Efficient Schemes For Ray Tracing Parametric Surfaces

• Main Authors: Shyue-Wu Wang, 王學武
• Other Authors: Ruei-Chuan Chang
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/86983224695761357805

博士 === 國立交通大學 === 資訊科學系 === 89 === Ray tracing is one of the most important rendering techniques in computer graphics because of its ability in producing photo realistic images. However, ray tracing is a time-consuming process especially for parametric surfaces, such as B-spline and Bezier surfaces. In this thesis, we propose an enhanced rendering framework for ray tracing parametric surfaces. The key point of our proposed rendering framework is to improve the performance of the following tasks: calculating the ray-surface intersection points and locating of the closest intersection points. To locate the closest intersection points efficiently, we introduce an obstruction detection technique to verify whether an intersection point is the closest one. Besides, a similar approach is also proposed to improve the performance in tracing secondary rays. Based on this rendering framework, we will discuss several methods for improving the performance of ray tracing parametric surfaces. The first algorithm is based on the combination of two most commonly used approaches: numerical methods and subdivision methods. The property of Newton's method with ray coherence is used to find the ray-surface intersection points. To overcome the problem while using Newton's method with ray coherence, we use the obstruction detection technique to verify whether an intersection point found by Newton's method is the closest one. When Newton's method fails to converge, we use Bezier clipping as the substitution to find the intersection points. Experimental results indicate that our algorithm do improve the performance of Bezier clipping by 50% on tracing primary rays. Furthermore, the improved approach on tracing secondary rays introduces a 20% to 50% reduction in total rendering time. The second issue considered is to improve both numerical methods and subdivision methods with the enhanced rendering framework. Since both numerical and subdivision methods have their own rendering process, it is difficult to create a general improvement scheme. Individual schemes are proposed for numerical and subdivision methods to enhance their performance. Two algorithms, a subdivision method and a numerical method, are modified and implemented. Experimental results indicate that the improved algorithms can reduce total rendering time by 16% to 40%.