All-frequency rendering of dynamic, spatially-varying reflectance
All-frequency rendering of dynamic, spatially-varying reflectance
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DOI：
10.1145/1661412.1618479
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发表时间：
2009-12
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影响因子：
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通讯作者：
Jiaping Wang;Peiran Ren;Minmin Gong;John M. Snyder;B. Guo
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文献类型：
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作者：
Jiaping Wang;Peiran Ren;Minmin Gong;John M. Snyder;B. Guo
我们描述了一种在静态场景中实时渲染动态、空间变化的brdf的技术，该场景具有来自环境和点光的全频率阴影。6D SVBRDF用一个通用的微面模型表示，球体瓣符合其4D空间变化正态分布函数（SVNDF）。球面高斯函数（SGs）的和提供了一个具有少量叶的精确近似值。用简单的解析表达式动态拟合参数brdf；采用非线性优化的预处理方法拟合实测brdf。我们的BRDF表示是紧凑的，允许详细的纹理，在产品和旋转下关闭，并支持任意高镜面的反射率。在运行时，表示NDF的SGs被扭曲以使半角矢量与照明方向对齐，并乘以微面阴影和菲涅耳因子。这在每个像素上产生相关的二维视图切片，仍然以SG为基础表示。我们使用基于球面符号距离函数（ssdf）的新的非线性可见性表示来解释宏观尺度阴影。ssdf允许高频可视性的逐像素插值而不会出现重影，并且可以在GPU上有效地乘以BRDF和照明。
We describe a technique for real-time rendering of dynamic, spatially-varying BRDFs in static scenes with all-frequency shadows from environmental and point lights. The 6D SVBRDF is represented with a general microfacet model and spherical lobes fit to its 4D spatially-varying normal distribution function (SVNDF). A sum of spherical Gaussians (SGs) provides an accurate approximation with a small number of lobes. Parametric BRDFs are fit on-the-fly using simple analytic expressions; measured BRDFs are fit as a preprocess using nonlinear optimization. Our BRDF representation is compact, allows detailed textures, is closed under products and rotations, and supports reflectance of arbitrarily high specularity. At run-time, SGs representing the NDF are warped to align the half-angle vector to the lighting direction and multiplied by the microfacet shadowing and Fresnel factors. This yields the relevant 2D view slice on-the-fly at each pixel, still represented in the SG basis. We account for macro-scale shadowing using a new, nonlinear visibility representation based on spherical signed distance functions (SSDFs). SSDFs allow per-pixel interpolation of high-frequency visibility without ghosting and can be multiplied by the BRDF and lighting efficiently on the GPU.