haggi Posted December 18, 2010 Share Posted December 18, 2010 If I have a transparent object with refraction like the one attached, then I get a complete opaque alpha channel. From mentalray I normally get a alpha in the refractions. Is there a way to get this kind of alpha in mantra too? I know this may be a stupid question... Quote Link to comment Share on other sites More sharing options...
Macha Posted December 19, 2010 Share Posted December 19, 2010 (edited) If you use the mantra surface material then try the opacity options (especially the alpha-falloff). Houdini makes a distinction between alpha and opacity. Refraction is considered opaque. As far as I know you either have to use the opacity options, or make your own imageplane that you can then use and manipulate in compositing. You have to export an extra image plane as Of, or use your own custom setup. Edited December 19, 2010 by Macha Quote Link to comment Share on other sites More sharing options...
brianburke Posted December 19, 2010 Share Posted December 19, 2010 (edited) If I have a transparent object with refraction like the one attached, then I get a complete opaque alpha channel. From mentalray I normally get a alpha in the refractions. Is there a way to get this kind of alpha in mantra too? I know this may be a stupid question... this is super chill to do in mantra. if you do your refractions with the gather vop or the ray trace vop (I'd recommend the ray trace vop because its faster and easier to use) you can return the alpha from the hit object and output it as alpha from your shader. If you use the fresnel vop to come up with the input dir for the ray trace vop and mult the output by the same, you'll have resonably physically correct reflections even though this is not using the sweet new multiple importance sampling h11 stuff. I suppose it doesn't really matter though, since you're pretty much throwing physical accuracy out of the window by doing this anyway, but I'm sure you have your reasons... good luck dude Edited December 19, 2010 by brianburke Quote Link to comment Share on other sites More sharing options...
Macha Posted December 19, 2010 Share Posted December 19, 2010 Excellent trick! Quote Link to comment Share on other sites More sharing options...
Macha Posted December 19, 2010 Share Posted December 19, 2010 (edited) Haggi, if I understand Bunker correctly, this is the network: Edit: The refract inputs should probably be normalized prior to connecting. Edited December 19, 2010 by Macha Quote Link to comment Share on other sites More sharing options...
haggi Posted December 20, 2010 Author Share Posted December 20, 2010 Haggi, if I understand Bunker correctly, this is the network: Edit: The refract inputs should probably be normalized prior to connecting. Thanks a lot! I'll try it. Quote Link to comment Share on other sites More sharing options...
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