Re: [Algorithms] Representing Animation Key Frame with Quaternion + Translation Vector

[Cedric P. <mor...@pl...>]

Hi,
I was just curious if it's used mostly or not, and why.

Cedric

Jason Hughes wrote:
> Cedric,
>
> For what it's worth, it's the only way to do hardware skinning on one 
> of the current gen consoles.  I'll give you three guesses which.
>
> Yes, it works.  But it also means that if you want to shift skinning 
> over to the GPU, you have to do it in several times the number of 
> batches, because you explode the number of matrices requires (because 
> they're a combination of ALL the weights and ALL the bone matrix 
> requirements for a whole vertex).  For a last-gen game with relatively 
> few verts and relatively few matrices, it's probably a good trade 
> off.  If your game has 200+ bones and several thousand verts and 
> allows for >3 bone skinning per vertex, you may be looking at close to 
> half as many matrices as you have vertices, depending on how your art 
> is generated.  The artist has almost no feel for how many matrices 
> they're effectively creating given standard tools at their disposal, 
> as well.
>
> But there's nothing wrong with it, if it works for you.
>
> JH
>
> Cedric Pinson wrote:
>> Hi,
>> Interesting topic, i am currently doing skinning and i would like to 
>> have some other point of views. I use similar technique from 
>> http://www.intel.com/cd/ids/developer/asmo-na/eng/172124.htm
>> 1 - in the pre process i identify set of vertex by uniq transform set 
>> (eg v0 v1 and v2 are transformed by bone1 and bone2 with the weight1 and 
>> weight2).
>>
>> 2 - Then i have a flaten list of transform by vertex group to update 
>> each frame eg:
>> so to have the final transform (in animation space) for the set of 
>> vertex ( v0, v1,v2) i have to collapse ( transform bone1 * w1 + 
>> transform bone2 *w2)
>>
>> 3 - Then in cpu or gpu i have to do only one matrix * the vertex. 
>> Because previous work computed the concatenation of matrix, it reduces 
>> the number of matrix needed in the vertex shader.
>>
>> the method is describe here,
>> http://www.intel.com/cd/ids/developer/asmo-na/eng/172124.htm
>> What do you think about that ?
>>
>> Cedric
>>
>> Jon Watte wrote:
>>   
>>> Lim Sin Chian wrote:
>>>   
>>>     
>>>> Just wondering if anyone has done this before and whether it is really 
>>>> better in terms of performance and accuracy.
>>>>     
>>>>       
>>> I'm under the impression that everybody does that. Not only does it save 
>>> space (assuming you don't need scale), but it also interpolates much 
>>> better. Interpolating between two frames with a matrix looks pretty 
>>> crufty. The only thing to watch out for is to make sure you go the 
>>> "short way" around -- dot product the two quaternions, and if the 
>>> outcome is negative, negate all the values of the destination.
>>>
>>> To compose quaternions, you just multiply them. Because it's a 
>>> rotation-translation pair, if it's parent relative, then you apply the 
>>> parent rotation to the child translation, and then apply your own 
>>> rotation around that point.
>>>
>>> Sincerely,
>>>
>>> jw
>>>
>>>
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>>
>>   
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+33 (0) 6 63 20 03 56  Cedric Pinson mailto:mor...@pl... http://www.plopbyte.net