辐射度场景中双向纹理函数表面的绘制

Rendering Surfaces with Bidirectional Texture Function by Radiosity Method

双向纹理函数(BTF)表面一般采用点采样数据来定义表面的光照属性,因而这类表面很难运用基于面片分割的辐射度方法进行绘制,提出一种将辐射度算法扩展到包括BTF表面场景的有效方法.对表面的BTF样本区域首先进行像素聚类,再在各个像素类内对视线采样方向做进一步自适应的聚类,在各个视线类内像素分别拟合一个低频光照函数,并求它们在各个视线类内光照细节的高频光照函数.低频光照函数作为该表面区域的平均反射属性参与辐射度计算,生成场景的整体光照效果;然后利用计算的辐射度值和高频光照函数重建该表面区域的BTF材质细节.文中方法不仅取得了较高的压缩效率,而且在BTF材质表面产生了辉映等全局光照效果.最后利用硬件实现了视点快速改变时的场景绘制.

Surfaces with bidirectional texture function （BTF） is rarely rendered by radiosity method, because their materials are normally defined by point based sampling, which does not adapt to the conventional patch-based process of radiosity approach. An efficient algorithm for integrating BTF surfaces into the framework of radiosity is presented. For a BTF sample set, a clustering process is first applied to all pixels according to their intensity divergences. Then in each pixel cluster, all the viewing directions with similar shading effects are clustered further. Each refined cluster is fitted by a low frequency illumination model, and the high frequency deviation of the estimated shading from the real intensity at each pixel within the cluster regarding each viewing direction is calculated. The low frequency model is assigned to the local surface region as its average reflectance for radiosity calculation. The high frequency model is employed for building the detail on the surface. Our approach achieves high compression rate and generates interrefection shading effects on the BTF surfaces. GPU is also used to speed up the rendering performance.