3d pdf animation

was looking into adding animation to my 3d pdf objects again. it's really hard to find any useful info on the newer prc format (the best i could find was a low level adobe tech support guy whining about the iso application taking a long time). u3d has at least some skin and bone based animation, beyond the rigid body + scale part-level animation that is useless to me (every reference to key frame animation, afaik, refers to this). but i'm not sure if acrobat or the adobe reader support that part of the u3d ecma standard. this page (google cache) from right hemisphere seems to say that it doesn't, but that might refer just to their deep exploration code. at any rate, i think they were one of the founding parties to the standard, so it's not promising if they never bothered. somewhere i found an unreferenced statement that everything supports ecma 1st edition, but acroread 7 doesn't support ecma 3rd edition.

however, the JavaScript for Acrobat 3D Annotations API Reference doc on the adobe website describes a Bone object and specifically says it 'is usually moved over time to create animated characters.' Mesh objects contain geometry, but nothing in the api doc looks like it could be actual vertex positions, unless they're lurking in the Node.metadataString. i can find no additional info on Bone.

the U3D Supported Elements doc from the 3d dev center states that skeleton descriptions are 'parsed and unused (that is, no skeletal animation, skinning, or bones)'

also, opacity and material color animation are not supported, and i'm pretty sure that's a basic u3d limitation.

it's hard to find much info about the newer prc format. i don't see anything in the adobe spec docs that obviously provides for it (though not much anything obvious in the specs... quite sparse). i think the best i can do right now is look at the asymptote code (there was a passing reference to animating the prc in one of their journal articles as a todo item; alas, the only animation they show in that article is an ordinary movie). rumor has it that adobe turned the prc implementation over to a third party, bailing again on a drive into the 3d market, so i'm not sure prc has a future any brighter than u3d, which they have said (fwiw) they will always support.

so the only way out i can see right now is to create multiple meshes, one for each time step, and use javascript to cycle the visibility toggles. i guess the only real wasted space comes from the redundant connectivity, and that might be manageable if i continue to use only the exterior surfaces. and it would allow me to circumvent the u3d material color animation limitation. a rough estimate is 6.5 bytes/exterior node for u3d file size. actually, maybe that's not too bad... a 5 second, 20 fps animation with 8000 exterior nodes would fit in under 5MB. not too big for a short report or presentation. (maybe ~10 fps is a more realistic limit on what acroread can achieve.)

a little playing around with the quality options: diffuse color quality moved down from 300 to 100, -dcq 100, make practically no difference in file size. specular color quality, -spq 100, and animation quality 1000 -> 100, -aq 100, made zero difference since i'm not using either. geometry default quality down from 300 to 100, -gq 100, makes no difference, as does texture quality 75 -> 50, -tq 50. texture coordinate quality 300 to 100, -tcq 100, and normal quality 300 to 100, -nq 100, make zero difference. the one thing that does change the file size significantly is position quality. i had been using -pq 500, and -pq 100 decreases the size by about 7-8%. and maybe decreasing the palette from 256 to, say, 16 colors would help, though it would surely be less than a 10% difference. so i don't think there's any way i could squeeze it down more than 20-25%.