Opticks : GPU Optical Photon Simulation for Particle Physics using NVIDIA® OptiXTM

Opticks is an open source project that integrates the NVIDIA OptiX GPU ray tracing engine with Geant4 toolkit based simulations. Massive parallelism brings drastic performance improvements with optical photon simulation speedup expected to exceed 1000 times Geant4 with workstation GPUs. Optical physics processes of scattering, absorption, scintillator reemission and boundary processes are implemented as CUDA OptiX programs based on the Geant4 implementations. Wavelength-dependent material and surface properties as well as inverse cumulative distribution functions for reemission are interleaved into GPU textures providing fast interpolated property lookup or wavelength generation. OptiX handles the creation and application of a choice of acceleration structures such as boundary volume hierarchies and the transparent use of multiple GPUs. A major recent advance is the implementation of GPU ray tracing of complex constructive solid geometry shapes, enabling automated translation of Geant4 geometries to the GPU without approximation. Using common initial photons and random number sequences allows the Opticks and Geant4 simulations to be run point-by-point aligned. Aligned running has reached near perfect equivalence with test geometries.

Comparison of Acceleration Data Structures for High Quality Fast Reflections of Static and Deformable Models in Walkthrough Animations

In order to render realistic images, the reflectance of surfaces must be simulated accurately. Generally, the ray tracing rendering technique is used to make a material reflect its surroundings, since it represents with great fidelity the behavior of light. However, ray tracing is still a very costly algorithm, so far mostly indicated in offline rendering scenarios. This situation is even more challenging for scenes containing 3D deformable meshes, since their geometry and, thus, the acceleration structures used, need to be updated in each frame of the animation. In this paper, we present an extended version of our hybrid algorithm that combines rasterization and a pure ray tracing through the NVIDIA OptiX to render high quality fast reflections, including scenes with deformable models. Additionally, we analyze and compare the performances of different NVIDIA OptiX acceleration data structures for generating reflections of static and deformable models in walkthrough animations. The results show that NVIDIA OptiX acceleration structures reach high frames per second for static objects. However, there is a performance decay in terms of frames per second when dealing with deformable models, since it becomes necessary to update the acceleration structures to cope with changing geometry, but even under these restrictions, we were able to achieve interactive frame rates.