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+--- Thread: Slow values greater than zero - bug or feature? (/thread-862.html)
Slow values greater than zero - bug or feature? - insertmesh - 07-05-2019
I recently had a sim, where some cloth particles seemed to stop mid simulation and I figured out the cause.
I had a slow operator in the flow set to 10% and with default values otherwise to counteract some force with noise.
As I changed the "only affect" from "All values" to "Values greater than zero", that behaviour stopped.
I´m assuming this makes sense and I just don´t understand it, or is this a bug?
Could you elaborate?
Also, if this is how its supposed to be, it might be worth considering making "Values greater than zero" the default.
RE: Slow values greater than zero - bug or feature? - tyFlow - 07-06-2019
That setting is a filter for the vectors (velocity and spin) the Slow operator operates on.
Take for example velocity. If a particle is moving from left to right, it's velocity vector might be something like [1,0,0]. If Slow is set to "values greater than zero", and the amount is set to 50%, after 1 time step the Slow operator will change the velocity to [0.5, 0, 0] (vel.x * 50%, vel.y * 50%, vel.z * 50%). However, if the velocity is [-1, 0, 0] (ie, moving right to left), then after 1 time step the velocity will remain the same if Slow is set to affect values greater than zero, because vel.x (-1) is less than zero and so will be ignored by the Slow operator.
An example usage of this is if you have some particle that fly up in the air too high...instead of increasing the value of gravity or damping their overall velocity, you could simply apply some Slow to their velocity z-axis and set the mode to "values greater than zero". With that setup, damping will be applied as they move upwards, but not downwards, thereby allowing for greater control over their motion without changing other simulation parameters like the strength of gravity of their initial rate of acceleration.
It doesn't make sense to have the default mode be anything other than "all values", though. The "greater than" and "less than" modes are only useful in some situations.
RE: Slow values greater than zero - bug or feature? - insertmesh - 07-06-2019
Thanks for the explanation, makes sense now how to use that feature and to not change the defaults.
I still don´t understand though, why in my setup some cloth pieces get stuck, I´m assuming that some forces in the cloth op are counteracting the noise forces and through the slow operator they cancel each other out until their velocity is zero, so they get "stuck".
And by changing the slow operator to "Values greater than zero it simply wouldn´t dampen all values, thus keeping the cloth particles moving.
If you wanna see the problem in action, you can see it on this R&D I posted in the facebook group:
https://www.facebook.com/groups/2214906212107536/permalink/2237023826562441/
RE: Slow values greater than zero - bug or feature? - tyFlow - 07-08-2019
Could be that, depending on the scale of your scene, the Bind Solver sleep settings are kicking in. Try setting the sleep thresh to 0 and see if that changes anything.
RE: Slow values greater than zero - bug or feature? - insertmesh - 07-09-2019
Oh right, completely fogot that the particle bind solver also has sleep settings...thanks for the suggestion, I´ll try that.
(07-09-2019, 09:01 AM)insertmesh Wrote: Oh right, completely fogot that the particle bind solver also has sleep settings...thanks for the suggestion, I´ll try that.
Jep. All it took was to lower the Particle Bind solvers sleep velocity threshold...Thanks for pointing this out!