how do i get a list of entities "in contact" with another?

[Charrua]

is there a function to get a list of entities that are above another, in contact, physically speaking.

 

When an entity collides another a collision is detected an i can test for collision but after a while stop bouncing and collision stops also. What i need is to know which entities remains in contact.

 

I can do a aabb test or keep track of entities that has been collided.. but all has its pros and cons, is there a physics way of testing entities actually in contact?

 

thanks

 

Juan

[Josh]

This is tricky because if an object is at rest, it theoretically is not in contact with anything. Otherwise it would experience a force pushing it away and would not be at rest.

 

The engine does not store lists of previous collisions because it would just be a lot of data that is mostly never used, and add a lot of complexity when entities are deleted.

 

There is a function to gather all entities in a bounding box, but what specifically are you trying to do with this? Maybe we can help.

[gamecreator]

The list seems like the way to go. I think you could just check if an entity collided with something the turn before and if it's at rest now, it's probably safe to assume it's still colliding.

[Charrua]

thxs

 

i'm implementing a "conveyer belt" (kind of) and it hast 3 states: forward, backward and stop

while in forward or backward any entity colliding with it is moved and as it is moved it remains colliding and so the belt woks as spected.

If i stop motion, then.. entities stop colliding the belt and then, when i need to restart movement, i need to know which entities remains over it.

Some entities may finish colliding because they reach the end or slide outside the belt (for any reason) so having a historic of entities collided (recently) is not a bad idea but isn't sure that this list is will be correct all the time.

 

One of my ideas was use an aabb and is still the one i guess will use but before i needed to ask .. just in case

 

here what i'm doing currently:

(the other cars will have other uses, forklift and the like)

having some spare time so i decided to enjoy a little.

 

https://dl.dropboxusercontent.com/u/78894295/leadwerks/conveyor%20belt%202.mp4

 

https://dl.dropboxusercontent.com/u/78894295/leadwerks/conveyor%20belt.mp4

 

@gamecreator, i was posting as you did your, the list is not a bad idea, but there will be no garanties, i mean, a box should be pushed away or lifted from one belt to other place and will, perhaps, remains in a list...

 

 

Juan

[Rick]

Maybe something like:

 

 

Box.lua

Script.entered = false
Script.exited = false
Script.hadCollision = false

function Script:Start()
self.collidedBelt = nil
end

function Script:UpdatePhysics()
   if self.entered then
       if self.hadCollision == false then
           if self.exited == false then
               self.exited = true
               self.entered = false

-- we aren't colliding with anything so we are either at rest (maybe) or falling
if self.collidedBelt ~= nil then
self.collidedBelt:RemoveItem(self)
self.collidedBelt = nil
end
           end
       end
   end

   self.hadCollision = false
end

function Script:Collision(entity, position, normal, speed)
   self.hadCollision = true

   if self.entered == false then
if entity.script ~= nil then
if entity.script.isBelt ~= nil then
self.collidedBelt = entity

-- add ourselves to the belt so it knows it has to push us around
entity.script:AddItem(self)
end
end
       self.entered = true
       self.exited = false
   end
end

[Charrua]

i'm at work now, i'll give it a try later, thanks

 

i was thinking belt side, you are thinking box side..

[Rick]

Yeah I figured the box can tell what it collided with so if it's a belt it tells the belt to add it to the belts list and when it stops being that specific belt it's able to tell that belt to remove it from its list. Things in games are almost always backwards from what you'd think in real life.

[Josh]

The best way to do this might be to create an invisible box above the belt. In the object's collision function, apply force to any object that collides with it. Use the trigger collision type so it acts like a force field.

 

You might be able to do this in the collision callback of the belt. When a collision occurs, try adding a force or adjusting the velocity of the colliding object.

 

If i stop motion, then.. entities stop colliding the belt and then, when i need to restart movement, i need to know which entities remains over it.

Get all entities in an AABB and add a force of (0,0,0) to each to wake them up.

[Charrua]

You might be able to do this in the collision callback of the belt. When a collision occurs, try adding a force or adjusting the velocity of the colliding object.

 

i'm basically doing it, but didn't figure out how to "wake up" entities over the belt when at rest.

 

this is my current belt's collision code:

 

function Script:Collision(entity, position, normal, speed)
--self.stateValue may be -1:backward, 0: stopped, 1:forward
--self.speed is a factor to adjust belt speed
if self.stateValue~=0 then
 rot=self.entity:GetRotation(true) --belt orientation
 vel=Vec3(0,0,0)
 vel.x = Math:Sin(rot.y)*self.stateValue*self.speed --get x,y components of orientation
 vel.z = Math:Cos(rot.y)*self.stateValue*self.speed
 entity:SetVelocity(vel) --applya velocity to entities that collide with the belt
end
end

 

guess now has some other ideas, apply a 0,0,0 force to wake up never cross my mind and the invisible trrigger thing.. have to give it a try also.. as always it's a matter of find a nice solution doing some tricks in between to get good results with few resources..

 

thanks again

 

Juan