Oh, bummer. Thanks so much for the background info.
I suppose there isn't a way for a Material to modify the VertexContext in vertex_shader, but still pass the original VertexContext to the shading tree, right? The thing is, I've been using some of the predefined attributes to pass arbitrary data to the fragment_shader. My only concern is that if you stack another material that wants to use that attribute, it will pick up my modified VertexContext, right? Not a big deal, since this material is rather specific, but just wanted to see if there was a different way to tackle this. Thanks, Ivan On Wed, Sep 14, 2011 at 3:23 PM, Jonathan Egstad <jegs...@earthlink.net>wrote: > > Is it possible to add attributes other than the predefined ones to a > VArray passed through the vertex shader, and have the vertex_shader > interpolate them? > > Short answer - not really... > > Long answer - the VArray structure was originally just a wrapper around a > Pixel structure which contained 1024 floats. The Channel3D assignments were > defaults with the ability to declare add'l varying attributes - but it was > quickly identified as a memory hog during rasterization and was trimmed down > drastically. Unfortunately much of the varying attribute support went away > with that change - and the AttribContext copy_to_channels() is a remnant. > > The ultimate answer is to not pre-cache all the interpolating vertex data > as is done now but to generate it on demand - I think with today's CPUs and > the large number of engine threads that swapping CPU time for memory in this > part of the algorithm (you'd end up recalculating the same vertex data > possibly hundreds of times) would be a big win - especially since rendering > large poly scenes can often take a machine into swap. > > -jonathan > > > > So far, if I want to pass some arbitrary info onto the fragment_shader, > I've just been forcing it into any of the predefined slots (PW, PL, N...) > that I don't need in the fragment shader. > > But I was wondering if it's possible to add new attributes. > > > > I notice AttribContext has a "copy_to_channels" method that sounds like I > could use for this, but I'm not sure how to go about creating a new > AttribContext, and filling it with my data. > > > > In any case, would that be the best approach to append arbitrary data to > a Varray? Can anyone share any pointers/examples/help? > > > > Many thanks, > > Ivan > > _______________________________________________ > > Nuke-dev mailing list > > Nuke-dev@support.thefoundry.co.uk, http://forums.thefoundry.co.uk/ > > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-dev > > _______________________________________________ > Nuke-dev mailing list > Nuke-dev@support.thefoundry.co.uk, http://forums.thefoundry.co.uk/ > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-dev >
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