Research On Realistic Global Illumination Algorithms:From Offline To Real-time

Global illumination is the most difficult topic of computer graphics.Based on the existing methods,this thesis implemented three global illumination algorithms.Those three algorithms implemented in this paper are: offline ray tracing;interactive ray tracing based on Graphics Processing Unit(GPU);real-time global illumination based on voxel cone tracing.The offline ray tracing algorithm calculates the global illumination effect based on Monte Carlo integration method.The diffuse reflection is approximated by the cosine-weighted hemispherical sampling method.And the direct illumination is approximated by solid-angle cone sampling.The offline ray tracing method could achieve unbiased global illumination at a slow rate.The GPU-based interactive ray tracing parallelizes offline ray tracing through the Compute Unified Device Architecture(CUDA)parallel computing interface.A bounding volume hierarchy is built on the GPU to accelerate the intersection tests.Three sampling methods are used to improve the convergence rate.Those three methods are importance sampling,super-sampling anti-aliasing and Russian roulette.A real camera model with aperture is utilized to generate the depth of field effect.Real-time global illumination is achieved based on the voxel cone tracing method.By storing the simplified scene with illumination information in the voxel structure,the indirect illumination effects could be obtained via the voxel cone tracing method.Only dynamic parts of the scene are updated in each frame,which not only supports dynamic light source but also avoids unnecessary calculations on static parts.The voxel structure is a directional hierarchical structure generated by anisotropic filtering,which can be compressed and stored in the mipmapped three-dimensional texture,thus reducing the storage cost.By collecting the outgoing radiance and the occlusion value stored in the voxel structure through the voxel cone tracing method,it is possible to calculate the global illumination effects such as ambient occlusion and soft shadow.Comparing to other related papers,this thesis has better indirect illumination propagation process.This thesis supports dynamic scenes and dynamic illumination than the comparative paper.The experimental results demonstrate that this approach is capable to compute various global illumination effects and has decent rendering efficiency.Moreover,in complex scenes,a real-time frame rate can be achieved(single frame time is less than 33.3 ms).