Accurate appearance preserving prefiltering for rendering displacement-mapped surfaces
Accurate appearance preserving prefiltering for rendering displacement-mapped surfaces
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DOI：
10.1145/3306346.3322936
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发表时间：
2019-07
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影响因子：
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通讯作者：
Lifan Wu;Shuang Zhao;Ling-Qi Yan;R. Ramamoorthi
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文献类型：
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作者：
Lifan Wu;Shuang Zhao;Ling-Qi Yan;R. Ramamoorthi
预滤波位移映射表面的反射率，同时保持其整体外观是具有挑战性的，因为平滑位移映射会导致照明效果的复杂变化，如遮蔽和互反射。本文提出了一种将位移图和brdf联合预滤波并构建降分辨率svbrdf的新方法。这些svbrdf通过捕捉阴影掩蔽和互反射效果来保持输入模型的外观。为了有效地表达我们的保持外观的svbrdf，我们利用了一种新的表示方法，该方法涉及空间变化的ndf和一种新的缩放函数，该函数可以准确捕获阴影、掩蔽和互反射效应的微观变化。此外，我们证明了6D尺度函数可以分解为表面位置的2D函数和方向的4D函数。通过利用这些函数的平滑性，我们开发了一种简单有效的不需要计算全尺度函数的分解方法。生成的函数可以以低分辨率表示（例如，空间函数为42，角函数为154），导致最小的额外存储。我们的方法可以很好地推广到高斯曲面以外的不同几何类型。使用我们的方法在不同尺度上预过滤的模型可以组合成mipmaps，从而实现精确和抗锯齿的细节级（LoD）渲染。
Prefiltering the reflectance of a displacement-mapped surface while preserving its overall appearance is challenging, as smoothing a displacement map causes complex changes of illumination effects such as shadowing-masking and interreflection. In this paper, we introduce a new method that prefilters displacement maps and BRDFs jointly and constructs SVBRDFs at reduced resolutions. These SVBRDFs preserve the appearance of the input models by capturing both shadowing-masking and interreflection effects. To express our appearance-preserving SVBRDFs efficiently, we leverage a new representation that involves spatially varying NDFs and a novel scaling function that accurately captures micro-scale changes of shadowing, masking, and interreflection effects. Further, we show that the 6D scaling function can be factorized into a 2D function of surface location and a 4D function of direction. By exploiting the smoothness of these functions, we develop a simple and efficient factorization method that does not require computing the full scaling function. The resulting functions can be represented at low resolutions (e.g., 42 for the spatial function and 154 for the angular function), leading to minimal additional storage. Our method generalizes well to different types of geometries beyond Gaussian surfaces. Models prefiltered using our approach at different scales can be combined to form mipmaps, allowing accurate and anti-aliased level-of-detail (LoD) rendering.