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Open Inventor, originally IRIS Inventor, is a C++ object oriented retained mode 3D graphics API designed by SGI to provide a higher layer of programming for OpenGL. Its main goals are better programmer convenience and efficiency.

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Early history

Around 1988–1989, Wei Yen asked Rikk Carey to lead the IRIS Inventor project. Their goal was to create a toolkit that made developing 3D graphics applications easier to do. The strategy was based on the premise that people were not developing enough 3D applications with IRIS GL because it was too time-consuming to do so with the low-level interface provided by IRIS GL. If 3D programming were made easier, through the use of an object oriented API, then more people would create 3D applications and SGI would benefit. Therefore, the credo was always “ease of use” before “performance”, and soon the tagline “3D programming for humans” was being used widely.

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.

TGS Open Inventor

Open Inventor was later opened for 3rd-party licensing, which is when it switched from “IRIS” to “Open“. It was licensed to two third party developers, Template Graphics Software and Portable Graphics. TGS later bought Portable Graphics, making them the sole licensee. In 2004 TGS was acquired by Mercury Computer Systems, and was known as Mercury's Visualization Sciences Group. In 2009, the Visualization Sciences Group became an independent entity called VSG, who continue to develop and support OI.

Performer

About a year into the Inventor project, a different philosophy began to emerge. Instead of simply making it easy to write applications on SGI systems, the goal was changed to make it difficult to write slow applications. Members of the Inventor team left to form their own group, which founded the basis of the OpenGL Performer project. Performer was also based on an internal scene graph, but was allowed to modify it for better speed as it saw fit, even dropping “less important” objects and polygons in order to maintain guaranteed performance levels. Performer also used a number of processes to run tasks in parallel for added performance, allowing it to be run (in one version) on multiple processors. Unlike Inventor, Performer remained proprietary so that SGI would have the agility to modify the API as needed to keep in step with the latest hardware enhancements.

Mid 1990s

At some point in the mid-1990s it was realized that there was no good reason that the two systems could not be combined, resulting in a single high-level API with both performance and programmability. SGI started work on yet another project aimed at merging the two, eventually culminating in Cosmo 3D. However Cosmo had a number of practical problems that could have been avoided with better design.

Eventually all of these ideas would come together to create the OpenGL++ effort, along with Intel, IBM and DEC. Essentially a cleaned up and more “open” version of Cosmo 3D, work on Cosmo ended and SGI turned to OpenGL++ full time. The OpenGL++ effort would drag on and eventually be killed, and SGI then tried again with Microsoft with the similar Fahrenheit project, which also died. During this time SGI ignored OI, and eventually spun it off completely to TGS.

Recent history

After many years of Inventor being solely available under proprietary licensing from TGS, it was released under an open source license in August 2000, which is available from SGI.

At approximately the same time, an API clone library called Coin3D was released by the company SIM (Systems in Motion). SIM was later acquired by the Kongsberg group and re-branded as Kongsberg SIM. The Coin library had been written in a clean room fashion from scratch, sharing no code with the original SGI Inventor library, but implementing the same API for compatibility reasons. Systems in Motion's Coin library is released under a dual licensing scheme, available both under the GNU GPL (for Free Software development) and a commercially sold license for proprietary software development.

The open source version from SGI has since fallen into obscurity, as SGI has not shown any commitment to do further development of the library, and seems to spend little resources even on maintenance.

Kongsberg SIM's Coin library and TGS's Inventor are still thriving under active development, and both have added numerous improvements to the original Inventor API like extensive support for the VRML standard.

Despite its age, the Open Inventor API is still widely used for a wide range of scientific and engineering visualization systems around the world, having proven itself well designed for effective development of complex 3D application software.

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