Research On Interactive Global Illumination Rendering With Dynamic Materials

This thesis is about interactive global illumination rendering with dynamic materials. The users can change the materials by interaction if dynamic materials are used. Global illumination rendering with fixed materials can be solved by precomputed radiance transfer(PRT). Researchers turn to global illumination rendering with dynamic materials these years. The algorithms proposed in this thesis allow the users to change the materials while global illumination results are rendered with interactive performance.The algorithms in this thesis are about two kinds of rendering scenes. In the first, the geometry remains unchanged, we use the bidirectional reflectance distribution functions(BRDFs) to represent the dynamic reflection materials, and the scattering, reflection and transparency are not included. In the second, the geometry can be changed by users, the objects are with refractive and scattering materials.For the first kind of rendering scenes, the main contribution of our algorithm is radiance transfer separation for different light paths. The algorithm of PRT used for fixed materials renders with dynamic illuminations in real-time according to the linear relationship between rendering results and illuminations. But the rendering results do not linearly depend on the materials, so PRT can not interactively render with dynamic materials. Even the total radiance to the viewpoint is not linearly dependent on the materials, the radiance transferring along a given light path is linearly dependent on the product of all the reflective materials on the way. So the radiance transfer separation converts the non-linear problem to the sum of a number of linear problems. We precompute the radiance transfers of different light paths independently, which is different from PRT whose precomputation is for the whole radiance transfer. This is the first algorithm of pixel based real-time global illumination rendering with dynamic materials. Our algorithm not only renders global illumination results in real-time with spatial static dynamic materials, which allows the users to change the material of a whole object, but also interactively renders global illumination results with spatial variant dynamic materials, which allows the users to apply different changes to the materials of different parts of an object.We also propose an algorithm of vertex-based interactive global illumination rendering with spatial static dynamic materials. This is the first algorithm allowing the users to change the material, environment lighting and viewpoint simultaneously, and the real-timer performance can be achieved when the environment lighting is fixed. The algorithm includes three contributions: light path separation, precomputed transfer tensors, mirror separation and tensor decomposition of BRDFs. The light path separation reduces the size of the data of the radiance transfer. The precomputed transfer tensor is used to represent, precompute, store and render the radiance transfer. The mirror separation and tensor decomposition of BRDFs are used to achieve fast shading on object surface under dynamic local incident radiance, dynamic material and dynamic viewpoint.For the second kind of rendering scenes, our main contribution is to propose a complete rendering pipeline, which is the first solution of interactive global illumination rendering with dynamic reflective and scattering materials. The inputs of the pipeline are geometry, materials, illumination and viewpoint, so the users can change all of these parameters while global illumination rendering interactively. The whole pipeline is implemented on graphics processing units(GPUs) to achieve interactive performance. There are two very important stages of the pipeline, which are also our contributions: fast voxelization makes the rendering which dynamic geometry possible, the adaptive non-linear photon-mapping is critical to the interactive performance of our pipeline.The algorithms in this thesis have many applications, such as games and computer aided design. Our rendering pipeline for refractive and scattering materials can be also used as interactive visualization algorithm for mesh deformation, interactive modeling and fluid physical simulation.