Does anyone know of a simple yet flexible 2d scene graph in c++?

I'm searching a simple 2d scene graph written in c++, possibly on top of OpenGL but that's not mandatory: the perfect thing would be the Cocos2d/Cocos2d-iphone scenegraph in c++. Do you know of any existing implementations?

Solution

Here are a few ideas:

SGL - It is designed for 3D scene graphs, but also might support 2D. The website looks pretty informative.
Papyrus C++ Cairo Scenegraph Library

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