Low Gravity

[marwie]

Hello,

is it possible to set a body to zero gravity (e.g. to behave like in outer space) without having to change the gravity of the whole physics world?

[SuboptimalEng]

I'm curious about this as well. A simple fix would be to run applyForce in the animate function.

body.applyForce(
  new CANNON.Vec3(0, 10, 0),  // force (not gravity)
  new CANNON.Vec3(0, 0, 0)   
)

[marwie]

@SuboptimalEng you mean to counter gravity?

Id rather not, if there is no option yet maybe it can be added as it should be rather simple

[SuboptimalEng]

Just jumped into the code to see what you meant. If I understand it correctly, a better option could be to add body.type like ZERO_GRAVITY and update the internalStep function to handle it.

https://github.com/pmndrs/cannon-es/blob/master/src/world/World.ts#L539-L551

I'm super new to this btw. Started learning Cannon.js + game dev physics two days ago.

[marcofugaro]

Hey! To make only an object appear gravitless, you have to apply an equal and opposite force to the object before each step.

const world = new CANNON.World()
world.gravity.set(0, -9.81, 0)

const body = ...

world.addEventListener('preStep', () => {
  body.applyForce(new CANNON.Vec3(0, 9.81, 0)) // opposite of gravity 
})

[marwie]

what do you think about instead having to loop through a set of bodies marked as using gravity just skipping them in core (via some flag as @SuboptimalEng suggested) ?

[marcofugaro]

It is not recommended as body types are only three in phisics engines. You can patch it yourself but cannon-es won't add support for it.

[marwie]

I see, thanks (just asking because Unity has the option and we are exporting to threejs so im looking into how to translate that setting)