Section: Application Domains

Virtual Reality

Participants : Thierry Gautier, Bruno Raffin, Jean-Louis Roch.

We are pursuing and extending existing collaborations to develop virtual reality applications on PC clusters and grid environments:

• Real time 3D modeling. An on-going collaboration with the MORPHEO project focuses on developing solutions to enable real time 3D modeling from multiple cameras using a PC cluster. An operational code base was transferred to the 4DViews Start-up in September 2007. 4DViews is now selling turn key solutions for real-time 3D modeling. Recent developments take two main directions:

  • Using a HMD (Head Mounted Display) and a Head Mounted Camera to provide the user a high level of interaction and immersion in the mixed reality environment. Having a mobile camera raises several concerns. The camera position and orientation need to be precisely known at anytime, requiring to develop on-line calibration approaches. The background subtraction cannot anymore be based on a static background learning for the mobile camera, required here too new algorithms.

  • Distributed collaboration across distant sites. In the context of the ANR DALIA we are developing a collaborative application where a user at Bordeaux (iParla project-team) using a real time 3D modeling platform can meet in a virtual world with a user in Grenoble also using a similar platform. We rely on the Grid'5000 dedicated 10 Gbits/s network to enable a low latency. The main issues are related to data transfers that need to be carefully managed to ensure a good latency while keeping a good quality, and the development of new interaction paradigms.

  On these issues, Benjamin Petit started a Ph.D. in October 2007, co-advised by Edmond Boyer (PERCEPTION) and Bruno Raffin.

• Real time physical simulation. We are collaborating with the EVASION project on the SOFA simulation framework. Everton Hermann, a Ph.D. co-advised by François Faure (EVASION) and Bruno Raffin, works on parallelizing SOFA using the KAAPI programming environment. The challenge is to provide SOFA with a parallelization that is efficient (real-time) while not being invasive for SOFA programmers (usually not parallel programmer). We developed a first version using the Kaapi environment for SMP machines that relies on a mix of work-stealing and dependency graph analysis and partitioning. A second version targets machines with multiples CPUs and multiple GPUs. We extended the initial framework to support a work stealing based load balancing between CPUs and GPUs. It required to extend Kaapi to support heterogeneous tasks (GPU and CPU ones) and to adapt the work stealing strategy to limit data transfers between CPUs and GPUs (the main bottleneck for GPU computing).

• Distant collaborative work. We conduct experiments using FlowVR for running applications on Grid environments. Two kinds of experiments will be considered: collaborative work by coupling two or more distant VR environments ; large scale interactive simulation using computing resources from the grid. For these experiments, we are collaborating with the LIFO and the LABRI.

• Parallel cache-oblivious algorithms for scientific visualization. In collaboration with the CEA DAM, we have developed a cache-oblivious algorithm with provable performance for irregulars meshes. Based on this work, we are studying parallel algorithms that take advantage of the shared cache usually encountered on multi-core architectures (L3 shared cache). The goal is to have the cores collaborating to efficiently share the L3 cache for a better performance than with a more traditional approach that leads to split the L3 cache between the cores. We are obtaining good performance gains with a parallel iso-surface extraction algorithm. This work is the main focus of Marc Tchiboukdjian Ph.D.