Figure 1: Comparisons of standard Shadow Mapping with Sub-Pixel Shadow Mapping (SPSM). On the left, the YeahRight model (≈ 150 000 polys) using a 1K × 1K shadow map rendered in 11 ms with SPSM. On the right, a large City model (≈ 2 300 000 polys) rendered using a single 2K × 2K shadow map in 41.6 ms. SPSM brings sub-pixel accuracy to shadow maps, avoiding aliasing artifacts while preserving the rendering speed. AbstractThe limited resolution of shadow maps (SM) may result in erroneous shadowing, yielding artificially jagged edges and temporally crawling shadows even using perspective optimization techniques. We introduce Sub-Pixel Shadow Maps (SPSM) for realtime shadow-mapping with sub-pixel precision. Our technique is based on the storage of a fixed-size partial representation of the scene geometry using conservative rasterization, combined with an original reconstruction of shadow edges. With only a small computational overhead our method avoids both perspective and projection aliasing. SPSM reconstructs shadow boundaries with thin details and high temporal consistency even using low resolution shadow maps. Our solution can also be used in conjunction with perspective optimization techniques where temporal and projection aliasing is hardly addressed. SPSM can particularly be used in demanding application such as games and real time rendering engines.
Figure 1: Our technique provides sub-pixel accuracy to shadow maps, avoiding aliasing artifacts while preserving the rendering speed (left). We reconstruct shadow edges by combining an estimate of the shadow tangent (right) with partial geometry information.The limited resolution of shadow maps may result in erroneous shadowing, yielding artificially jagged edges ( Figure 1) and temporally crawling shadows even using perspective optimization techniques. Dai et al. [2008] propose an explicit storage of geometry within shadow map texels to avoid aliasing. Each texel stores the coordinates of the closest triangle only, potentially leading to false negatives in the intersection computation while incurring large memory consumption. These artifacts are reduced by intersecting the triangles stored in numerous neighboring texels, resulting in significant performance hit while still missing some intersections. We introduce Sub-Pixel Shadow Maps (SPSM) for real-time shadow mapping with sub-pixel precision. Our technique is based on the storage of a fixed-size partial representation of the scene geometry using conservative rasterization, combined with an original reconstruction of shadow edges. The Sub-Pixel Shadow MapStoring triangle information within the shadow map introduces two main challenges. First, most hardware rasterizers generate fragments only if the center of the fragment is covered by the considered triangle. A geometry-based shadow map [2008] may thus lack information in the texels corresponding to shadow edges, where precision is crucial. The second challenge is the presence of several triangles rasterized at a same texel position. Ideally, each texel should store an arbitrarily large list of overlapping triangles.We first enforce the generation of fragments for the entire coverage of the triangles using Conservative Rasterization [Hasselgren et al. 2005]. We then generate the SPSM by rendering the scene from the light viewpoint, storing vertex information for the closest triangle only. We pack the coordinates in SPSM space within 128-bit using a novel compression scheme for compact storage of depth derivatives (Figure 2). At the rendering stage we project each visible point p in light space and determine whether p lies on the triangle stored in the corresponding SPSM texel. If so, conservative rasterization guarantees that p is not occluded. Fully lit zones are then rendered using a single SPSM lookup. Otherwise, we intersect the light ray from p with the triangle. While finding an occlusion ensures shadowing, the lack of intersection may be due to missing geometry. We then intersect the light ray with the triangles stored in the 3 × 3 neighborhood of the texel. If needed, we compensate for occlusion incertainty by analytically reconstructing the shadow edge.Even though our representation is partial, an accurate shadow edge can be obtained by linking edge vertices. Considering the result of depth comparisons for the point p in the 3 × 3 neighborhood, we first deduce an approximate light-space tangent to th...
We introduce analytic approximations for accurate real-time rendering of surfaces lit by non-occluded area light sources. Our solution leverages the Irradiance Tensors developed by Arvo for the shading of Phong surfaces lit by a polygonal light source. Using a reformulation of the 1D boundary edge integral, we develop a general framework for approximating and evaluating the integral in constant time using simple peak shape functions. To overcome the Phong restriction, we propose a low cost edge splitting strategy that accounts for the spherical warp introduced by the half vector parametrization. Thanks to this novel extension, we accurately approximate common microfacet BRDFs, providing a practical method producing specular stretches that closely match the ground truth in real-time. Finally, using the same approximation framework, we introduce support for spherical and disc area light sources, based on an original polygon spinning method supporting non-uniform scaling operations and horizon clipping. Implemented on a GPU, our method achieves real-time performances without any assumption on area light shape nor surface roughness.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.