Turn off or change gravity for individual objects?

[Azariel]

I was wondering if there was a way to change or turn off the gravitational forces applied to a specific object. Right now my janky solution is to change the object's mass, but when setting it to 0 it appears that collision detection no longer works (at least when both objects involved in a collision have 0 mass). Are there any better solutions out there?

[Guest]

This is tricky as the physics simulation is a whole system where all the actors live according to the same rules.

So changing gravity only for a specific object is kind of unsupported.

 

can you tell us what you try to achieve?

[Wingnut]

Hi guys.  Sorry to interrupt.  Testing playground:  https://www.babylonjs-playground.com/#15EUZJ#12

Ok, for THAT PG, line 70 is an "anti-gravity engine" for red sphere1. 

Lines 54-57 add mass to gray sphere2... after 8 seconds.

*shrug*  Red sphere CAN still have impact and recoil (restitution)... but Y-axis gravity-pull, is nulled/counter-acted.

 

On 9/15/2018 at 1:00 PM, Azariel said:

at least when both objects involved in a collision have 0 mass

Yep, this is true.  https://www.babylonjs-playground.com/#15EUZJ#15

In #15 PG...
- I have set a TINY amount of mass on red sphere (line 32).  I think it automatically rounds-up to .01 mass, so the line 72 anti-gravity line is still needed.  
- The gray sphere2 has no mass.  So, I must "pull" the gray sphere2 downward (to test collision with red sphere1).  Lines 73/74 do that.

Collision works, restitution/recoil works, but it HAS TO HAVE line 32 mass.  Remove line 32, activate line 31, and re-run... to test.

hmm.  Yep, when both physicsBody's have 0 mass... no colliding done.  Darn. 

Ok, now we got a playground for the forum's mad scientists to experiment-with. 

I think the direction of study will be... trying to teach the physics engine to ignore gravity on a "custom physicsBody". 

We will probably need to overload the Cannon "body" object with a boolean like ".ignoreGravity", and then teach Cannon how to watch-for bodies with .ignoreGravity = true, and then do special no-gravity processing for those collisions.  Erf.  Rough.  hmm. 

This would be a for-one-project hack, and not a core-level thing (unless you/we can convince @schteppe into supporting such a thing... in core CannonJS future versions).   Anyway, sorry for the interrupt.  Continuing with...

On 9/17/2018 at 10:58 AM, Deltakosh said:

can you tell us what you try to achieve?