基于预计算的高精度可见性及压缩编码

Precomputed High-Precision Visibility and Compression Encoding

可见性表示三维模型表面之间的遮挡关系,使得渲染画面具备立体感。由于可见性是一个定义在半球面上的方向分布函数,难以实时计算。因此,在实际应用中,可见性通常从光照计算中剥离出,最后使用近似可见性的技术(如环境遮蔽)来弥补渲染画面的立体感。但在一些情况下需要更加精准的可见性。基于预计算的思想,借助球谐函数作为球面基函数,将可见性分布函数转化为对n个球面基函数系数的存储,并进一步压缩为可见性圆锥,实现一种高精度、低存储量的可见性。

Visibility represents occlusions between surfaces of three-dimensional models,which makes the render image with great stereoscopic sense.Visibility is a direction function which defines on the hemisphere surface,thus it is difficult to calculate in real-time.Therefore,visibility is usually separated from the lighting calculation,and finally,the technology of approximate visibility(such as ambient occlu sion)is used to make up for the stereoscopic sense of the rendered image.Based on the idea of precomputed,with the spherical harmonic function as the spherical basis function,the visibility distribution function is transformed into the storage of the coefficients of n spherical basis functions,and further compressed into a visibility cone,thus achieving a high precision and low memory visibility.