Entity::GetForce()

[SpiderPig]

Similar to the newton function here I'd like to be able to get the amount of force applied to an entity in the last physics update.

Entity::GetForce() or maybe Entity::GetAppliedForce()?

I want to know what direction an object is being pulled - this is not always going to be the velocity.  An object can be stationary yet still have a large force acting on it.

[Josh]

Quote

This function is only effective when called from NewtonApplyForceAndTorque callback.

I think this is for processing forces right before they are applied.

Forces can be applied two ways:

• Collision
• Programmatic

In both cases, you have control over or access to the time that force is applied.

[SpiderPig]

I think your right.  So because there are two ways forces are applied it might not be possible for you to add a function that can get the applied force in last physics step?

[Josh]

Why would you need that, if you already have access to that information when it happens?

[SpiderPig]

 AddForce() could be called anywhere within the program, and how would I get the force applied by collision?  The Collide function in the components only has speed.

I need it for finding out the direction the object is being pulled in so I can align my player controller to gravity as it falls.

[SpiderPig]

This where a PhysicsUpdate() hook in the components or HOOK_PHYSICS_UPDATE would be great.  It could have an argument called force.

[Josh]

The collision includes the normal, which gives you the direction. I don't know how to get the "force" of a collision. This function does not:
https://github.com/mmozeiko/Squares3D-Android/blob/dc7002d3e638a9ed0ffd090dc52168029321cec7/jni/newton/coreLibrary_200/source/newton/Newton.cpp#L2095

[SpiderPig]

Perhaps something like this for tracking Entity::AddForce at least?  The total force (including collision force) can only be retrieved from with the callback like you said.  I more interested in knowing what the force is that is about to be applied to the physics object by code.

MyComponent {

virtual void PhysicsUpdateStart(float& applied_force_this_loop){
	applied_force_this_loop = 0.0f;  //Do what ever you want with the force that is about to be applied.
}
}


//Maybe it could track what is being added?
Entity::AddForce(Vec3 new_force){
	applied_force_this_loop += new_force
}

//Once the physics update has completed
End_PhysicsUpdate(){
	//All entiites force can be reset to zero
	applied_force_this_loop = 0;
}

PhysicsUpdateStart could even be called from the torqueandforce callback - if it's thread safe...

void callbackForceAndTorque(const NewtonBody* body)
{
	auto total_force_ready_to_apply = 0;
	NewtonBodyGetForce(body, total_force_ready_to_apply);

	auto componet = body->GetUserData();
	componet->PhysicsUpdateStart(total_force_ready_to_apply);
	NewtonBodyAddForce(body, total_force_ready_to_apply);
}

 

[Josh]

The documentation above says that the function will return zero if the two bodies are in motion, because the contact is not a force but an impulse. This is getting beyond my knowledge of physics. The best approximation I can think of is to take the normal and speed * speed of the collision times the other body's mass, and that's your kinetic energy, or "force".