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Skeletal animations and skinning


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#1 kumpaka   Members   -  Reputation: 100

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Posted 17 March 2012 - 02:06 PM

Hi there,

Ive been struggling with skeletal animation and skinning now, using this tutorial as reference:
http://content.gpwiki.org/index.php/OpenGL:Tutorials:Basic_Bones_System

I could get a lot of it to work, but now i started searching about how to skin... I is it possible to define an armature in blender, and also weight the vertex there and somehow use it in my opengl/c++ app? i can now build a skeleton, but i have no clue on how to load a model(obj?) and paint the vertex.

Thanks in advance.

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#2 JTippetts   Moderators   -  Reputation: 8652

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Posted 17 March 2012 - 04:32 PM

.OBJ doesn't support animation.

You'll probably want to look into other available formats for exporting animations from Blender. Possibilities include the DirectX .X format (which isn't DirectX specific, so is just fine for even OpenGL apps), Collada, Ogre's mesh formats, etc... Personally, I like the Ogre format. The unofficial Blender 2.6 exporter can be found here (the official exporter for 2.6 is still in progress) and it exports mesh and armature data to XML which can be processed to a binary format by Ogre's command-line tools, or which can be parsed by your own application instead.

The Ogre format supports up to 4 bone weights per vertex, though of course Blender supports many more. The exporter will choose the 4 largest weights and spit out a warning upon export, that can safely be ignored. You perform vertex weight painting in Blender itself; the vertex weight painting is fairly intuitive and easy to do.

There are many tutorials available for the actual acts of rigging the mesh with an armature, painting the vertex weights (Blender also provides a few options for automatically assigning weights based on bone envelopes) and parenting the armature to the mesh. Once this is complete, you can pass the mesh/armature assembly through the Ogre exporter to get the XML files.

The Ogre exporter will generate two files (well, 3, since it also outputs materials; if you are doing your own system rather than using Ogre, you can ignore the material export). One file defines the mesh, and specifies vertex data and bone weights per vertex. The other file defines the skeleton and the keyframes of the exported animations.

#3 kumpaka   Members   -  Reputation: 100

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Posted 17 March 2012 - 07:09 PM

I can do those things in blender, but then if i export to ogre, and then from ogre to xml, i can load and work with that in my opengl app? that sounds nice! if its a fixed animation i can even do it blender and proceed trough the same steps?

#4 JTippetts   Moderators   -  Reputation: 8652

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Posted 18 March 2012 - 11:16 AM

Yes, you can do all the skinning and animation in Blender, export to the Ogre format, then load in your app. Ogre also supports blending different animations together to support, for example, running+shooting, running+dodging, etc... types of scenarios.

Note that the Ogre format is just one possibility, but it is a well-supported format with an active community.

#5 kumpaka   Members   -  Reputation: 100

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Posted 19 March 2012 - 11:11 AM

I just tried exporting from blender but the armature doesnt show up, for what ive looked around it seems to be a problem with the root bone, did you have any problem like this in blender 2.6?

Thanks a lot for the help btw, finally feel like im moving forward.

#6 kumpaka   Members   -  Reputation: 100

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Posted 19 March 2012 - 04:19 PM

I used another model already with an armature not done by myself, but on this one i got the same error but it sucessfully exported the skeleton.xml
Heres the thing, on the structure of the mesh.xml theres something like this "<face v1="0" v2="1" v3="2"/>" that defines faces, i still dont know what indexes this values are since the vertex arent identified so im assuming its by the order they are red from the file.

When drawing, if i drawed every face as a single triangle it would turn out very heavy i think. If instead i made an algorithm to search in this list for faces that had 2 vertex's wich were the same as the last 2 drawn, i could use triangle strip and save a bit. Would this be bad? also when moving the skeleton according to each vertex weight, would it have a nasty effect using triangle strips? Thanks in advance.




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