QuickWalk:一个大规模场景交互漫游系统

随着三维扫描与建模技术的飞速发展,三维场景的数据量急剧增大,无法一次性载入内存,而且难以进行交互绘制.研究开发了一个大规模外存场景的交互漫游系统QuickWalk,该系统集成了视点相关的层次细节技术、可见性剔除和场景数据的内外存调度,能够有效地减少运行时刻的内存需要,使CPU、GPU和I/O三者的效率得到充分发挥.实验表明,在保证场景绘制质量的前提下,该系统能够在目前普通的PC上实现大规模外存场景的实时显示和交互操纵.     

大规模复杂场景的可见性问题研究

大规模复杂场景的快速绘制技术是虚拟现实、实时仿真以及三维交互设计等许多重要应用的底层支撑技术,也是诸多研究领域面临的一个基本问题．作为其中一个技术解决手段,可见性问题在近年来得到了高度重视并取得了一系列研究成果．通过对相关可见性算法进行分析与总结,阐述了可见性问题的研究内容,提出了方法的优劣判别标准,给出了可见性判断算法所应包含的基本组成部分和步骤,最后指出未来仍然需要重点研究的若干关键问题．     

一种高度并行的多任务并行绘制系统结构

随着计算机图形技术的实用化，需要构造更逼真、更精细的三维复杂场景，其数据规模日益膨胀，加上对场景的实时交互的要求也越来越高，人们对多屏幕高分辨率显示的需求与日俱增，迫切需要一种针对大规模复杂场景的多任务并行图形绘制系统。本文介绍了一种适用于大规模复杂场景的高度并行的多任务多屏幕并行图形绘制系统的体系结构，支持图形任务的并行化处理和多屏幕显示。该系统结构将几何计算任务与图形绘制任务相分离，分剐进行并行化处理，在计算节点按绘制对象类型对任务进行分类以便于并行计算和任务分配，在绘制节点对各个小块屏幕图形进行并行合成。实验测试结果表明，该系统结构对多任务具有较好的并行效率和可扩展性，能够充分利用系统的并行计算资源，达到较好的绘制效果。     

大规模外存场景的交互绘制

在场景分割的基础上,提出一种连续分层层次细节模型组织场景,并对视点空间进行划分,为每个视点单元计算恰好满足单元内任意视点屏幕像素误差的场景图节点列表,称为cell-front;然后利用cell-front对外存模型的存储进行重新设计.在绘制时采用多线程技术,绘制线程对当前cell-front进行可见性剔除和视点相关的选择绘制;预取线程采用一种基于视点单元的预取策略,利用视点单元之间cell-front的变化控制预取数据的调度.该算法能够在保证场景绘制质量的前提下,在普通的PC机上实现大规模外存场景的实时交互显示.     

论实时绘制大规模场景的各种技术

近年来实时图形设计已经成为计算机图形学的研究重点.本文详细地为大家介绍开发一个实时绘制大规模三维场景的程序系统所用到的各种技术.     

基于体绘制的动态云场景模拟

为了实现动态云场景的创建与绘制,文中提出一种基于体绘制的三维云模拟算法。算法用Perlin噪声干扰椭球模型,得到云场景区域内体素颜色的基本数据,然后对体素颜色进行软化模糊和添加阴影处理,建立绘制区域的云数据模型;同时通过ray casting对绘制区域进行体数据采样渲染,模拟出三维云的效果。仿真实验结果表明：该算法模拟出的云场景可让云形状颜色位置动态改变,也可让视点穿过云层,具有动态和交互效果,是一种可行的动态云场景模拟算法。     

基于多线程并行的大规模场景交互漫游研究

针对大规模三维场景的交互漫游,提出了一种基于多线程并行调度解决方案,并给出了相应的交互漫游算法.该方法使用离散层次细节技术结合视点相关的动态连续层次细节选择和过渡的批LOD技术.在预处理阶段,对大规模场景进行分层分块处理;在实时漫游阶段,采用多线程并行技术:绘制线程利用四又树层次进行可见性剔除和视点相关简化获取当前可绘地形,并将其提交给GPU进行绘制.预取线程通过预测视点的位置,从外存预取相关的几何数据并调入内存.将该方法应用于具体实例,取得了良好效果,证明了该并行方法的有效性.     

基于状态转换优化策略的多属性对象绘制方法

复杂场景的高效绘制是计算机图形学研究中的一个重要内容,目前的研究大多集中在对场景组织及可见性裁剪等降低场景几何复杂度的加速方法上,而针对场景中对象的多属性管理及绘制优化方法的研究较少.由于复杂场景中的对象除了基本几何信息外还包括光照、材质、纹理等多种绘制属性,这些属性的频繁切换将对绘制效率产生极大的影响,进而降低绘制的实时性.为此,提出一种基于状态转换优化策略的多属性对象绘制方法,通过定义绘制状态对场景中对象的属性进行管理,并将绘制状态的转换关系表示为带权有向图,进而利用最优化算法找到绘制状态转换的优化序列.实验结果表明,对于具有多属性对象的复杂场景,该方法能够有效地降低状态转换的开销,提高场景的实时绘制效率.     

基于场景结合的大规模动态群体可见性计算方法

动态场景的可见性计算对于大规模场景的实时渲染具有重要意义,其中运动中的大规模群体更给可见性计算带来了很大的开销.针对大规模动态群体在建筑物场景内部运动的情况,提出一种与场景结合的动态群体可见性计算方法.在预处理时,根据个体在不同仿真时刻的位置,将其绑定到相应的场景节点中;在实时绘制时,结合场景的可见性判断结果对动态群体中的个体进行可见性判断.实验结果表明,该方法能高效地剔除动态群体中的不可见个体,使大规模动态场景的实时绘制效率得到明显提高.     

森林场景的钢笔风格化实时绘制技术*

在大型复杂场景绘制关键技术研究项目中,通过把复杂场景绘制与调度技术,如Slicing、MMI、层次图像缓存和基本布告板等大场景实时加速绘制技术的多层次绘制方法,融合到非真实感绘制技术中,以提高系统面对复杂场景的实时绘制能力。最后实现了对森林等大型场景的钢笔画绘制,借助非真实感绘制技术中基于图像空间的生成方法,利用各种不同大小及形状的笔画实现了艺术化森林场景实时交互绘制。提出了植物多层次钢笔风格化渲染算法。     

Separating semantics from rendering: a scene graph based architecture for graphics applications

A large number of rendering and graphics applications developed in research and industry are based on scene graphs. Traditionally, scene graphs encapsulate the hierarchical structure of a complete 3D scene, and combine both semantic and rendering aspects. In this paper, we propose a clean separation of the semantic and rendering parts of the scene graph. This leads to a generally applicable architecture for graphics applications that is loosely based on the well-known Model-View-Controller (MVC) design pattern for separating the user interface and computation parts of an application. We explore the benefits of this new design for various rendering and modeling tasks, such as rendering dynamic scenes, out-of-core rendering of large scenes, generation of geometry for trees and vegetation, and multi-view rendering. Finally, we show some of the implementation details that have been solved in the process of using this software architecture in a large framework for rapid development of visualization and rendering applications.     

Time‐critical rendering algorithm with incorporation of LoD,visibility culling and object impostor

Given enough CPU time, present graphics technology can render near‐photorealistic images. However, for real‐time graphics applications such as virtual reality systems, developers must make explicit programming decisions, trading off rendering quality for interactive update rates. In this papar we present a new algorithm for rendering complex 3D models at near‐interactive rates that can be used in virtual environments composed of static or dynamic scenes. The algorithm integretes the techniques of level of details (LoD), visibility computation and object impostor. The method is more suitable for very dynamic scenes with high depth complexity. We introduce a new criterion to identify the occluder and the occludee: the object that can be replaced by its LoD model and the one that can be replaced by its impostor. The efficiency of our algorithm is then illustrated by experimental results. Copyright © 2003 John Wiley & Sons, Ltd.     

实时三维图形平台BH_GRAPH

BH_GRAPH是一个面向视景仿真类应用系统开发人员、支持实时三维图形开发与运行的基础软件平台．它提供可扩展的软件体系结构、标准化的场景管理机制、高效率的场景处理方法、方便易用的应用程序接口,为三维图形应用系统的快速开发、高效运行提供完整的技术支撑．BH_GRAPH主要由三维视景绘制引擎、三维对象建模工具、三维场景布置工具以及一系列关键技术构成．概要介绍了BH—GRAPH各主要组成部分的软件结构、基本功能和技术特点．     

复杂环境光源下的动态场景实时绘制算法综述

在交互式图形应用(如互动游戏)中,复杂环境光的使用越来越普遍,并提供了比传统虚拟光源更高的真实感.对复杂环境光下的动态场景实时绘制算法进行综述,通过回顾这些算法的基本思想、假设、局限性和可使用范围,来对它们的特性进行描述和比较.特别地,文中还试图通过分析相关研究的内在联系来指出该领域未来的主要研究方向.     

Faster isosurface ray tracing using implicit KD-trees

The visualization of high-quality isosurfaces at interactive rates is an important tool in many simulation and visualization applications. Today, isosurfaces are most often visualized by extracting a polygonal approximation that is then rendered via graphics hardware or by using a special variant of preintegrated volume rendering. However, these approaches have a number of limitations in terms of the quality of the isosurface, lack of performance for complex data sets, or supported shading models. An alternative isosurface rendering method that does not suffer from these limitations is to directly ray trace the isosurface. However, this approach has been much too slow for interactive applications unless massively parallel shared-memory supercomputers have been used. In this paper, we implement interactive isosurface ray tracing on commodity desktop PCs by building on recent advances in real-time ray tracing of polygonal scenes and using those to improve isosurface ray tracing performance as well. The high performance and scalability of our approach will be demonstrated with several practical examples, including the visualization of highly complex isosurface data sets, the interactive rendering of hybrid polygonal/isosurface scenes, including high-quality ray traced shading effects, and even interactive global illumination on isosurfaces.     

一种场景内容分布的交互式渲染系统

近年来,三维虚拟场景的规模和复杂程度不断提高,受到硬件的限制,一些应用 中的超大规模场景(如建筑群,城市等)很难在单机上进行渲染或满足可交互的需求。针对该问 题,提出了一种分布式渲染框架,将大规模场景在内容上进行划分,得到单一节点可渲染的子 场景。这些子场景被分布到集群中不同的渲染节点进行处理,其渲染结果根据深度信息进行合 成得到整个场景的最终渲染结果。为了降低交互响应时间,需对子场景的渲染结果进行压缩传 输。实验充分验证了提出的分布式渲染系统能够高效处理超大规模场景的渲染和交互,并且具 有良好的可扩展性,能够满足很多领域中对大规模场景交互式渲染的需求。     

Efficient and Accurate Sound Propagation Using Adaptive Rectangular Decomposition

Accurate sound rendering can add significant realism to complement visual display in interactive applications, as well as facilitate acoustic predictions for many engineering applications, like accurate acoustic analysis for architectural design (Monks et al., 2000). Numerical simulation can provide this realism most naturally by modeling the underlying physics of wave propagation. However, wave simulation has traditionally posed a tough computational challenge. In this paper, we present a technique which relies on an adaptive rectangular decomposition of 3D scenes to enable efficient and accurate simulation of sound propagation in complex virtual environments. It exploits the known analytical solution of the wave equation in rectangular domains, and utilizes an efficient implementation of the discrete cosine transform on graphics processors (GPU) to achieve at least a 100-fold performance gain compared to a standard finite-difference time-domain (FDTD) implementation with comparable accuracy, while also being 10-fold more memory efficient. Consequently, we are able to perform accurate numerical acoustic simulation on large, complex scenes in the kilohertz range. To the best of our knowledge, it was not previously possible to perform such simulations on a desktop computer. Our work thus enables acoustic analysis on large scenes and auditory display for complex virtual environments on commodity hardware.     

HTML5-based system for interoperable 3D digital home applications

Digital home application market shifts just about every month. This means risk for developers struggling to adapt their applications to several platforms and marketplaces while changing how people experience and use their TVs, smartphones and tablets. New ubiquitous and context-aware experiences through interactive 3D applications on these devices engage users to interact with virtual applications with complex 3D scenes. Interactive 3D applications are boosted by emerging standards such as HTML5 and WebGL removing limitations, and transforming the Web into a real application framework to tackle interoperability over the heterogeneous digital home platforms. Developers can apply their knowledge of web-based solutions to design digital home applications, removing learning curve barriers related to platform-specific APIs. However, constraints to render complex 3D environments are still present especially in home media devices. This paper provides a state-of-the-art survey of current capabilities and limitations of the digital home devices and describes a latency-driven system design based on hybrid remote and local rendering architecture, enhancing the interactive experience of 3D graphics on these thin devices. It supports interactive navigation of high complexity 3D scenes while provides an interoperable solution that can be deployed over the wide digital home device landscape.