Advanced Omegalib/OSG Applications
Building visualizations with cyclops in python can produce stunning results and provides tools for many use cases, however there are certain applications which cannot be built with cyclops/python (without extending the cyclops c++ classes). The underlying framework OpenSceneGraph is a powerful general purpose computer graphics library, which omegalib/cyclops uses to render computer graphics distributed across multiple displays.
Reasons for programming in osg/omegalib in c++ could be
- You already have an existing application using osg that you want to port to a multi-display setup in omegalib
- Your application requires a large amount of data processing, dynamic geometry or special effects
- You want to use third party c++ libraries, such as physics or sound engines
- You want to use any methods of osg which are not accesible in cyclops
This tutorial assumes that you already have knowledge of programming in osg. If not, there are many good resources on the internet to learn programming the OpenSceneGraph, for example, the OpenSceneGraph Beginner’s Guide (http://ahux.narod.ru/olderfiles/1/OpenSceneGraph.3.0.Beginners.Guide-3208.pdf) will get you started and contains many good examples. Going further, the OpenSceneGraph Cookbook (https://www.packtpub.com/game-development/openscenegraph-3-cookbook) provides recipes for many advanced topics.
Integration of osg and omegalib
Omegalib comes with support for openscenegraph as its rendering system in form of the omegaOsg module. It is important to know, how osg is actually integrated into omegalib and how rendering on distributed nodes work, to be able to efficiently develop applications in omegalib. Unfortunately, there is no official documentation of the omegaOsg module, which leaves programmers with only the source code to work with. Luckily, the binding code between osg and omegalib is rather small and not too complex.
The omegaOsg module is a omegalib module which contains a osg::Node (the root) and registers a custom renderpass to the omegalib library. On each frame, the equalizer displaysystem calls the render method (on all nodes) of the renderpass class. Internally, the osgmodule copies over all transforms and properties of the omegalib camera to a osg::Camera and then the sceneview class performs the culling and rendering of the scenegraph. It is important to know, that no geometry is shared among nodes (in fact not even transforms are shared), the distributed nodes all run the same program and the renderloop execution is synced. Therefore transforms or dynamic geometry might have be synced by yourself. We will elaborate on this topic later again.