jimmyb Posted June 26, 2003 Share Posted June 26, 2003 Does anyone know how make a subsurface type shader in VOPS? I was thinking of some way take a fresnal and Luminance VOP, and plugging them into the Point Position of the shader. There's a few neat Rman tutorials that use depth map/Zdepth to fake it.......... http://zj.deathfall.com/trans.htm Anyone got any ideas? Quote Link to comment Share on other sites More sharing options...
David Gary Posted June 26, 2003 Share Posted June 26, 2003 A general idea i had about faking subsurface scattering/ transluency ( without any raytracing, and with "any" shader ) is to composite , ( in fact, many compositing here) the visible face of an object and the invisible face rendered separately, with an enhanced z-depth information... How to isolate the visible part and the invisible part, and how to make the invisible part visible: by making the visible part invisible! ha! ha! i explain: Take the example of the sphere: some faces are "facing the camera" : front faces, where N.i<0 , the other are not. Most of the time (when the surface is closed), the back faces ( where N.i>0 ) are hidden by the front faces) To make them visible (and only them) (the back faces) turn opacity to 0 for (N.i<0)-faces ( that's what i meant by "making the visible part invisible") turn opacity to 1 for (N.i>0)-faces ( that's what i meant by "making the invisible part visible"). the pass for the front faces is obvious. Then, for each, encode the distance to the camera (i don't know how z-depth works with opacity, i should try), that means (ahem) four passes and... composite using the distance between the two depth images to control transparency. (i don't know mantra very much, but that may be done in a single render pass ) I hope i was clear enough... and hope it helps! tell me if it works and make it better! and/or easier... t'was just an idea.. ( i did not even try to achieve this effect (i've got bugs with my Apprentice version )). I had got this idea from the exact paper you mentioned (very good tips at deathfall!). i don't know if fresnel alone works. You have to encode an information about a volume, that is about, at least, two planes. so. just write shaders... vex vex vex vex vex vex vex vex vex vex!! cheers Quote Link to comment Share on other sites More sharing options...
David Gary Posted June 26, 2003 Share Posted June 26, 2003 ahem i forgot to say that, like deathfall tip from Christophe Hery, it cannot work in any case! only for simple models... it's just cheating ( Tchi' Ting' ). Quote Link to comment Share on other sites More sharing options...
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