Advanced 3-D Graphics: GNU Maverik—a VR Micro-Kernel
What we have gained is the flexibility to plug together quite different applications within a single VE framework, without compromising performance. That is a gain, but seems to be at the expense of having the application (and application programmer) do all the hard work. However, because Maverik is a framework into which things can be plugged with little performance loss, it is easy to provide commonly useful facilities and objects to get many applications off the ground. For example, Maverik is distributed with libraries of common geometric primitives, cones, cylinders, teapots, an animated avatar, sample graphics file parsers, navigation facilities, 3-D math functions, quarternion codes, stereo, 3-D peripheral drivers for head-mounted display and 3-D mice (see Figure 7) and so forth). If these are useful, then you use them as a good starting point. If they are not, then you provide your own objects and algorithms, perhaps refining the samples provided.
This makes it fairly straightforward to get started using the system. In practice, this gives three levels of increasingly sophisticated use.
Using the default objects and algorithms provided. Used this way, Maverik looks like a VR building package for programmers. The tutorial documentation for the system leads one through the building of an environment with behaviour, collision detection and customized navigation.
Defining your own classes of objects. This is where you benefit from application-specific optimizations that you could supply by providing your own rendering and associated callbacks. The tutorial gives an example of this, and the supplied demonstration applications make extensive use of the techniques. Unfortunately, the offshore platform example uses commercially sensitive data, so cannot be supplied with the distribution.
Extension and modification of the Maverik kernel. Rendering and navigation callbacks are one set of facilities that can be customized. For the adventurous, more of the Maverik core functionality is also up for grabs: for example, alternate culling strategies, spatial management structures and input device support. But this still takes place within the context of a consistent framework that seems to make it easy to plug different parts together.
The real test for Maverik as a research vehicle is how well it allows such pieces to fit into the overall puzzle. The hope is that it will make the task of building VEs “as hard as it should be”, avoiding the feeling that one's efforts are mostly spent “fighting the system”. So far, given a little familiarity with the approach, this looks very promising.
Recent Maverik developments include a novel force-field navigation algorithm to guide participants around obstacles, and an algorithm for probing geometry ahead of a user to test whether it can be climbed—for example, ladders and steps (see Figure 8). These algorithms integrate into Maverik, but at the time of this writing are released as separate beta sources for testing.
Maverik has no support for audio or video within it. You will need to add your favourite mechanism for those yourself.
Maverik is a single-user VE micro-kernel. It does not include any assistance for running multiple VEs on different machines for sharing a world between people. To do that, you would need to synchronize the VEs yourself across the network. For just navigating around a shared VE, that's not so hard. Running a system with many users across wide area networks with multiple VEs, applications, interaction and behaviour is a more complex challenge. It's a challenge we are working on now with a complementary system that uses Maverik. We aim to release what we have on that under the GNU GPL license later this year.
We are very keen to know how well these ideas work, or don't work, for other people—particularly those with experience of graphics programming. That way, we get to understand more about this whole area. Feedback should be addressed to firstname.lastname@example.org.
Adrian West (email@example.com) lectures on computer science at the University of Manchester, U.K. He is part of the Advanced Interfaces Research Group, working on systems architectures for distributed virtual environments.
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