    2. CODoes the call itself add that much overhead to bother about it? Have you profiled?
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      1. USLuchian Grigore
    3. COI suspect memory locality is more important than the virtual call overheads. For example, if you can keep the collection mostly sorted by type, and perhaps have pools of same-type objects, it could improve performance a lot - mainly because of the instruction cache and maybe some branch prediction improvements, but also because of locality of access to virtual tables and the objects. It may even make sense to move the "hottest" fields out of the objects to separate arrays.
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