Animated COLLADA files provide the following info Skin - bind shape matrix - list of joint/weight index pairs - list of weights - list of joint nodes used during skinning - list of inverse bind matrices, one per joint and the animation channel (track) data. Does the entire contents of this file make for a single animation? (lets assume there is only one animation in the file) is the skin info unique to this specific animation data, or is it unique to the model data? I read you can pre transform the model by the bind shape matrix because this will be the base pose for the entire animation. So does that mean for every animation you will have unique skin data (bind pose matrix, weights, inv bind matrix), animation data and a pre transformed mesh copy?

Yeah thats what I was wondering about, if i pre transform using the bind shape matrix for every animation (this was assuming each animation got its own set of skin data, with a different bind shape matrix) the copies of that mesh would balloon every time I need a new animation.

Quote:A single set of skin data can be animated with any number of animations.

This is what I figured at first its also what Im hoping. What Im trying to do is pull all the animation and character geometry from animated COLLADA files, and create a mesh and animation file from them, but Im trying to figure what data is constant across all animations and put that in the mesh file, and the animation data that changes per animation (walk, idle, run, etc) pull that out and drop it in an animation file, then bring it all together. One animated model file, and a bunch of animation files that target it. So any unique data that doesnt change, skeleton node hierarchy, mesh, joint name list, ends up in the mesh. Any data related to making him do an animation, goes into the animation file. So I have

Mesh File
------------------
Skeleton node hierarchy (joints)
Joint name list (referred to by index)containing joint transform data)
Mesh data (that get skinned/rendered)

Animation file
------------------
Single Animation (time data, name)
- containing channels
Multiple channels (track data? xform info for joints)
- target joint index
- interpolation type
- type of output values (quat, translation, scale)
- output values (xform data)

and the skin data which im unsure of where to place, because Im not an animator and Im unsure if this stuff would change per animation, or change partially

Skin data
- bind shape matrix (places him in T pose, is there one of these per animation?)
- list of nodes that are targeted
- inv bind matrix list (one per target node)
- weight list
- per vertex, joint/weight index pairs, or the number of influences per vertex

I guess when youre animating do you "set" a new bind pose at the start before animating? this would change the bind shape matrix, and the inv bind list and at least make those two unique to the animation. Meaning part of the skin info at least would end up in the animation file.

Im basing this all off what COLLADA throws at me so I get the feeling there is something I should be calculating/deriving from this data that isnt explicitly provided with respect to "poses". What Im doing right now is

- after loading the mesh, create a copy of it and transform each vertex position by the <bind_shape_matrix> (BSM) a 4x4 matrix (transform normal later when its working)

loaded mesh data (skinned and render)
loaded mesh data copy (pre transformed copy of loaded mesh by BSM)

Each frame with a running animation...
1) Update the Animation: Interpolate/build the joint animation xform data, apply it to the joint
2a) Update the joint hierarchy: creates jointWorld
2b) Update skinMatrix = jointWorld * jointInvBind
3) Update skin mesh: Using the pre transformed bind shape copy
For each vertex (from BSM copy)
- start with bsm_vertex
- For each vertex influence (joint/weight)
-- get joints skin matrix, get weight
-- out_vertex += (jointSkinMatrix * bsm_vertex) * weight
- store skinned out_vertex for rendering
Next vertex (from BSM copy)

this does perform the animation, but because the bind shape matrix is always the same T pose (character terminology, rest pose?) for every animation (walk, run idle), it seems that its influencing or biasing every animation towards this T pose, which would make sense seeing as its being used that way (start point for skinning), but it seems like it shouldnt. Which is where this idea of some sort of start "pose" per animation comes in, which I feel Im missing, and should be calculating some how. Or, a bind shape matrix per animation, something. Although it could be related to the way it was animated.

For ref sake, the weight data looks odd but that because his parts are not joined, Rayman like

In your first example where would "animMatrix" come from? What would it be? How is it calculated?

From the COLLADA spec BSM is... which I assumed to be the first matrix you apply to the mesh vertices every frame, regardless, so do it once and store a copy of the original mesh with it applied



where:
n: number of joints that influence vertex v
BSM: bind shape matrix
IBMi: inverse bind matrix of joint i
JMi: joint matrix of joint i
JW: joint weight/influence of joint i on vertex v
Common optimizations include:
(v * BSM) is calculated and stored at load time.

Yes. The result of the interpolation is stored as the joints local xform, once all interpolating is done and the local is set for each joint, the world matrix is calculated from the parents of each joint (JM from the img, which i have referred to has jointWorld, which I think is your animMatrix).

Quote:I'm guessing that BSM may just be a transform for the base pose mesh.

Yes. I must have the Bind shape matrix applied to my vertices first or my geometry explodes and arms and legs end up everywhere.