Brecht Van Lommel schrieb: > Hi Jens, > > On Tue, May 18, 2010 at 11:45 PM, bjornmose <[email protected]> wrote: > >> I don't know too much about Daniels implementation of the ODE solver. >> But in general: >> GC is known to find a local minimum if: >> >> <snip> >> >> I hope i could give some hints. >> If I was not clear enough, don't hesitate to ask. >> Some times I assume 'simple facts' to be known, ignoring it took me 20+ >> years to sort it out :) >> > > I looked for larger distances, but on the instable frames, the forces > were no bigger than other frames, and the initial residual (Ax - b) > wasn't bigger either. So investigating the other values you suggested > may be a good idea. But at this point I'm happy the sim is now stable > for the scenes I've tested, and I'm hoping that I can just leave the > integrator code and focus on other problems. > > > There's two problems that I'm looking into, but would also appreciate > any ideas or help on these. > > Currently the scene Campbell posted seems to be simulating stable > without collision, and the hairs are going through her face. Collision > is reportedly problematic but I haven't tested it yet, is first thing > I will do tomorrow. Getting a smooth collision response is important > here, we don't need the hair to be right on the head, if it stays some > small distance that's fine, but no jittering. > Again i am not up to date .. But last observations were collision is done asynchronous. Says unlike SB solver where collision is handled as force, cloth do a 'ad hoc' move out . Leads to 'spikes' the solver has to handle .. shut up here:)
> The second problem, that is actually multiple problems, is that we > can't get the forces right so that the hair is both moving enough when > it supposed to while still preserving the original shape when it's > hardly moving. To preserve the original shape we need to push up > pin/goal stiffness, damping, etc, which kills all the interesting > motion. If we don't the hair starts losing shape, which is clearly > weird for a nearly still shot. For more dynamic sequences when we > lower those parameters, when the hair comes to rest again it has lost > it's shape and is just hanging down straight along the z-axis (also > visible in the trailer when the little dragon is grabbed). > I don't know .. but feel But, check if cloth code really cares for painted pinning .. Last time i checked it was 1..0 ... in SB terms either goal 1.0 or 0.0 but no blending. Rather guessing than knowing, though. > It's simple to test, just run the sim with sintel in armature rest > pose, in the provided scene, her hair starts losing to gravity. > Tweaking hair weights and parameters can give acceptable results for > different scenes, and this is what we may end up doing (and are > already doing), but I would like to get it to do the right thing more > often. > > One way to look at it is that the hair shape sintel has now is > actually not the right rest pose, but is what we want as the > equilibrium when gravity is acting on it. So here the rest pose for > the sim should be such that when we run the sim her hair starts > falling down into the shape that was specified. Not sure if we can > actually do anything in practice with that insight, or if that > mismatch is really at the core of the issue. Another idea is to make > the pin/goal forces work a bit different, so that they get activated > more when the hair is moving less or nearer to the rest shape. > > Also, bending forces are really not working well, the extra springs > between every other hair vertex have multiple solutions and can push > the hair into incorrect shapes once it flips. Ideally angular springs > would be used, but they seem too complicated to implement in a > reasonable time. I guess the goal forces will just have to compensate > for them, or perhaps there's some tweaks possible to get them a bit > better. > > Thanks, > Brecht. > _______________________________________________ > Bf-committers mailing list > [email protected] > http://lists.blender.org/mailman/listinfo/bf-committers > > _______________________________________________ Bf-committers mailing list [email protected] http://lists.blender.org/mailman/listinfo/bf-committers
