Approximate ambient occlusion for trees

Abstract

Natural scenes contain large amounts of geometry, such as hundreds of thousands or even millions of tree leaves and grass blades. Subtle lighting effects present in such environments usually include a significant amount of occlusion effects and lighting variation. These effects are important for realistic renderings of such natural environments; however, plausible lighting and full global illumination computation come at prohibitive costs especially for interactive viewing. As a solution to this problem, we present a simple approximation to integrated visibility over a hemisphere (ambient occlusion) that allows interactive rendering of complex and dynamic scenes. Based on a set of simple assumptions, we show that our method allows the rendering of plausible variation in lighting at modest additional computation and little or no precomputation, for complex and dynamic scenes.

Analytic ambient occlusion using exact from-polygon visibility

“…Context based solutions. There are other studies which target specific applications, such as molecular visualization [15], tree [16] or character [17,18] rendering. These methods are based on approximations or assumptions valid only in a particular context and are therefore not related to this work.…”

Hardware accelerated ambient occlusion techniques on GPUs

“…There are other research papers such as [Kontkanen and Aila 2006;Hegeman et al 2006;Wassenius 2005] targeting specific applications such as animated characters, trees, etc. Solely precomputation based static methods such as PRT (Precomputed Radiance Transfer) [Sloan 2006;Sloan et al 2002;James and Fatahalian 2003], baked-AO (such as [ShadeVis 2006]) are less flexible yet simpler solutions for static ambient occlusion.…”

“…One major advantage of the distant-occluder approach as compared to [Ren et al 2006;Bunnell 2005;Hegeman et al 2006;Kontkanen and Laine 2005] is that we use the various GPU units to their advantage. We achieve frame-rates in excess of 80 fps on a nVidia GeForce 8800GTX for over 6,000 spheres (using the distantoccluder approach alone); this is because, regardless of the number of spheres present in the scene, the rasterizer clips the billboards to the view-frustum and generates the targeted fragments.…”

Real-Time Illumination of Foliage Using Depth Maps

“…Other authors [11] adaptat [10] to the GPU so that the ambient occlusion is computed directly in the fragment shader. Another approach for real-time illumination of trees is [12]. In this work, ellipsoidal occluders that describe the shape of the tree are evaluated at run time.…”