I think the particle-system operates with chunks of memory and adding 
user-defined attributes isn't possible (yet?).If the type isn't per-particle as 
well: could you derive from Particles (Primitive) and add an extra field there?
> Date: Thu, 6 Dec 2012 08:48:25 +0800> From: [email protected]
> To: [email protected]
> Subject: [Nuke-dev] Adding attributes to particles
> 
> So I have this node that adds attributes to geo, specifically "size" and 
> "type", so that this geo can be rendered as some sort of particles, 
> downstream.
> 
> This node used to be derived from GeoOp, so geometry_engine() was called 
> by Nuke and added/modified these attributes.
> 
> But GeoOp being the base had the side effect that particle nodes 
> wouldn't accept it as an input. So now the node is derived from 
> ParticleBehavior. The problem is now that geometry_engine() is not 
> called anymore, when the downstream node is a ParticleOp of some sort.
> 
> Interestingly, geometry_engine() is still called when the node is 
> directly connected to a Scene (this is probably a bug in Nuke but it is 
> great because we want this to happen!)
> 
> What I want is a callback, like geometry_engine(), that allows me to 
> modify/add attributes on the incoming particles.
> There is applyBehavior() and I use that successfully for "size" if the 
> input is particles. But if the input is geo, this doesn't work as the 
> geo doesn't have any size attribute. Also there seems to be no way to 
> add custom attributes in applyBehavior().
> 
> Any suggestions? I tried deriving the node from both bases but this gave 
> me lots of ambiguity errors that I could never completely get rid of.
> I also think it wouldn't solve it because if the downstream node was a 
> ParticleOp, geometry_engine() wouldn't get called in any case, innit?
> 
> In short: how do I make a node that allows me to add attributes to 
> particles and which works as an input to Nuke particle nodes?
> 
> .mm
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