Open Inventor - Use

Use

OpenGL (OGL) is a low level library that takes lists of simple polygons and renders them as quickly as possible. To do something more practical like “draw a house”, the programmer must break down the object into a series of simple OGL instructions and send them into the engine for rendering. One problem is that OGL performance is highly sensitive to the way these instructions are sent into the system, requiring the user to know which instructions to send and in which order, and forcing them to carefully cull the data to avoid sending in objects that aren't even visible in the resulting image. For simple programs a tremendous amount of programming has to be done just to get started.

Open Inventor (OI) was written to address this issue, and provide a common base layer to start working with. Objects could be subclassed from a number of pre-rolled shapes like cubes and polygons, and then easily modified into new shapes. The “world” to be drawn was placed in a scene graph run by OI, with the system applying occlusion culling on objects in the graph automatically. OI also included a number of controller objects and systems for applying them to the scene, making common interaction tasks easier. Finally, OI also supplied a common file format for storing “worlds”, and the code to automatically save or load a world from these files. Basic 3D applications could then be written in a few hundred lines under OI, by tying together portions of the toolkit with “glue” code.

On the downside OI tended to be slower than hand-written code, as 3D tasks are notoriously difficult to make perform well without shuffling the data in the scene graph by hand. Another practical problem was that OI could only be used with its own file format, forcing developers to write converters to and from the internal system.