Font Size: a A A

Geometry-based Anti-aliasing In Real-time Rendering

Posted on:2016-10-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:W J DuFull Text:PDF
GTID:1108330470467841Subject:Computer Science and Technology
Abstract/Summary:PDF Full Text Request
Aliasing is a signal distortion phenomenon caused by discrete sampling, storing and representation of continuous information. Anti-aliasing is one of fundamental prob-lems in computer graphics research. Anti-aliasing can effectively reconstruct geometry, texture, or motion details to improve the qualities of synthesized images and animations, and can provide better visual experiences to users. Therefore, anti-aliasing is always an important research topic, which is widely applied to computer game, computer anima-tion, virtual reality and film post-production.Recently, deferred shading becomes a prevalent technique in real-time rendering with the increasing demands of rendering quality and performance in various graphical applications. However, the traditional screen-space anti-aliasing algorithms are not com-patible with the deferred shading techniques, many post-processing anti-aliasing algo-rithms were proposed and became prevalent. Unlike the traditional anti-aliasing method-s relying heavily on the original primitives information, the post-processing algorithms achieve anti-aliasing with the rasterized shading or geometry information of the scene. The challenges in the post-processing anti-aliasing are how to efficiently store and uti-lize the geometry buffer information to generate faithful anti-aliasing results similar to what super-sampling anti-aliasing does. As an important component of realistic render-ing in computer graphics, shadows can reflect the geometry shapes of the objects and their relative positions in the scene. In real-time rendering, shadow mapping algorithm is widely used due to its simplicity and efficiency. However, shadow mapping also suf-fers from the aliasing problems because of the discrete storage of the depth information of the scene. How to generate anti-aliased shadows efficiently is a challenge in shadow mapping algorithms. In this thesis, the aliasing problems in deferred shading and shadow mapping algorithms in real-time rendering are carefully analyzed and studied, and some novel geometry-based solutions are introduced as follow:We first present a sub-pixel anti-aliasing algorithm via triangle-based geometry re-construction for deferred shading. As the geometric evidences of sub-pixel ant-aliasing, the spatial relationship between the coverage triangle of screen pixel and its neighbor-ing sub-pixels is retrieved and stored in a screen-resolution bitmask. Thus the memory requirements of the algorithm are greatly reduced, and the faithful anti-aliasing filtering of sub-pixel can be achieved. Morphological anti-aliasing method is also incorporated into the algorithm as a complement for processing high-frequency geometries. The pro-posed algorithm has good compatibility and scalability, and can achieve high quality anti-aliasing via compact storage of geometry buffer. A unified post-processing anti-aliasing algorithm to deal with both geometric and shading aliasings is proposed. The proposed algorithm can achieve high-quality geomet-ric feature anti-aliasing with sub-pixel-level geometric information, as well as texture filtering using a morphological algorithm and the shading information. To remedy the unsmooth transition between screen pixels caused by the combination of the two type of anti-aliasing algorithms, a re-projection anti-aliasing algorithm is incorporated into the screen space anti-aliasing filter. In this way, the temporal aliasing, appearing as flicker-ing phenomenon in animated scenes, can be greatly alleviated. Compared with previous approach which deals with one type of aliasing individually, the proposed approach can achieve various type of anti-aliasings in a unified framework.To process aliasing in shadow mapping algorithm, a geometric shadow mapping algorithm based on triangle geometry reconstruction is proposed. In this algorithm, the original triangles of the scene is stored in the shadow map to represent the occluder-s. Thus both aliasing and depth bias issue problems can be alleviated due to accurate depth reconstruction. A GPU-based geometry buffer compression method is also pro-posed to reduce the storage redundancy of triangles. Packet-based shadow evaluation is employed to further reduce the total memory fetch overhead. To remedy artifacts in the inconsistent pixels, the depth value of occluder is estimated via linear extrapolation of neighbor depthes. As a geometry-based solution, the proposed algorithm can generate high-quality shadows efficiently.From the point of view of discrete signal reconstruction, an efficient linear shad-ow mapping algorithm is proposed. The algorithm adopts linear reconstruction as the pre-filtering of point sampled shadow map. For the sake of the smooth shadow silhou-ette, a silhouette reconstruction method is integrated into the algorithm. Compared with the conventional shadow mapping algorithm, the proposed algorithm has similar per-formance, while can generate anti-aliased shadow. The algorithm can also incorporate with any uniform point sample based shadow mapping algorithm, e.g., warping, fitting, z-partitioning and adaptive partitioning shadow mappings, and can improve the shadow quality or performance for these anti-aliasing shadow mapping algorithms.
Keywords/Search Tags:anti-aliasing, deferred shading, shadow mapping, triangle-based geometry, linear shadow maps
PDF Full Text Request
Related items