microfacet density ρ exp(20) exp(35) ∞ Figure 1: Left: Sponza scene with sparkling fabrics and stones is rendered on an NVIDIA GeForce RTX 2080 (3.0 ms/frame). Right: A sparkling plane perpendicular to the camera with specular microfacet density increasing from left to right. Top right: our physically based BRDF (2.5 ms/frame) converges to Cook and Torrance's BRDF (0.4 ms/frame), which assumes an infinite number of microfacets. Bottom right: the state-of-the-art method [ZK16] (1.3 ms/frame) is not physically based and does not converge to the BRDF of Cook and Torrance.
Complex specular microstructures found in glittery, scratched or brushed metal materials exhibit high frequency variations in reflected light intensity. These variations are important for the human eye and give materials their uniqueness and personality. To model such microsurfaces, high definition normal maps are very effective. The works of Yan et al. [21,22] enable the rendering of such material representations by evaluating a microfacet based BRDF related to a whole ray footprint. Still, in specific configurations and especially at grazing angles, their method does not fully capture the expected material appearance. We propose to build upon their work and tackle the problem of accuracy using a more physically based reflection model. To do so, the normal map is approximated with a mixture of anisotropic, noncentered Beckmann normal distribution functions from which a closed form for the maskingshadowing term can be derived. Based on our formal definition, we provide a fast approximation leading to a performance overhead varying from 5% to 20% compared to the method of Yan et al. [22]. Our results show that we more closely match ground truth renderings than their methods.
Rendering materials such as metallic paints, scratched metals and rough plastics requires glint integrators that can capture all micro‐specular highlights falling into a pixel footprint, faithfully replicating surface appearance. Specular normal maps can be used to represent a wide range of arbitrary micro‐structures. The use of normal maps comes with important drawbacks though: the appearance is dark overall due to back‐facing normals and importance sampling is suboptimal, especially when the micro‐surface is very rough. We propose a new glint integrator relying on a multiple‐scattering patch‐based BRDF addressing these issues. To do so, our method uses a modified version of microfacet‐based normal mapping [SHHD17] designed for glint rendering, leveraging symmetric microfacets. To model multiple‐scattering, we re‐introduce the lost energy caused by a perfectly specular, single‐scattering formulation instead of using expensive random walks. This reflectance model is the basis of our patch‐based BRDF, enabling robust sampling and artifact‐free rendering with a natural appearance. Additional calculation costs amount to about 40% in the worst cases compared to previous methods [YHMR16, CCM18].
We present a method to 3D print surfaces exhibiting a prescribed varying field of anisotropic appearance using only standard fused filament fabrication printers. This enables the fabrication of patterns triggering reflections similar to that of brushed metal with direct control over the directionality of the reflections. Our key insight, on which we ground the method, is that the direction of the deposition paths leads to a certain degree of surface roughness, which yields a visual anisotropic appearance. Therefore, generating dense cyclic infills aligned with a line field allows us to grade the anisotropic appearance of the printed surface. To achieve this, we introduce a highly parallelizable algorithm for optimizing oriented, cyclic paths. Our algorithm outperforms existing approaches regarding efficiency, robustness, and result quality. We demonstrate the effectiveness of our technique in conveying an anisotropic appearance on several challenging test cases, ranging from patterns to photographs reinterpreted as anisotropic appearances.
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