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What does it happen when importing a character and assigning it another skeleton ?

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    What does it happen when importing a character and assigning it another skeleton ?


    It's not a question about an issue but about to understand what it happens exactly when importing a character and assigning it another skeleton. Let me explain more concretely :

    I've imported a character and given him another skeleton in order to animate him. The given skeleton is the Advanced Locomotion System Mannequin skeleton : See picture 1 below.

    I made very short arms to my character just to see what UE gonna do... I was pretty sure that my character would be stretched because the arms mesh will follow the skeleton that I assigned to the character (which is longer), since I didn't retarget the skeleton neither the animations. I was pretty sure that the arms will follow the arms' bones of the ALS_mannequin.

    Though, it's like UE did a retarget while I DIDN'T retarget NOTHING ! I just selected the ALS_Mannequin_Skeleton then click on ALS_AnimBP in the Mesh BP > Skeletal Mesh > Post Process Anim Blueprint, here : See picture 2.

    Finally, I selected my character's mesh in the viewport of the ALS_Mannequin BP class... Here is the result once I did this :

    In the first gif, you can see my character mesh and his skeleton in one tab, then his "active skeleton" (if I understand the thing well...) in another tab, with the ALS_mannequin blue mesh. Then when I play, you can see the arms (and the entire character, I presume...) have been like automatically retargeted... But I repeat : I didn't retarget nothing !

    So... Does UE make some kind of "auto-retarget" when giving to a character another skeleton than his proper base skeleton during the import ? And so it's useless to do some retarget with the "traditionnaly way" (right click on the Anim BP or an animation asset and click "Retarget...") ? I'd like to understand what UE does exactly when I give another skeleton to my character because it's intrigues me very much... I'm rather confused...
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    Last edited by Jorickan; 07-30-2020, 09:52 PM.

    By default, most bones on the *default* skeletons are set with Retargeting Skeleton option enabled.
    What that does is it eliminates all translations from the animation, so things have the potential of looking wrong when translations of the bone chains are needed (maybe you do stretch limbs animations and similar).

    Additionally, if you sculpted and weight-painted the object/character in a similar base position/pose, then you would not need to re-target anything to get it to work. The problems/issues come in when you decide to use completely different skeletal structures and positions.

    Aside from that, you do know that a double negative means you did indeed retarget stuff right? :P