Gravity around object

[Sakru]

Hi guys! I having trouble with putting a gravity force inside a object. For example you have a planetoid, and you want to land on it when you have gravity set to 0 in space but have the gravity around the object? How could i achieve this? I tried to make a trigger on top of planetoid, but when i run i always run like on a platform ( i fly away ), and not on the round surface of the planetoid.

[nick.ace]

You can do this, but you have to update this for every entity.

 

To determine the force that must be applied:

http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation#Modern_form

 

This equation would give you F (the magnitude of the gravity). You can probably just make up a G value though. The direction of F would be just towards the center of the planet. r is just the distance between the center of the planet and the object

 

Then you need to calculate the unit vector of F (I'll call it F_u):

http://www.vitutor.com/geometry/vectors/3d_vectors.html

 

Anyway, once you calculate F and the unit vector F_u, here is some pseudocode that should be close to the real implementation:

 

function Script:UpdatePhysics()

pos=self.entity:GetPosition(true) --position of object
pos_p=planet_entity:GetPosition(true) --position of planet

r=pos:DistanceToPoint(pos_p) --Calculate distance to the planet

F=G*(planet_mass*self.entity:GetMass())/(math.pow(r,2)) --Calculate the strength of the gravity

F_u_magnitude=math.abs(pos.x-pos_p.x)+math.abs(pos.y-pos_p.y)+math.abs(pos.z-pos_p.z)
F_u=Vec3(pos-pos_p)/F_u_magnitude

self.entity:AddForce(F_u.x*F, F_u.y*F, F_u.z*F) --This is the simulated gravity effect
...

end

 

 

I haven't tested this code, but this should in theory work.

 

A few notes:

• Gravity should be disabled
  
• The character controller will not work with this method since it's a custom physics object that relies on real-life gravity
  

 

Hope this helps!