Multiple gravity sources

[xtreampb]

Other than me doing constant gravity tests in my code, is there a way to set 2 objects to have a gravitational pull and which ever object i'm closer to, i will begin to 'fall' towards?

[Josh]

Internally, the gravity value is just a force added to each active body. So if you have more complex logic like your describe, adding the force you want would be the only way.

[xtreampb]

just so that i know how it is done calculated. I'm assuming that you are using the setforce function and applying it to the negative y axis. Is that value being increased every second? what is the equation you are using if you don't mind me asking?

[Josh]

It just calls AddForce(gravity) where gravity by default is 0,-9.8,0 times mass:

Vec3 force = (spaceship->GetPosition(true) - planet->GetPosition(true)) * spaceship->GetMass();
spaceship->AddForce(force);

 

Technically, gravity increases as you get closer to an object though, so it should really be something like this:

Vec3 force = (spaceship->GetPosition(true) - planet->GetPosition(true)) * spaceship->GetMass();
const float gravityrange = 100;
force *= 1.0 - min(force.Length() / gravityrange,1.0);
spaceship->AddForce(force);

 

If you do this in the UpdatePhysics callback or script function, it will only get called for active bodies, and it will be called once per physics update.

 

Fun physics fact: See how I multiplied the force by the object's mass? That's the reason a piano and a walnut will fall at the same speed (not counting wind resistance).

[xtreampb]

I could be loosing my mind but was is the min function that you call, and what is 'the magnitude' of a vector.

[Josh]

Magnitude = length.

 

The min function is a C++ built-in thing. I think in Lua there is math.min or you can just call the Leadwerks command Math::Min().