At the very top of the diagram is the Root object. This is your 'way in' to the OGRE system, and it's where you tend to create the top-level objects that you need to deal with, like scene managers, rendering systems and render windows, loading plugins, all the fundamental stuff. If you don't know where to start, Root is it for almost everything, although often it will just give you another object which will actually do the detail work, since Root itself is more of an organiser and facilitator object. The majority of rest of OGRE's classes fall into one of 3 roles:
- Scene Management
- This is about the contents of your scene, how it's structured, how it's viewed from cameras, etc. Objects in this area are responsible for giving you a natural declarative interface to the world you're building; ie you don't tell OGRE "set these render states and then render 3 polygons", you tell it "I want an object here, here and here, with these materials on them, rendered from this view", and let it get on with it. Resource Management
- All rendering needs resources, whether it's geometry, textures, fonts, whatever. It's important to manage the loading, re-use and unloading of these things carefully, so that's what classes in this area do. Rendering
- Finally, there's getting the visuals on the screen - this is about the lower-level end of the rendering pipeline, the specific rendering system API objects like buffers, render states and the like and pushing it all down the pipeline. Classes in the Scene Management subsystem use this to get their higher-level scene information onto the screen.