We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps ---low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.
Figure 1: Real-time rendering (58fps on a NVIDIA GTX285 at 1280 × 720 resolution) of the "Crytek Sponza" scene (262k triangles, available at http://www.crytek.com/downloads/technology/) using our method for indirect illumination with 3 cascades of light propagation volumes (LPVs, with 50, 25 and 12.5 meters grid spacing; the scene extend is about 37 × 15 × 22m 3 ). Lights, camera, and geometry can be fully dynamic. The time required for the computation of the indirect illumination is about 10 milliseconds only. Right: We add participating media (single-scattering) effects rendering at 34 fps by ray marching through the LPV. The overhead for ray marching is about 18ms. AbstractThis paper introduces a new scalable technique for approximating indirect illumination in fully dynamic scenes for real-time applications, such as video games. We use lattices and spherical harmonics to represent the spatial and angular distribution of light in the scene. Our technique does not require any precomputation and handles large scenes with nested lattices. It is primarily targeted at rendering single-bounce indirect illumination with occlusion, but can be extended to handle multiple bounces and participating media. We demonstrate that our method produces plausible results even when running on current game console hardware with a budget of only a few milliseconds for performing all computation steps for indirect lighting. We evaluate our technique and show it in combination with a variety of popular real-time rendering techniques.
Modeling multiple scattering in microfacet theory is considered an important open problem because a non-negligible portion of the energy leaving rough surfaces is due to paths that bounce multiple times. In this paper we derive the missing multiple-scattering components of the popular family of BSDFs based on the Smith microsurface model. Our derivations are based solely on the original assumptions of the Smith model. We validate our BSDFs using raytracing simulations of explicit random Beckmann surfaces. Our main insight is that the microfacet theory for surfaces with the Smith model can be derived as a special case of the microflake theory for volumes, with additional constraints to enforce the presence of a sharp interface, i.e. to transform the volume into a surface. We derive new free-path distributions and phase functions such that plane-parallel scattering from a microvolume with these distributions exactly produces the BSDF based on the Smith microsurface model, but with the addition of higher-order scattering. With this new formulation, we derive multiple-scattering micro-facet BSDFs made of either diffuse, conductive, or dielectric material. Our resulting BSDFs are reciprocal, energy conserving, and support popular anisotropic parametric normal distribution functions such as Beckmann and GGX. While we do not provide closed-form expressions for the BSDFs, they are mathematically well-defined and can be evaluated at arbitrary precision. We show how to practically use them with Monte Carlo physically based rendering algorithms by providing analytic importance sampling and unbiased stochastic evaluation. Our implementation is analytic and does not use per-BSDF precomputed data, which makes our BSDFs usable with textured albedos, roughness, and anisotropy.
Figure 1: Our method computes global illumination by rasterizing many thousands of tiny micro-buffers (middle left) in parallel, using a sub-linear point rendering technique with an importance-warped projection. Two interior levels of the hierarchy with 1M points are shown on the left. The middle image renders at 1.1 Hz (512 × 512 res.). The right scene (700K triangles converted to 1M points) renders at 0.7 Hz. AbstractRecent approaches to global illumination for dynamic scenes achieve interactive frame rates by using coarse approximations to geometry, lighting, or both, which limits scene complexity and rendering quality. High-quality global illumination renderings of complex scenes are still limited to methods based on ray tracing. While conceptually simple, these techniques are computationally expensive. We present an efficient and scalable method to compute global illumination solutions at interactive rates for complex and dynamic scenes. Our method is based on parallel final gathering running entirely on the GPU. At each final gathering location we perform micro-rendering: we traverse and rasterize a hierarchical point-based scene representation into an importance-warped microbuffer, which allows for BRDF importance sampling. The final reflected radiance is computed at each gathering location using the micro-buffers and is then stored in image-space. We can trade quality for speed by reducing the sampling rate of the gathering locations in conjunction with bilateral upsampling. We demonstrate the applicability of our method to interactive global illumination, the simulation of multiple indirect bounces, and to final gathering from photon maps.
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