Temporally Coherent Adaptive Sampling for Imperfect Shadow Maps

Abstract

We propose a new adaptive algorithm for determining virtual point lights (VPL) in the scope of real-time instant radiosity methods, which use a limited number of VPLs. The proposed method is based on Metropolis-Hastings sampling and exhibits better temporal coherence of VPLs, which is particularly important for real-time applications dealing with dynamic scenes. We evaluate the properties of the proposed method in the context of the algorithm based on imperfect shadow maps and compare it with the commonly used inverse transform method.The results indicate that the proposed technique can significantly reduce the temporal flickering artifacts even for scenes with complex materials and textures. Further, we propose a novel splatting scheme for imperfect shadow maps using hardware tessellation. This scheme significantly improves the rendering performance particularly for complex and deformable scenes. We thoroughly analyze the performance of the proposed techniques on test scenes with detailed materials, moving camera, and deforming geometry.

Modified filtered importance sampling for virtual spherical Gaussian lights

“…The frame buffer and reflective shadow map (RSM) resolutions are 1920×1088 and 512 2 , respectively. A tessellation-based imperfect shadow map [15] of resolution 64 2 is employed to evaluate the visibility of each VSGL. To estimate a viewdependent PDF on the reflective shadow map using the bidirectional reflective shadow mapping method, 2048 VSGLs without shadow maps are generated on the G-buffer.…”

“…Using this modification for VSGL generation, we are able to render glossy indirect illumination with fewer artifacts than the 8 Caustics rendered using our method with the same PDF (514-triangle scene). Kernel centers of the upper row and lower row are generated using hierarchical sample warping [12] and the MetropolisHastings-based temporally coherent sampling [15], respectively. Due to a lack of stratification, Metropolis-Hastings produces noticeable artifacts.…”

“…Therefore, it can increase flickering artifacts, even though the total variance can be reduced. To take such dynamic PDFs into account, Barák et al [15] introduced a temporally coherent sampling technique based on the MetropolisHastings algorithm for static light sources. They also proposed tessellation-based imperfect shadow maps to reduce memory usage.…”

“…Although the Metropolis-Hastings algorithm can be used for temporally coherent sampling [15], it is limited to static light sources and has a lack of stratification. This problem induces noticeable artifacts especially for caustics (Fig.…”

Sequential Monte Carlo instant radiosity

“…We also shortly cover temporal ltering, a method unrelated to Instant Radiosity that also Moving fewer VPLs. Both Prutkin et al [2012] and Barák et al [2013] extend the real-time importance sampling method by Ritschel et al [2011] to minimize the movement of VPLs between frames.…”