View Full Version : Bullet dynamics calculation speed?

09-09-2014, 08:57 PM
I've recently started some basic animation following Tom Roth's Principles of Character Animation. It is a good tutorial and I have done all the figure animation for an initial walk cycle, but I'm attempting to get bullet dynamics and fibre fx to work with it all.

I couldn't find anything to have bullet dynamics calculate before frame 0 so I can keep my animation from frame 1 through 25. Instead I moved all the animation key frames up 40 frames to allow hair guides to relax, and everything works fine up to that. When the animation starts with a simple walk cycle, the hair, scalp, collision objects all move with the figure but the hair guides seem like they are moving through a fluid so by the end of the walk the hair is pulled back instead of resting on shoulders. There is also a span of about 10 frames where the figure turns from the front to the left side before the walk where the hair guides go crazy. It all seems like the dynamics don't calculate fast enough.

I re-read the manual on bullet dynamics, the properties, and what they do. I've fiddled with various values for the properties that sounded promising. Time scale I'm sure has a purpose, but nothing that I can see at the moment. Dynamics framerate sounded promising but ultimately didn't solve my problem (although it did help a little with the craziness in hair guides during the turn). I also added space between my walk's keys by doing the scaling in the scene editor, although I'm not sure if I did enough scaling.

I must be missing something. All help is appreciated.

09-10-2014, 02:26 AM
No you're not. LW's Bullet is a very basic implementation, with a very unfriendly user interface. It really needs work.

09-10-2014, 01:35 PM
Actually I think I found what I'm looking for... maybe. At least I've gotten it closer. I had render globals set with 30 fps which looks like bullet dynamics uses to calculate time between frames. I scaled my frames 4x then changed the fps from 30 to 15 and the combination seems to be working a bit better now.

It still seems like something else is missing, though. Now at 15 fps and a walk cycle that takes 50 frames is a little over 3 seconds for 2 steps.... hmm, maybe that's right. I'll have to start paying more attention to how fast legs move when people walk.