![]() The idea for the ray-height-field intersection is to replace the linear search with an aggressive spaceleaping approach, which is immediately followed by a binary search. We call the new space-leaping algorithm relaxed cone stepping (RCS), as it relaxes the restriction used to define the radii of the cones in CSM. In this chapter, we describe a new ray-height-field intersection strategy for per-fragment displacement mapping that combines the strengths of both cone step mapping and binary search. ![]() Its results are shown in Figure 18-1c, which also highlights the technique's artifacts.įigure 18-1 Comparison of Four Different Ray-Height-Field Intersection Techniques Used to Render a Relief-Mapped Surface from a 256x256 Relief Texture We call this approach quad-directional cone step mapping (QDCSM). Using an extension to CSM that consists of employing four different radii for each fragment (in the directions north, south, east, and west), one can just slightly reduce the occurrence of these artifacts. However, because CSM uses a conservative approach, the rays tend to stop before the actual surface, which introduces different kinds of artifacts, highlighted in Figure 18-1b. Cone step mapping (CSM) (Dummer 2006) provides a clever solution to accelerate the intersection calculation for the average case and avoids skipping height-field structures by using some precomputed data (a cone map). Several space-leaping techniques have since been proposed to accelerate the ray-height-field intersection and to minimize the occurrence of aliasing (Donnelly 2005, Dummer 2006, Baboud and Décoret 2006). While the binary search converges very fast, the linear search (required to avoid missing large structures) is prone to aliasing, by possibly missing some thin structures, as is evident in Figure 18-1a. In all its variations, the ray-height-field intersection is performed using a binary search, which refines the result produced by some linear search procedure. The technique has been further extended to render correct silhouettes (Oliveira and Policarpo 2005) and to handle non-height-field surface details (Policarpo and Oliveira 2006). To address these issues, an image-based technique called relief mapping has recently been introduced for adding per-fragment details onto arbitrary polygonal models (Policarpo et al. ![]() Although synthesizing realistic pictures requires simulating this interaction as faithfully as possible, explicitly modeling all the small details tends to be impractical. The presence of geometric details on object surfaces dramatically changes the way light interacts with these surfaces. Instituto de Informática-UFRGS 18.1 Introduction You can also subscribe to our Developer News Feed to get notifications of new material on the site.Ĭhapter 18. The CD content, including demos and content, is available on the web and for download. GPU Gems 3 GPU Gems 3 is now available for free online! ![]()
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