Article: 28000 of comp.graphics.rendering.renderman From: Olivier3001@hotmail.com Newsgroups: comp.graphics.rendering.renderman Subject: Re: About grids Date: 27 Jun 2006 09:53:11 -0700 Organization: http://groups.google.com Lines: 30 Message-ID: <1151427191.453410.225720@m73g2000cwd.googlegroups.com> References: <1150662724.667204.252970@p79g2000cwp.googlegroups.com> <44971af7$1_2@x-privat.org> <1150802885.054683.171690@c74g2000cwc.googlegroups.com> <44989b73$1_3@x-privat.org> NNTP-Posting-Host: 24.203.170.93 Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Trace: posting.google.com 1151427197 27971 127.0.0.1 (27 Jun 2006 16:53:17 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 27 Jun 2006 16:53:17 +0000 (UTC) User-Agent: G2/0.2 X-HTTP-UserAgent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050920,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: m73g2000cwd.googlegroups.com; posting-host=24.203.170.93; posting-account=FyNS2Q0AAABBrjnjN54E7QAEx96ipyGi Path: x-privat.org!news.glorb.com!postnews.google.com!m73g2000cwd.googlegroups.com!not-for-mail Xref: news.x-privat.org comp.graphics.rendering.renderman:28000 Rick LaMont wrote: > Hector wrote: > > the fact that Reyes algorithm does shading before hiding > > Yes but remember occlusion culling. I would expect it to prevent the > behavior you described where the shader was evaluated on a fully occluded > face of the slab. That's usually possible but not always. One major issue which people often forget is if you do displacement & shading in the same (surface) shader. It's then much harder for the renderer to discard hidden grids because of the potentially large displacement bound. Having separate displacement and surface shaders helps a lot then: the surface can be displaced and discarded without running the surface shader which is typically far more expensive. Another thing is that advanced occlusion culling tests tend to become a speed vs effectiveness tradeoff. You want to drop as many grids as possible but don't want to spend too much time doing so, or waste time on grids which have to be kept in the end. Finally, there's the issue of cracks in the model or dicing of it. While it may look solid on the screen, it takes only a very tiny gap in the surface for a sample to get through and require shading of the "hidden" face. Olivier --- http://www.3delight.com/