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Thriftweed

Transfer Attribute - Parameters

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Hi there,

I have an hopefully straightforward issue that I can't seem to figure out. 

I'm just starting to explore accessing the parameters of different nodes but I'm having a hard time understanding why sometimes it works and sometimes it doesn't. 

 

I'm using attribute transfer to create a falloff and using it to drive certain parameters, 

It works on parameters like @height of a mountain sop but it doesn't seem to work with transform nodes or deformers.  

 

I'm sure I'm missing something fundamental as to how this all works. 

 

I've attached a hip file with a few examples 

Any pointers would be greatly appreciated! 

Cheers 

 

 

AttributeTransfer-Parm.hiplc

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You are confusing attributes with parameters. Attributes are data attached to geometry primitives (like points or polygons). Parameters are knobs, widgets visible in GUI which control node's behavior. Now, while some nodes are aware of certain attributes and can modify their behavior based on per point/prim values (usually acting like a multiplier on parameters), it's not obligatory. It's an extra feature provided whenever (a) it makes sense (b) it's possible (c) someone at SideFX was fancy about it.

It's specially easy to make an attributes aware node if it's implemented in VEX (and many Houdini's nodes are wrappers on VEX snippets), but it's not the requirement (some C++ nodes use attributes as well) . Anyhow, you should always refer to the docs to find out what attributes (if any) are supported by the particular node. In your example scene MountainSOP was working with height, because VEX overrides by default input parameters values with geometry attributes of the same name.

I modified your scene to somewhat working version to illustrate the concept. Note though that not always varying parameter's value per point/prim makes sense or is obvious to implement. For example my soft transform with point cloud filtering doesn't work, but I didn't have time to think about it.

 In all cases these are linear interpolations which might or might not work for particular scenerio (which is exactly the reason why attributes cannot, in general, control all parameters). 

 

 

AttributeTransfer-Parm.hipnc

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Thank you so much for looking into this it's very helpful!

Ah I see where I've been going wrong, it's so much clearer now thank's for the explanation. 

It's still a bit too advanced for me at this stage but it is very slowly starting to make sense.

 

Thanks again 

 

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