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Model animation - too many calculations

Milcho Penchev · 2011-02-04T17:52:41

Well, I've been working on animating a model based on a skeleton. I have a half-assed algorithm that auto-attaches vertecies to bones. Each vertex is attached to anywhere from 1 to 3 bones. Each bone attachment also has an associated weight. The problem is then with animating the model. I'm using a low-polygon model - something like 760 faces, with less than 2000 vertecies. I then have to calculate the new position of each vertex based on it's bone attachment. For each bone, this consists of 3 multiplications, type double, to rotate to the correct position, 3 additions, again for doubles, to translate it to the correct position, and then a multiplication of that whole result by the weight assigned to that bone. At the end, I simply add up all the results for each bone, to get the new position. The above method works, assuming the attachments are correct. The problem is that it seems to take TOO long to compute that for all vertecies. I split the calculation up in 4 parts, where each update event it does 1/4th of the vertecies, and then updates only after all of them are calculated. That allowed me a bit over 60fps, but considering I'm only drawing one low poly model, that framerate is unacceptable. (For comparison, without calculating the vertex positions, I get framerate of 900+). I'm not sure where to optimize the calculations. They're all done on the CPU, which is a pretty big bottleneck, but I can't figure out how, if at all possible, to use the the GPU for that. Anyone have any experience programming model animation? Perhaps animating a model from a skeleton from an existing animation format? Any help at all would be greatly appreciated.

General and Gameplay Programming Programming

Started by MilchoPenchev February 04, 2011 12:44 PM

11 comments, last by Buckeye 13 years, 3 months ago

MilchoPenchev

1,178

Author

February 04, 2011 03:58 PM

Debug compiles (depending on what API you're using) usually link in debug (vs. release) libraries. Those debug libraries commonly do a lot of error-checking ( that's what "debug" does for a living ) - looking for unitialized variables, array indices out of bounds, etc., etc. Your experience isn't necessarily out of the ordinary. E.g., I get ratios of 200-400 ( 180mS vs. 0.7mS for one of my routines comes to mind ) between debug and release execution times.

Yeah, I knew debug does a lot for checking for errors, hence why I usually run in debug mode when debugging (actually, I've noticed you can't rely on the debugger in release mode). I've just never had such a huge gap in performance, until now. That'll teach me to post on here with questions that could've been resolved by two mouse clicks. =)

MilchoPenchev

1,178

Author

February 04, 2011 04:33 PM

Actually, since I'm not testing with a higher polygon count, does anyone know what a low- to medium- acceptable polygon count is for a human model? I'm no modeler, but I can just use subdivision to create a higher-resolution model to test.

Buckeye

10,754

February 04, 2011 05:52 PM

I don't know about "acceptable," but something a bit more complete than what you have in your posted image: maybe on the order of 2000-4000 faces (triangles), about as many vertices.

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

Model animation - too many calculations

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