【作者】 陈大炜；

【导师】 王乘；

【作者基本信息】 华中科技大学 ， 系统分析与集成， 2006， 博士

【摘要】 虚拟环境生成是虚拟现实应用的基础和保障,实时性和真实感是虚拟环境生成的两个基本要求。即使在计算机硬件处理能力,特别是图形硬件性能突飞猛进的今天,虚拟环境的真实感和实时性要求之间也必须采取某种程度的折衷。在虚拟环境生成领域,保留模式下的场景图系统已经成为事实上的主流解决方案。本文的主要研究目的就是面向场景图系统在保证实时性的前提条件下,尽可能的提高虚拟环境生成的真实感。本文主要研究内容包括虚拟环境生成中的光照真实感和运动真实感两个关键问题:在光照真实感方面,本文又将其分为两个子问题来解决,一是研究如何在场景图系统中利用基于可编程图形处理器的像素级着色处理技术进行实时渲染以获得更好的视觉外观,二是研究如何在保留模式下的虚拟环境中实时的生成高质量的动态阴影效果。对于虚拟环境的运动真实感方面的研究,主要解决如何面向场景图系统针对虚拟环境中刚体对象的动力学建模问题,从而保证虚拟环境中的运动一致性。本文的主要贡献包括以下几个方面:1)面向通用场景图系统,引入了一种新的支持高级着色语言的可编程节点类型,基于可编程图形硬件设计并实现了一种实时像素级光照方法,弥补了仅能支持传统顶点光照的通用场景图系统的不足,在很大程度上改善了虚拟环境中模型对象光滑表面的视觉外观。2)利用本文提出的基于图形处理器的实时像素级光照技术,通过对标准局部光照模型的改进,在场景图系统中实现了一种增强的基于法线贴图的实时凸凹映射方法,从而极大的改善了通用场景图系统生成的虚拟环境中模型对象粗糙表面的表现能力。3)对实时阴影生成算法,特别是基于图像空间的阴影图算法进行了深入研究,针对虚拟环境动态阴影实时生成的实际问题,通过对光源空间透视阴影图算法的改进和优化,面向场景图系统提出并实现了一套完整的实时阴影生成算法,同时充分利用本文实现的场景图中的可编程节点功能,在很大程度上改善了虚拟环境生成中的光照真实感问题。4)借鉴场景图的思想,对基于场景图系统的刚体运动建模方法进行了研究,提出了面向刚体碰撞处理的物理空间场景图概念。面向通用场景图系统提出并设计了一个实时刚体动力学仿真模拟框架,最后针对通用场景图系统给出了基于开源动力学引擎的模块化实现,解决了虚拟场景中的刚体动力学模拟问题,对虚拟环境的运动真实感进行了有益的探索。更多还原

【Abstract】 Virtual Environment generation is the essential element for the application of virtual reality, which has two basic demands, the quality of real time and reality. Even though the rapid enhancements have been made for the performance of the graphic hardware, some compromise must be made between the demanding for the real time and reality of virtual environment. In the field of Virtual Environment generation, scene graph system in the retained mode has actually become the leading scheme. The main research purpose of this thesis is in the precondition of guaranteeing the real time simulation, improving the quality of reality of the virtual environment as much as possible based on scene graph system.The main contents of this thesis include the research on illumination reality and the motion reality, which are the key issues of Virtual Environment generation. To solve the former, this thesis divides it into two sub-problems, one of which focuses on the research of how to get the better vision appearance in scene graph system by using the per-pixel rendering technique based on the programmable graphics processor to make real-time rendering, and the other of which concerns the research of how to creating the real-time high-quality dynamic shadow effect in virtual environment. To solve the latter, the motion reality of virtual environment, this thesis mainly discusses the problem of how to make the rigid body dynamics modeling in virtual environment for scene graph system, which ensures the consistency of the motion in the virtual environment.The important innovation of this thesis includes:1) A new type of programmable shader node for general scene graph system is put forward and a real-time per-pixel lighting method based on the design of the programmable graphics hardware is implemented, which makes up the shortage of scene graph system for the traditional per-vertex lighting, then improves the appearance of the slippery surfaces in the virtual environment very much.2) By using the per-pixel lighting technique put forward in this thesis and improving the standard local illumination mode, an enhanced real-time bump mapping method based on the normal map is realized in scene graph system, which improves the expression for the coarse surfaces in the virtual environment based on general scene graph system.3) Careful research has been done for the real-time shadow algorithms, especially for the shadow algorithms of image space. And aiming at the real problems of real-time dynamic shadow creating in virtual environment, a set of integrated real-time shadow creating method for scene graph system is put forward and realized, by improving and optimizing the light space perspective shadow algorithm, which may be applied with the per-pixel lighting technique and can improve the quality of lighting reality very much.4) Inspired by the scene graph technology, the research on the rigid body dynamics modeling for general scene graph system is done. A real-time rigid body dynamics simulation framework for general scene graph system is put forward and realized in modules using open dynamics engine, which solves the simulation problems of rigid body in virtual environment based on scene graph system.更多还原