[Sidefx-houdini-list] Holding Bone Weights

Louis Dunlevy ld at dneg.com
Sat Jun 16 15:15:02 EDT 2007

Louis Dunlevy wrote:
> ken wrote:
>> technically that is what the second input on the editSOP is supposed 
>> to do. It should be creating a local coordinate system on the deform 
>> and on the rest and then use a quaternion to move the geometry 
>> around. Thing is in practice the more the deformation changes the 
>> less likely the editSOP will be valid. I think of it like a noise 
>> field.. the noisier the field the less  likely you will get a wide 
>> range of use out of the blendshape. strictly speaking that's what we 
>> used for character finaling on the wild.  the problem is no matter 
>> what they do with the coordinate system it still gets a bit wonky in 
>> certain deformations over time. I was intrigued with the radial basis 
>> functionSOP Simon put out, but it can take a while before you get a 
>> strong relationship between the mapping points and the changes you want.
>> for rigging on the other hand this system should be able to give you 
>> a higher percentage of success when you use it for bone angles and 
>> the like. the reality is however, that any deformer after a deformSOP 
>> is slow, so you avoid it. Which means you can use the createeditsop 
>> hscript command to generate a preDeformSOP editSOP result so you can 
>> do use it in a blendSOP above the deform. Again, you can only get so 
>> many in before you start paying the price.. in memory and performance.
>> you idea would be helpful if it was done in the deformSOP. Anything 
>> else isn't as fast or nice once you start getting complicated.
> Yeah, that's exactly what I'm talking about. Layering SOP deformations 
> is cool but slow.
> I've been asking the guys at SESI to consider adding this option to 
> the deform SOP so that it could work in the same way as say the 
> Lattice SOP on a per-bone basis so that only bones that have been 
> explicity moved have an effect. A bone that has moved simply because 
> it's in a hierarchy would not have any effect.
> I love the oriented editing available through the edit SOP via the 
> Morph tool etc. It's a life saver. It is a blendshapes approach 
> however so there are some restrictions there. The other methods you 
> talk about are all valid and very cool and I've used/looked at them 
> all (thanks again Simon for the gooviness). We've put together various 
> other flavours of this on different occasions. It's good to see SESI 
> put in the Attribute Orient SOP too.
> You can access metaball transforms in VEX which is cool.. :-)
> Go on SESI, you know you want to! 8-)
> Louis
>> we have implemented a nice rig system now with preBlendshapes, 
>> wiredeformer, then a deformSOP. when used correctly it is very nice 
>> to control the deformation and still give the animators the freedom. 
>> Thing is it can be slow. I know about the assume coordinate changes 
>> toggles (blend and deform), the morph mode in the blendSOP etc.  The 
>> blendSOP will cook only those inputs with values above 0, but you 
>> still pay the price for numbers here and you are bound to get 
>> multiple floats in there somewhere. the morph mode helps since only 
>> the deltas are stored in the editSOPs once the file has been saved 
>> after you toggle it on and reload the file, so the memory hit is 
>> less. The wire deformer isn't optimized with the assume coordinate 
>> changes so that isn't much help either.  the difference in attributes 
>> also can be a pain as well, but you deal with it.
>> I haven't played enough with the metaball system yet to know if it is 
>> potentially easier to get more out of the rig. I saw the videos Calin 
>> put out. It looked great, but I was worried about the workflow quirks 
>> you had to do to set it up.
>> -k
The only thing I found problematic with the metaball and muscle capture 
systems is that I wasn't able to just put in a couple of muscles on top 
of a rig that was done in the standard way. It was kinda all or nothing. 
Very sweet but a bit difficult to hack up. I haven't played with it in a 
little while now though..


>> Louis Dunlevy wrote:
>>> I'd be curious to see what people think of this idea of a "relative" 
>>> deform for Houdini bones/metaballs. Any takers?
>>> Cheers
>>> Louis
>>> Louis Dunlevy wrote:
>>>> I was going to suggest the spreadsheet but you're there already I 
>>>> see. A bit messy though. I quite like the sliders on the bones too.
>>>> For facial rigs have you had any joy with the Morph tool giving it 
>>>> a rest position? When you hit the "Save Deltas" button it will do 
>>>> an Attribute Orient style deform based on what you've done in your 
>>>> edit SOP. I'm sure you're already aware but just in case..
>>>> I really would like to see a new type of bone behaviour like the 
>>>> "relative" mode in Maya's cluster deformer. That lets you throw in 
>>>> tons of extra deformers that have no affect whatsoever until their 
>>>> transform channels have changed. I find the problem with Houdini's 
>>>> bones is that they *always* have an effect on the geometry whether 
>>>> you like it or not. I think it's a big issue for facial rigs and 
>>>> secondary deformers.

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