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Xna animation without using skinned model example?

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6 replies to this topic

#1 mr.runner   Members   


Posted 16 March 2013 - 10:47 AM

The project I choose is a game where robots could fight. I have done all the job at importing models in my XNA game, but I am having difficulty playing a FBX animation. I could use skinned model example from microsoft website,but the problem is, my FBX file does not contain joints (skeleton). Arms, legs and head are controlled in the way of rotating at pivot centre (you can see how it looks in the bottom pictures).

PICTURES: http://postimage.org/image/7gnns9sz7/

My question is:"How can I change skinned model example, so that would play FBX animation without my model containing skeleton?" or "Is this even possible?"

Edited by mr.runner, 17 March 2013 - 08:47 AM.

#2 Steve_Segreto   Members   


Posted 17 March 2013 - 12:03 PM

Rephrase the problem to how can I turn my pivot centre's into joints to form a skeleton. I assume you are making a game where the player has to carefully control each pivot of his robot to get it to perform actions like walking and fighting?


Anyway, your pivot centre's are just the same as a bone or joint in a skeleton. I think the only difference might be that you do not wish for vertex skinning to happen based on them?

#3 mr.runner   Members   


Posted 19 March 2013 - 09:31 AM

My problem is not rotating objects, but playing animation. Maybe I don't understand or maybe I didn't explained the problem correctly.

Let's say that we have a box and that we would like to extrude every 6 faces. But we would like to extrude them from 0 seconds to 10 seconds (slowly extruding). This would be our *fbx animation.


And my question is:  "How can I play that animation, if the animation doesn't contain skeleton?"



 PS: Extruding box is just an example.  

Edited by mr.runner, 19 March 2013 - 09:31 AM.

#4 belfegor   Members   


Posted 19 March 2013 - 10:17 AM

I am not the best person to explain this but 'm gonna try.

If for example you have animation that lasts 10 seconds you could set 10 animation keys/sequences as one for each second, then for each key you have each vertex at certain position and/or orientation. Then you move your animation track "cursor" over time and interpolate position/orientation of each vertex to make animation going.


vertex1 xy(30,10)      xy(40,10)     xy(50,20) ....
vertex2 xy(10,10)      xy(20,10)     xy(30,20) ....
vertex3 xy(10,10)      xy(10,10)     xy(10,10) ....


// for each vertex
cursor.time += deltaTime * animSpeed;
cursor.time = fmod(cursor.time, 10s);
float lerpTime = (cursor.time - key[keyInx].time) / (key[keyInx +1].time - key[keyInx].time); // 0 - 1
CurrentVertexPos = lerp( key[keyInx].xy, key[keyInx+1].xy, lerpTime );

#5 mr.runner   Members   


Posted 20 March 2013 - 07:23 AM

Ok. I think I understand what you mean. But how could I change skinning model example from Microsoft for working the same way but with the difference that my model would not contain skeleton?


PS: I am new to XNA so please don't be angry if I missed the point. 

#6 CC Ricers   Members   


Posted 20 March 2013 - 11:01 AM

Skeletons in a model are essentially a collection of special mesh deformations, which influence an object based on vertex weights you give the model during its creation. Since your model does not use a skeleton, it does not have vertex weights so it cannot be skinned in the way you would expect.


Robots (and other mechanical objects) need matrix transformations that are only local to specific parts of a mesh, and it's ideal to export your model into a group of meshes, one for each pivot sphere, limb, etc. Then you can apply movement to the parts individually.


Here's an example of a tank with animated parts in a more rigid fashion. Each part is a separate mesh and has a bone matrix transformation applied locally to move each part. You animate the bones not in the way a skinned model would, but with rigid transforms over a hierarchy of parts.

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#7 mr.runner   Members   


Posted 20 March 2013 - 11:32 AM

Thank you all for answering so quickly.

So just to make sure, if I understand last reply. I cannot really play animation from *fbx without skeleton. But I can rotate parts of the 3D model, so it will look like playing animation (something like that is used in example you gave it). But if I do rotating (or scaling or moving) in code, wouldn't than be animating (in code) the "walk" pretty hard.


I mean you would have to rotate multiple parts, for having natural "walking" cycle. Walk cycle would be much easier to create in autodesk maya  than writting code.

Example what I mean with walk cycle:


Edited by mr.runner, 21 March 2013 - 01:36 PM.

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