针对带有微结构表面的几何模型全局光照计算复杂、难以达到实时性要求的问题,提出一种基于高度梯度图分析的全局光照实时绘制方法.首先,定义微结构高度梯度图,并据此构建可见点的局部最高点集合.其次,给出面向微结构表面对象实时绘制的全局光照计算模型,将光照计算近似分解为环境光入射、光源直接光照和一次交互漫反射这3 种分量的计算.在环境光计算过程中,提出一种自适应环境光遮挡计算,借助局部最高点集合计算遮挡角.在直接光照中,给出一种微结构阴影的修正方法,搜索入射光方向的最近局部最高点剖面;通过比较剖面内光线投影与局部最高点的遮挡角,近似确定由微结构造成的阴影区域.最后,根据可见点的局部最高点集合确定一次交互漫反射的采样范围,进行渗色处理.整个全局光照计算方法在图像空间完成,较好地利用了延迟着色的思想和GPU 并行计算的特点.算法可以在使用低精度几何模型时表现出带有微结构表面的高精度模型的全局光照效果,且适用于动态场景和可变形物体的全局光照计算.

Rendering global illumination for objects with mesostructure surfaces is a time-consuming task and cannot presently be applied to interactive graphics. This paper presents a real-time rendering method, based on a mesostructure height gradient map (MHGM), to exhibit lighting effects on meso-scale detail level in dynamic environments. This paper approximates global illumination by using a lighting model that includes specific characteristics: Incident ambient light, direct light, and a single bounce indirect light. In order to compute these three components in real time, this paper introduces the MHGM to create local apex sets, with which an adaptivemethod for calculating ambient occlusion is proposed. In direct lighting, the nearest local apex profile of the incident rays is to be found and presented as a mesostructure shadow algorithm, which can generate the shadow of meso-scale details. The color of the points enclosed by the local apexes is also sampled to estimate a single bounce indirect light. This approach runs entirely on the graphics hardware and uses deferred shading and the graphicspipeline to accelerate computation. High quality results, which can render meso-scale details with global illumination even for low-resolution geometric models, are achieved. Moreover, this approach fully supports dynamic scenes and deformable objects.

国家自然科学基金(60842001); 北京市科技新星计划(2009B09); 澳门科学技术发展基金(043/2009/A2)