It's a long time ago that I did hair with mr, Arnold makes that a breeze now. But I did that always with the rasterizer. If the hair is not to long you could bake the final gathering into a texture and use that to mix it into the shading, which gives you a nice look without too much rendering time. Cheers Chris
Von meinem iPhone gesendet > Am 07.12.2014 um 09:17 schrieb [email protected]: > > Thanks Matt - > interesting - I've come across a custom hair normals shader that was giving a > better, more "tube" or "cone" feel - that gave some more "presence" to the > hairs. (More so at close up) - and in my understanding the flat vs > cylindrical normals was the explanation. But I stand corrected. > Still I've found the crosswise gradient as a bump useful on hair (and grass) > to give them a less flat feel. > > You're very right of course that flat ribbon is much more geometry efficient > than cylinder - with all the memory advantages - but when 3Delight renders > those beautiful hair 'tubes' without any geometric artifacts, much more > convincing looking and much faster and at a fraction of the memory overhead - > it's hard to complement MR on its very efficient choice of the flat ribbon. > (apples and oranges, I know) > > Yes, I did my own digging in rendersettings for hair on Barnyard. Having a > screenful of unique characters, each with several patches of hair, with > wildly different styles and requirements, 8 years ago, on MR, with > requirement for a plethora of lights in the scene, all of them with > (soft)shadows. The default settings fall down quick, as in: results not good > enough plus too slow, but there is a lot to be got out MR in that respect > yet. (which was the main reason for my reply to OP) I recall rasterizer and > shadowmaps as two main ones for making it look better (also filtering and > sampling ofcourse) - and then all those little parameters to get the > rendertimes down. BSP, raydepth, and careful use of partitions and visibility > settings! > And from that production (and others after) I've never had the feeling of > hair being a real bottleneck for lighting. Particles and effects much more so > in those pre-pre-ICE days. > > Cheers > > -----Original Message----- From: Matt Lind > Sent: Sunday, December 07, 2014 2:03 AM > To: [email protected] > Subject: realistic hair shading SI-MR > > @Peter > > MR hair geometry is flat ribbon, but the normal is computed from a virtual > cylinder like a normal map with full control over shaft radius and taper > along the length. For most practical purposes it should create the desired > look. Using the utility shaders (math/lookup nodes) available in the > rendertree, you can read hair UV coords and surface normal yourself if you > want to shade them differently than the provided hair shaders. Mental ray > stores hair information in the state which can be accessed by any shader > which cares to dig into that information. > > The reason for flat ribbon is to allow hair to be represented as physical > geometry which can be styled and groomed, respond to dynamics, and use > material/texture shaders for shading while keeping memory consumption > low/reasonable (representing hair as geometry is hugely expensive). Mental > ray does offer true cylinder hair, but to get cylinder hair would require > the hair shader to be implemented as a volume shader (which would have it's > own set of issues). I believe that was how the original softimage hair > shader from 10 years ago was implemented. It rendered hair convincingly for > the basics such as highlights, but most people didn't like it because as a > volume shader it did not permit styling and grooming (or at least not much > control over it), and rendered quite slow with frequent crashing as mental > ray volumes can be a bit finicky. > > I experimented with hair rendering in mental ray for Barnyard all those > years ago. From a purely technical point of view, writing shaders for hair > isn't too hard - it's just standard material/texture shader with additional > metadata for the hair. The key to getting results is being smart with your > render settings. You must be stringent on ray depth, recursion, shadow > type, memory limits, and so on. Setting them too generously will make your > render times go through the roof as you're telling mental ray to wander and > find things to do which probably aren't necessary. the default render > settings in Softimage are probably too generous for hair. > > > Matt >
