15 ms·

As long as you have near-cusps rather than real cusps (and to be fair: real planar cusps in 3D are easily avoid by just forcing planar curves to be non-planar d

As long as you have near-cusps rather than real cusps (and to be fair: real planar cusps in 3D are easily avoid by just forcing planar curves to be non-planar during your pre-render pass) simply drastically decreasing the sampling interval over low-radius-of-curvature sections is a perfectly valid approach. It's fast (ish =D) and gets the job done.

dahart 8y ago
I tried much smaller steps, and it never got me there with a reasonable step size. It was a lot less expensive to do adaptive sampling than crank up the step size. Plus, you already know, there’s no guarantee with regular sampling. Near cusps can be arbitrarily small. Production wanted a guarantee, even if things were to run slower. I think adaptive was faster, but their primary concern was to know they wouldn’t have surprises or have to call in support once there were hundreds of hair shots in the pipe. The other advantage of maximum angle sampling is when calculating arc length of a curve with piecewise approximation. Anyway, It’s entirely possible that seeing as many very near cusps as we did was because our physics simulation was under constrained or not very good. ;) But for whatever reason, my experience left me with the feeling that they’re common enough to be a serious concern, rather than rare and easily avoidable...
- TheRealPomax 8y ago
  Absolutely, when dollars are on the line, the procedure is always 1: make it work. 2: make it fast. 3: make it nice and write a paper on it. And while step 2 is sometimes optional, step 3 _always_ is =) If you run into cusps a lot on a hair simulation, that feels like evidence of a bad model, but plenty of good things have been done with bad models so that's hardly an indictment on the process. If your model yields loads of cusps, you need a solution, and this type of RMF is probably a very expensive solution.

dahart 8y ago

I tried much smaller steps, and it never got me there with a reasonable step size. It was a lot less expensive to do adaptive sampling than crank up the step size. Plus, you already know, there’s no guarantee with regular sampling. Near cusps can be arbitrarily small. Production wanted a guarantee, even if things were to run slower. I think adaptive was faster, but their primary concern was to know they wouldn’t have surprises or have to call in support once there were hundreds of hair shots in the pipe. The other advantage of maximum angle sampling is when calculating arc length of a curve with piecewise approximation. Anyway, It’s entirely possible that seeing as many very near cusps as we did was because our physics simulation was under constrained or not very good. ;) But for whatever reason, my experience left me with the feeling that they’re common enough to be a serious concern, rather than rare and easily avoidable...

TheRealPomax 8y ago
Absolutely, when dollars are on the line, the procedure is always 1: make it work. 2: make it fast. 3: make it nice and write a paper on it. And while step 2 is sometimes optional, step 3 _always_ is =) If you run into cusps a lot on a hair simulation, that feels like evidence of a bad model, but plenty of good things have been done with bad models so that's hardly an indictment on the process. If your model yields loads of cusps, you need a solution, and this type of RMF is probably a very expensive solution.