The new generation of OpenGL support in ROOT

OpenGL has been promoted to become the main 3D rendering engine of the ROOT framework. This required a major re-modularization of OpenGL support on all levels, from basic window-system specific interface to medium-level object-representation and top-level scene management. This new architecture allows seamless integration of external scene-graph libraries into the ROOT OpenGL viewer as well as inclusion of ROOT 3D scenes into external GUI and OpenGL-based 3D-rendering frameworks. Scene representation was removed from inside of the viewer, allowing scene-data to be shared among several viewers and providing for a natural implementation of multi-view canvas layouts. The object-graph traversal infrastructure allows free mixing of 3D and 2D-pad graphics and makes implementation of ROOT canvas in pure OpenGL possible. Scene-elements representing ROOT objects trigger automatic instantiation of user-provided rendering-objects based on the dictionary information and class-naming convention. Additionally, a finer, per-object control over scene-updates is available to the user, allowing overhead-free maintenance of dynamic 3D scenes and creation of complex real-time animations. User-input handling was modularized as well, making it easy to support application-specific scene navigation, selection handling and tool management