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Realistic Rendering of thin transparent layers bounded by rough surfaces involves substantial expense of computation time to account for multiple internal reflections. Resorting to Monte Carlo rendering for such material is usually impractical since recursive importance sampling is inevitable. To reduce the burden of sampling for simulating subsurface scattering and hence improve rendering performance, we adapt the microfacet model to the material with a single thin layer by introducing the extended normal distribution function (ENDF), a new representation of this model, to express visually perceived roughness due to multiple bounces of reflections and refractions. With such a representation, both surface reflection and subsurface scattering can be treated in the same microfacet framework, and the sampling process can be reduced to only once for each bounce of scattering. We derive analytical expressions of the ENDF for several cases using joint spherical warping. We also show how to choose proper shadowing-masking and Fresnel terms to make the proposed bidirectional scattering distribution function (BSDF) model energy-conserving. Experiments demonstrate that our model can be easily incorporated into a Monte Carlo path tracer with little extra computational and storage overhead, enabling some real-time applications.

In this paper, we present an efficient framework for editing the appearance of measured materials. First, we separate the material data into diffuse and specular parts, which is important for measured BRDFs since editing without distinguishing the two parts makes the results less predictive. Additionally, the albedo of each part is calculated for later color editing. Next, we use a novel method to cluster the materials by their gloss levels and select the representative material of every level. With this at hand, the roughness, i.e., shape of the specular highlights can be adjusted among different levels. Finally, we reconstruct the edited materials which can be directly used in both online and offline rendering. We test the framework on the MERL dataset to validate the effectiveness of our method.

We introduce an analytical BRDF model tailored to the realistic rendering of retroreflective materials. Though these specially-designed materials are frequently encountered in our daily life, such as high-visibility clothing and traffic signs, their reflectance behaviors are barely analyzed and simulated in a physically meaningful manner in computer graphics. To understand how retroreflection is actually generate, we conduct a detailed optical analysis on a typical prismatic sheet which is the most widely used retroreflector in the material industry. In particular, the effective retroreflective area of the sheet is studied theoretically and experimentally. Based on the study, we derive a practical BRDF model that takes into account all types of reflection from the sheet, including mirror reflection, retroreflection, and diffuse reflection. Experiments confirm that our BRDF can produce visually pleasing rendered images with high fidelity retroreflection effects which closely match those generated by the prismatic sheet.

Detailed modeling of appearance affected by dust coverage is challenging because of the numerous physical and material factors on which it depends. The two principal roadblocks are the complexity of simulating dust particle deposition and the difficulty of accurately depicting the reflectance. In this paper, we present a practical framework for simulating and rendering the appearance of objects covered by the layered dust of spatially varying thickness. First, a fast evaluation approach is proposed to compute the dust's thickness distribution based on a surface's inclination and stickiness properties, as well as surface exposure and local stability. Then, to ensure high fidelity of light scattering and real-time performance, we render the scene based on a revised Kubelka---Munk model implemented on the GPU, including the effects of external and internal surface reflection. Finally, experimental results reveal that our framework can produce visually convincing dusty objects of arbitrary complexity in real time.

Line segment sampling has recently been adopted in many rendering algorithms for better handling of a wide range of effects such as motion blur, defocus blur and scattering media. A question naturally raised is how to generate line segment samples with good properties that can effectively reduce variance and aliasing artifacts observed in the rendering results. This paper studies this problem and presents a frequency analysis of line segment sampling. The analysis shows that the frequency content of a line segment sample is equivalent to the weighted frequency content of a point sample. The weight introduces anisotropy that smoothly changes among point samples, line segment samples and line samples according to the lengths of the samples. Line segment sampling thus makes it possible to achieve a balance between noise (point sampling) and aliasing (line sampling) under the same sampling rate. Based on the analysis, we propose a line segment sampling scheme to preserve blue-noise properties of samples which can significantly reduce noise and aliasing artifacts in reconstruction results. We demonstrate that our sampling scheme improves the quality of depth-of-field rendering, motion blur rendering, and temporal light field reconstruction.

This paper proposes a real-time system to render with layered materials by using a linearly filterable reflectance model. This model effectively captures both surface and subsurface reflections, and supports smooth transitions over different resolutions. In a preprocessing stage, we build mip-map structures for both surface and subsurface meso-structures via fitting their bumpiness with mixtures of von Mises Fisher (movMF) distributions. Particularly, a movMF convolution algorithm and a movMF reduction algorithm are provided to well-approximate the visually perceived bumpiness of the subsurface with controllable rendering complexity. Then, both surface and subsurface reflections are implemented on GPUs with real-time performance. Experimental results reveal that our approach enables aliasing-free illumination under environmental lighting at different scales.

We present a novel approach for real-time rendering of transparent objects with multi-scale rough refraction under all-frequency environmental lighting. In our rendering system, the normal distribution function (NDF) of the surface bumps is expressed via mixtures of von Mises-Fisher (vMF) distributions, while the corresponding perturbation of refracted rays (RDF) can be approximated as a spherical warp of NDF, taking into account correction factors. Under the assumption of two-sided refraction, we first generate the vMF lobes of the front surface refraction. Based on these lobes, we then estimate the RDF of back surface as a warped convolution of macroscopic and microscopic NDFs within the footprint of each lobe. Moreover, summed-area tables and dual-paraboloid maps are adopted to efficiently represent the environmental lighting in order to support fully dynamic lighting conditions. We finally get a coherent rendering at the different scales that reproduces high-quality meso- and micro-geometric effects under real-time performance.

The illumination of rough refraction is challenging due to the complex integrations of scattered lights from multiple directions. Prefiltered environment map is able to eliminate the comprehensive integrations, but the precomputation stage protects it from being adapted into dynamically varying environmental lighting. We propose a real-time method for rendering rough refraction, supporting dynamically changing lighting, geometries and materials. Environment maps are efficiently compressed by summed area table (SAT), whose construction only costs several milliseconds. Meanwhile, rough refraction effects are approximated by our lobe merging method. Solid results of our approach are demonstrated by comparing with ground truth results generated with a path tracing engine.

Complex natural lighting provides better realism compared to traditional artificial lights, which has been increasing in real-time graphic applications, such as video games and virtual reality. However, rendering with complex natural illumination proves quite costly owing to a spherical space integral. This paper addresses the problem of real-time rendering scenes under complex environment lighting that captures soft shadows and glossy reflections. The environment lighting is separated into low-frequency lighting component and highlight component based on a rejection-based sampling method. Scenes lit under low-frequency lighting are approximated via spherical harmonic lighting, while highlight illumination effects such as soft shadows and glossy reflections are simulated by a small set of sampled virtual point lights (VPL). Experimental results demonstrate that our method can be run in real-time under complex natural lighting without precomputation.

Dynamic environment lighting has been increasing in real-time graphics applications, such as 3D games and virtual environment applications because of its better realism compared to the traditional lights. However, rendering under dynamic environment lighting is sophisticated due to a complex hemispherical space integral operation. Spherical harmonics are used to illuminate diffuse surface in real-time. Screen space ambient occlusion is adopted to approximate soft shadows due to occlusion. Results show that the whole process can run in real-time with little precomputation.

E-Sport is a newly emerging research field, especially in China, which has attracted many people’s attention. In this paper, an innovative distributed online game platform is designed for fitness-oriented E-Sports, supporting multi-players or athletes. To provide users with more sense of immersion, technologies of virtual reality and sport simulation have been integrated into such system. Taking prototype system of Virtual Network Marathon as an example, detail designs are focused on the five aspects: story design, network communication, human computer interface, hardware interface and 3D render engine. All these design philosophies gain advantages of scale expandable, functions extendable, an efficient communication protocol and real-time rendering. Users at a distance can deeply immerse into virtual environment and enjoy exercise, competition and entertainment. Implementation of system is also described to validate the feasibility of our method.