Research Of Real-Time Global Illumination Rendering

As an important component of computer graphics,photorealistic rendering technology is dedicated to simulate the real world using computers,and render the three dimensional scenes into very real images.The realistic of images that the computer rendered is to a large extent by the lighting models that used.Compared to the Local Illumination,the Global Illumination rendering technology includes not only the effect of direct light from the light source,but also needs to consider the factors of the indirect light effects in the scene,such as reflection and refraction,thus its' rendering image is much better the Local Illumination.The technology of Global Illumination which can achieve realistic lighting effects,has attracted many domestic and foreign scholars' attention and study.As an important global illumination rendering method,ray tracing,is in full accordance with the principles of optics for lighting and rendering process,thus has more superior reality comparing to other global illumination algorithms theoretically.However,the amount of light that the traditional ray tracing algorithm needs to process and compute is too large,making ray tracing that fully simulate global illumination difficult to apply to virtual reality,games and other real-time rendering fields.The acceleration structure of ray tracing can effectively reduce the computing cost of light-objects intersecting,which is the performance bottleneck of ray tracing,thereby could enhancing the performance.The accelerating structures include space acceleration structure represented by the KD tree and hierarchical acceleration structure,represented by BVH(Bounding Volume Hierarchy),which is more suitable in dynamic scenes,and easier to be implemented on the GPU.The research goal of this thesis is to maintain a high rendering quality in the premise,through the research and improvement of the existing ray tracing acceleration structure and the high performance of the NVIDIA OptiX ray tracing engine on the GPU,to achieve the real-time performance improvement of global illumination rendering.The main work and achievements of this thesis are as below:Research recent BVH acceleration structures of the representative improved methods: LBVH and SBVH.Combined LBVH's fast GPU building performance with SBVH's idea of splitting triangles,and then optimize the BVH's structure to give an improved BVH method,which contains the advantages of both methods.This improved method can build a BVH with the speed close to LBVH,while achieve about 90% of the SBVH's traversal performance in dynamic scenes of medium and small scale,which can offer better performance.Designed a programmable global illumination rendering pipeline based on the OptiX ray tracing engine,with which other global illumination methods based on ray tracing algorithm can be implemented;implement a global illumination renderer based on ray tracing,which supports a variety of materials,experiment results show that its rendering quality is close to the CPU-based Mitsuba renderer and its rendering speed is about 7 times,and it can achieve real-time or interactive level in medium and small-scale scenes.