bone matrices in 3d formats...

Joakim Pdelski · 2011-04-23T17:08:42

I'm making a Blender importer/addon for a game format we're using. The format uses 4x4 inverse transform matrices for bones. I'm very puzzled because when I import the bones to Blender, or load the file in our game engine, the bone rotations seem way off. Here are some screens: www.postimage.org/image/258d8jh8k/ www.postimage.org/image/25889xfr8/ www.postimage.org/image/2584yuqro/ I'm sure most of you will agree that these rotations don't make any sense. Its not very likely that the 3d artists made the bones like that. The only explanation is that some 3d modellers store matrices in a different way or something. I tried to do the same with Blender. Seems correct: www.postimage.org/image/252j7aeis/ www.postimage.org/image/2536ct9fo/ (note that the bones aren't connected in any of the images, because the 3d formats dont store real bones per se, only transform matrices and the scale value in the matrix is not used for the lenght of the bone (it's always 1.0) I then tried to import other formats in Blender/3d engine and I got the same results. However, if I play the animations created for those 3d models, everything looks exactly as it should. So this means I'm not doing anything wrong during import, because the animations would screw up if the bones had wrong angles. What does this mean? Why should I care? This means that I can't make a proper importer for Blender, as those angles of bones would be unusable for modding. It also means if I hand edited the bone angles or just connected the bones, then the newly exported models wouldn't be campatible with the existing animation files. So I'm pretty stuck. I could post the importer and some sample files, but like I said it's also the case for other formats. Why is it like this? Is this some kind of conundrum or historycal meaning? Can something be done? this is the blender function for loading and creating the bones: def read_joint(index, file_object): # 64 byte matrix (16* 4byte float), 4x4, inverse data_chunk = file_object.read(64) rawlist = struct.unpack_from('<16f', data_chunk) # '<16f' = "little endian, 16* float (4 byte)" r0 = [[rawlist for i in range(el,el+4)] for el in range(0, 15, 4)] # create a Blender matrix bmat = Blender.Mathutils.Matrix(r0[0],r0[1],r0[2],r0[3]) bmat.invert() # inverts this matrix # You need to set this explicitly. skeleton.makeEditable() newBone = Blender.Armature.Editbone() newBone.matrix = bmat armature.update() heres an example skeleton with the weird bone angles, in blend format: www.megaupload.com/?d=H72YS2Q8

Graphics and GPU Programming Programming

Started by JoakimPdelski April 16, 2011 10:03 AM

25 comments, last by JoakimPdelski 13 years ago

JoakimPdelski

100

Author

April 21, 2011 04:43 AM

I forgot, I still don't know what can be done to the outmost bones, they don't have children to which they are connected, but they seem fine in your screenshot.

JoakimPdelski

100

Author

April 22, 2011 05:56 AM

bump....

JoakimPdelski

100

Author

April 23, 2011 05:25 AM

Yes! I just tested it and it's true. Thank you again. But Im afraid I still need to know how you handle the outmost bones?

KulSeran

3,272

April 23, 2011 08:50 AM

Yes! I just tested it and it's true. Thank you again. But Im afraid I still need to know how you handle the outmost bones?

There is nothing special about those, they are just attached to their parent as is.

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JoakimPdelski

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April 23, 2011 11:42 AM

but they seem fine in your screenshot. I have few dozen bones now that look weird. Did you maybe render the outmost bones as spheres to make it look so perfect?

KulSeran

3,272

April 23, 2011 04:22 PM

but they seem fine in your screenshot. I have few dozen bones now that look weird. Did you maybe render the outmost bones as spheres to make it look so perfect?

In my screenshot, yes, the bones are all spheres, with pyramids going from parent to child. Since the outermost bones don't have children, they don't have pyramids coming out of them. This could be just a Maya thing? But nothing special was done when I took this screenshot. Thats just the way it always looks.

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JoakimPdelski

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Author

April 23, 2011 05:08 PM

OK, it makes sense now, here at Blender you have a sphere for the base of the bone and a pyramid coming out of it which represents the bone's lenght and angle. So even if you have not connected any bones, the pyramid is still there, hence why it looks weird. Im afraid all bone shapes in Blender are like that, but as Blender supports custom bone shapes, I can just make a sphere and set some bones to render as one.

bone matrices in 3d formats...

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bone matrices in 3d formats...

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