Interactive Photorealistic Rendering In Dynamic Scenes

Photorealistic rendering is one of main fields in rendering. The goal of it is to accurately simulate light transport and various lighting effects. It mainly focuses on reproducing scenes in real life and is widely used in applications that require high image quality, like movie production. Photorealistic rendering requires accurate models for various elements in the scene including light source, geometry, material and media. It also simulates the complex transport of light in the scene therefore is computationally expensive, which has been limiting it to off-line applications for a long time. In the recent years, along with rapid advances in graphics hardware and the growing needs from users, photorealistic rendering is gradually integrated into some interactive and real-time applications, including games and virtual reality systems.The core of photorealistic rendering algorithms is to solve the rendering equation. There are two bottlenecks in computing this equation. The first one is visibility evaluation that determines whether two points in the scene are visible to each other. This problem is more important in dy-namic scene in which case the relative position of objects are changing with time and cannot be accelerated using precomputation. The second bottleneck is to calculate the integration in the ren-dering equation. According to the rendering equation, the outgoing radiance at each shading point depends on an integration over the hemisphere which involves BRDF, visibility and incident light at each incoming direction and can be very complex.In this dissertation, we will focus on the above two bottlenecks and present new algorithms to accelerate their computation. We present different solutions to the different forms of the rendering equation when applied to various photorealistic effects including shadows, interreflections and all-frequency relighting and boost the performance to interactive or even real-time. Our contribution is as follows:·Propose a fast algorithm for rendering shadows with sub-pixel accuracy. Shadow is one of the important effects in photorealistic rendering and also one of the visibility problems. Generating shadows with sub-pixel accuracy requires a large amount of visibility evaluation, which is proportional to the number of pixels, the number of triangles and the sample rate. We propose three methods named facet approximation, shadow silhouette maps and software rasterization algorithm to reduce all these variables, thus avoiding unnecessary shadow tests. Our algorithm has high parallelism and can be implemented completely on GPU with real-time performance.·Propose an algorithm for computing low-frequency interreflections in dynamic scenes. The rendering equation can have different forms when applied to different photorealistic effects. We start from its corresponding form for interreflection in dynamic scenes and extract the invariant within it, which is the linear relationship between incident light on the object and the reflected light in the space around the object. The invariant is precomputed and stored in a data structure called radiance transfer field. During rendering, the rendering equation is simplified to a multiplication between a transport matrix stored in the radiance transfer field and a vector representing the incident light. Therefore, interrefection effect can be imple-mented with very little cost. We employ the clustered principal component analysis method to compress the radiance transfer field. Two caching mechanisms are also presented to fur-ther reduce computing cost of the rendering equation.·Propose a computing framework for the rendering equation using double product integral and propose an analytic solution to it. By moving the visibility term from the integrand to the integration domain, we convert the rendering equation to a double product form, there-fore avoid the computation of triple product, which is usually a bottleneck in precomputed radiance transfer algorithms. After locally approximating the product of light and BRDF using Legendre polynomials, the solution of the integration is given in analytic form. We also propose a hierarchical boundary extraction method to reconstruct the visibility bound-ary with the lowest error. Our method can render all-frequency lighting effects with real-time frame rate. Two adaptive visibility sampling methods and a parallel spherical distance trans-form method are also presented to extend the analytic double product integral framework to dynamic scenes with interactive performance.