Pbd Tet Inversion
Currently none of FEM Pbd models work well with tet inversion which happens often at large timesteps for real time simulations. Only pbd volume+distance constraints can deal with it but those suffer other physical inaccuracies.
- Neo hookean becomes unstable as it approaches 0 in & inverts.
- StVK is the most stable but tets become stuck after inverted.
We'd either need a modified neo hookean or modified StVk (not shown above).
Fixed: MR #872
Edited by Jacob Moore