ykcosmo Posted December 4, 2004 Share Posted December 4, 2004 what is "fresnel reflections"? can anyone show me a pic? Quote Link to comment Share on other sites More sharing options...
sibarrick Posted December 4, 2004 Share Posted December 4, 2004 Sorry don't have any pictures but just grab yourself a glass or a glass bottle and have a look at it. Fresnel reflections are the reflections that happen as the glass turns away from you and becomes more reflective and less transparent. Quote Link to comment Share on other sites More sharing options...
michael Posted December 4, 2004 Share Posted December 4, 2004 google is your friend: http://images.google.ca/images?q=fresnel+r...G=Google+Search http://www.cgrenaissance.com/index.php?page=Fresnel Quote Link to comment Share on other sites More sharing options...
stu Posted December 6, 2004 Share Posted December 6, 2004 Happy Holidays! I threw in a dual spec for the car enthusiasts out there. fresnel.zip Quote Link to comment Share on other sites More sharing options...
deecue Posted December 13, 2004 Share Posted December 13, 2004 hey stu, sorry if im missing something basic here, but what exactly is the purpose of the GI light? Is it just to make the render have more pretty lighting for the purpose of showing off the reflections other typical GI reasons.. Or is it actually something needed for the fresnel reflections and affecting it dramatically. i went ahead and just got rid of it and the reflections seemed to stay intact just fine so I'm pretty sure it has nothing to do with them, but just wanted to check and make sure. thanks for the example. dave Quote Link to comment Share on other sites More sharing options...
Jason Posted December 13, 2004 Share Posted December 13, 2004 GI lighting has no effect on fresnel reflections - I'm sure it's just in there for overall prettiness. Quote Link to comment Share on other sites More sharing options...
deecue Posted December 15, 2004 Share Posted December 15, 2004 GI lighting has no effect on fresnel reflections - I'm sure it's just in there for overall prettiness. 15487[/snapback] good to know.. thanks jason. Quote Link to comment Share on other sites More sharing options...
stu Posted December 16, 2004 Share Posted December 16, 2004 Like Jason said, it has no real affect on the fresnel reflection. Because the reflections are being raytraced in this case and there is a bright sphere representing the sky being introduced in the fresnel reflections, I thought I'd cast a general skylight onto the scene with the GI light for the sake of continuity. Quote Link to comment Share on other sites More sharing options...
deecue Posted December 16, 2004 Share Posted December 16, 2004 hey stu, ya know, you should package that fresnel shader and put it in the exchange.. im sure people would appreciate that. just a thought.. Quote Link to comment Share on other sites More sharing options...
Mario Marengo Posted December 16, 2004 Share Posted December 16, 2004 ya know, you should package that fresnel shader and put it in the exchange.. im sure people would appreciate that. 15529[/snapback] That's a good idea, since people tend not to account for fresnel simply because it's not built into the reflection-related VOPs. But I just took a look at the shader, and thought I'd mention (not for your benefit stu, since I'm sure you're aware of it) that weighing reflections by the complement of the EdgeFalloff VOP is not the same as using the fresnel function. Of course, that doesn't mean it's "incorrect", it's just not the same as a fresnel reflection -- although you may well choose to go this way for aesthetic reasons, since it's a gentler, more "spread out" version of the effect. I'm guessing here, but I'd bet that the EdgeFalloff simply returns pow(dot(normalize(N),normalize(I),exp), where exp is the "Edge Falloff" parameter. This basically gives you a cosine curve. Having said that, I agree with deecue, it's a very cool and useful shader just as it is. Thanks for sharing stu! Cheers! Quote Link to comment Share on other sites More sharing options...
stu Posted December 17, 2004 Share Posted December 17, 2004 Hi Mario (your sss work is fantastic! :notworthy: ), Yeah, I've been torn between the fresnel definition and a consistent falloff based on angle of incidence. I've always found that the linear approach seems to be easier to predict in regards to it's behaviour. The purists out there are going to cringe, but I often cheat it even more and give it a baseline "max" and "min" reflection contribution based on the viewing angle so that the user has absolute control and completely ignore the whole "index of refraction" issue. It's not physically accurate, but it's easier for someone to make the picture that they were expecting. I'll add the "min" and "max" methodology when I get a chance. stu Quote Link to comment Share on other sites More sharing options...
Mario Marengo Posted December 17, 2004 Share Posted December 17, 2004 It's not physically accurate, but it's easier for someone to make the picture that they were expecting.I'll add the "min" and "max" methodology when I get a chance. 15538[/snapback] Sounds like a good idea to me. Cheers! Quote Link to comment Share on other sites More sharing options...
stu Posted December 18, 2004 Share Posted December 18, 2004 I was just fooling around with the shader posted above and blatently ripped off an image I posted here about two years ago: I'll post the new version of the shader as soon as I get a chance. stu Quote Link to comment Share on other sites More sharing options...
stu Posted December 29, 2004 Share Posted December 29, 2004 Here's the new version of the shader with the "Min" and "Max" values for the reflections. They are absolute values based on the viewing angle and will allow the user to determine exactly how much reflected colour is being contributed to surfaces at both the facing angles and the grazing angles. fresnel.zip The default "Min" is .1 and the default "Max" is 1. These are multiplied by the actual reflection colour value. The rate of decay is still controlled by the "Reflection Edge Falloff" value. Let me know how it works for you. stu Quote Link to comment Share on other sites More sharing options...
ykcosmo Posted January 3, 2005 Author Share Posted January 3, 2005 thanks for info and happy new year for every one! Quote Link to comment Share on other sites More sharing options...
ykcosmo Posted January 3, 2005 Author Share Posted January 3, 2005 and, I used to know the effect of fresnel reflections, but I don't know it is called "fresnel reflections"...............oh.... Quote Link to comment Share on other sites More sharing options...
MG Posted February 1, 2005 Share Posted February 1, 2005 I was just fooling around with the shader posted above and blatently ripped off an image I posted here about two years ago: I'll post the new version of the shader as soon as I get a chance. stu 15564[/snapback] That's very nice, that's all I can and have to say about it, no criticism or whatsoever. It's without doubt one of the most realistic renders I've ever seen, surely done with Houdini. Quote Link to comment Share on other sites More sharing options...
aracid Posted February 1, 2005 Share Posted February 1, 2005 awesome job stu! but i think thats fake he defnately pulled off all the stickers and stuck it the right way! Quote Link to comment Share on other sites More sharing options...
stu Posted February 3, 2005 Share Posted February 3, 2005 he defnately pulled off all the stickers and stuck it the right way! You mean there's another way? Quote Link to comment Share on other sites More sharing options...
stu Posted April 16, 2005 Share Posted April 16, 2005 Here's a zipped file that contains everything that went into making the cube picture above (geometry, shaders, etc.): cube.zip I've turned some of the settings down so that it renders a bit faster but it's easy enough to turn them back up again. I've also given the ground surface a plain temporary shader, but the original (ground paper) is there as well. I threw the file together pretty quickly so it's probably not the cleanest setup in the world, and the "fake fresnel" shader could use some more options (optional affect spec contribution by "fake fresnel" angle, optional raytraced reflections, etc.). Feel free to make it better and tell me how you did it. Questions, ask 'em. stu Quote Link to comment Share on other sites More sharing options...
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