[SOLVED] applyLocalTorque in PlayCanvas

Gamer_Wael · November 13, 2020, 9:56am

Hi, I wanted to apply torque locally to my player. But PlayCanvas doesn’t seem to have an applyLocalTorque function. But it seems ammojs does support it.

github.com

kripken/ammo.js/blob/00506d296df957d80bd192d27ff8a3ef2aa9f176/bullet/src/BulletDynamics/Dynamics/btRigidBody.h#L319


		m_linearSleepingThreshold = linear;
		m_angularSleepingThreshold = angular;
	}

	void	applyTorque(const btVector3& torque)
	{
		m_totalTorque += torque*m_angularFactor;
	}

	// XXX AMMO local addition to bullet
	void	applyLocalTorque(const btVector3& torque)
	{
		m_totalTorque += m_worldTransform.getBasis() * torque * m_angularFactor;
	}
	
	void	applyForce(const btVector3& force, const btVector3& rel_pos) 
	{
		applyCentralForce(force);
		applyTorque(rel_pos.cross(force*m_linearFactor));
	}

I tried to understand how to call ammojs functions from PlayCanvas but I found it a bit complicated. This is what I used:
https://developer.playcanvas.com/en/user-manual/physics/calling-ammo/

I would appreciate it if anyone can help me figure this out.

Thanks.

Leonidas · November 13, 2020, 10:02am

Hi @Gamer_Wael,

I think that method is available in the internal Ammo.js body object, you can find a reference to it like this:

this.entity.rigidbody.body.applyLocalTorque(50,0,0);

Try it and let us know if that works.

Gamer_Wael · November 13, 2020, 10:08am

Thanks for the reply.

Unfortunately, it doesn’t seem to be working.

This works fine:

this.player.rigidbody.applyTorque(0,0,5);

But this doesn’t:

this.player.rigidbody.body.applyLocalTorque(0,0,5);

yaustar · November 13, 2020, 10:52am

Chances are that it’s expecting an Ammo.btVector3 type.

Try:

this.player.rigidbody.body.applyLocalTorque(new Ammo.btVector3(0, 0, 5));

I recommend looking at the engine source for more examples on using Ammo directly: https://github.com/playcanvas/engine/blob/master/src/framework/components/rigid-body/component.js

A list of exposed functions are here: https://github.com/kripken/ammo.js/blob/master/ammo.idl

LeXXik · November 13, 2020, 10:58am

@yaustar I think that is the latest IDL. Is it used by Playcanvas? Is there a place where one may check the bindings of the Ammo version used by PC?

yaustar · November 13, 2020, 11:14am

Honestly, not sure which version we are tracking. If in doubt grab the latest from the Ammo repo.

LeXXik · November 13, 2020, 1:09pm

Right, unfortunately it is not as easy, because the version that is used by Playcanvas is using a special feature (Ammo.addFunction) which is not enabled in the default build, available in Ammo repository. One would need to download the sources, set up emscripten and build with a compilation flag that enables it.

yaustar · November 13, 2020, 1:53pm

@will Which version of Ammo are we using these days? AFAIK, we are not maintaining our own private fork.

will · November 13, 2020, 1:56pm

Correct. We just use the latest build directly from the master ammo.js repo maintained by kripken.

LeXXik · November 13, 2020, 2:01pm

@will @yaustar
Thank you for the response. So, I think the pre-built version in kripken’s repository is older than the latest IDL bindings file. Nevertheless, I downloaded the pre-built Ammo files from the build folder in the repository and added to Playcanvas project. Here is the result:
https://playcanvas.com/editor/scene/1032122

yaustar · November 13, 2020, 2:05pm

Project is private

LeXXik · November 13, 2020, 2:06pm

Fixed

yaustar · November 13, 2020, 2:12pm

Odd, looking at the commit history on Ammo, it should be there

LeXXik · November 13, 2020, 2:21pm

I think the way the callbacks are handled was changed. If you are referring to the addFunction commit for the test, then the test was changed: