SGI Releases Open Inventor As Open Source

SGI has released Open Inventor (TM) 3D graphics toolkit to the open source community. You can read the press release here and their FAQ here. I'm sure many people will ask what is this Open Inventor, so could a /. reader give a few words about it?

Comments

Open Inventor

[Jonathan Blocksom]

I've done some stuff using Inventor in the past, here's a non-marketing person's overview. Open Inventor is a high-level 3D graphics API which sits on top of OpenGL. With Open Inventor a programmer can work with objects, materials and cameras in a scene graph framework rather than having to deal with polygons, color/texture/lighting/material calls, and transformation matrices in their own data structure. A scene graph is a big tree which contains everything in the scene, well suited for hierarchical models.

Open Inventor is great at rapidly creating interactive 3D applications. By 'interactive' I mean things where the user can get in and pick objects, move them around, etc. Open Inventor takes care of all the rendering and events for you and so it's pretty easy to get something up and running. Performance is good but not Inventor's main thrust -- so it'd be better to write something like a model or level editor in inventor than a first-person shooter.

I've seen Inventor used to create an architectural modeler with great effect; the author was really able to focus on the interface and not spend a lot of time reinventing the wheel for his underlying data structure. We considered using Inventor for the project that eventually became my children's 3D building blocks program, but there were licensing issues and we didn't think the performance would be there by the time we wanted to release it. If I were starting again today, I might reconsider.

Re:Offtopic, I know, but ...

[mav[LAG]]

How do you even get started doing 3D stuff? Both still images and animated 3D? I'm looking for cost-free stuff that isn't cripware to get started. I have a very strong math/physics background, so I have no problem describing equations of motion, but I haven't the faintest as to how to get started.

It depends. If you want to program still and animated 3D graphics, then you have quite a few choices. Here are a (tiny) subset of the ones I know:

• Here is a series of accessible tutorials on the mathematics and implementation of 3d graphics
• OpenGL is the API of choice for most platforms. Simple, clear and easy to understand. It does assume that you know what the basics are though.
• Mesa is a free workalike implementation of OpenGL for most platforms. Reading the source to the included demos is a good way to start learning.
• Python is a very good language with OpenGL bindings with which to start messing around. If C and C++ seem too tedious just for experimenting then try PyOpenGL. Python itself can be learned in a weekend after which the GL module is there to play around with.

If you're not interested in programming - just modelling and creating then check out:

• Povray - a flexible raytracer
• Blender - a modelling, animation and sequence editing suite
• Some examples of what is possible

All of these tools and references are free and work on Windows and Linux alike.

Also, how prohibitive is the hardware for this kind of thing?

All you need is a resonable midrange PC and a decent accelerator. A hardware-accelerated graphics card on your platform is a must to view complex 3D graphics at any kind of framerate. Vendors with good Linux support include include Ati, nVidia, Matrox and 3Dfx.

Open Open Inventor, from one of its developers

[Thagg]

I worked with Rikk Carey and Paul Strauss, and the rest of the Inventor team from '92 through the release of Inventor 1.0. There were wholescale changes after I left, but I think that my experience is worth sharing here.

Synopsis

Ultimately, Open Inventor is useful as a 3D prototyping tool. It's a great way to get a simple, interactive 3D program running quickly.

Beyond that, I don't think that it's particularly useful. It falls into the classic trap of 'jack of all trades, master of none'. There is nothing that it does particlarly well except prototyping; so there are no rich Inventor applications.

My experience with Inventor

When I started at Silicon Graphics working on Inventor, (or Scenario as it was called at the time) I was filled with optimism and excitement. This tool was going to make 3D ubiquitous. I had thought that the reason that there were so few 3D applications was that they were too hard to write; and that by building a generic high-level toolkit we could solve that problem.

The big problem ended up being that by building a high-level toolkit; you end up taking over the application. If you want to provide high-level functionality, you necessarily have to circumscribe the possible applications. You have to adopt the Inventor scene graph, nodes, and traversal. These may not be appropriate for your particular application, in fact, they are almost guaranteed not to be. You can extend Inventor by creating your own nodes, and several users have done that to get more performance; and a closer match between their application and the Inventor infrastructure -- but that's only a step along the way to creating your complete independent application IMHO.

There were great things about the Inventor development experience. I have never worked with as bright or dedicated a team of programmers as Carey, Strauss, Paul Isaacs, Nik Thompson, Dave Mott, Dave Immel, Josie Wernecke, and Alain Dumesney. I was in charge of backups, and it was not uncommon that almost every of the hundreds of source modules was changed in a day -- we were making large scale changes at an incredibly rapid pace as we prototyped, learned, and experimented. ILM was one of our beta-sites, and they got more out of Inventor than I ever thought that they would.

Inventor also cured me of C++. It seemed at first that C++ would be perfect for something like Inventor; but it was a near disaster IMHO (not shared by everyone on the team, I should point out.) C++ gives you some extra rope; but it quickly becomes tangled around your neck.

The biggest problem by far was nodes and traversals. You can think about them as two different dimensions. Nodes are things like cubes, cylinders, materials, colors, lights, and so on; while traversals are for rendering, bounding box calculation, printing, and the like. Nodes are the nouns, and traversals are the verbs.

C++ works for one-dimensional extensions, but we had to resort to a traditional function table to do this two-dimensional extension. It works, but it's a mess; and the language only got in the way instead of helping. This is only one of the many examples were the promise of C++ was not only not fulfilled, but was shown to be the exact opposite of what was promised; it hindered rather than helped.

Going forward

At Siggraph this year, there were no less than four scene graphs for Linux discussed during the Linux/OpenGL BOF meeting. I wish them luck, and hope that they find something useful in the Inventor source.