How do you push a 'crate' in a locked directions?

[mdgunn]

Q: What's the best way to push objects (like a crate) around and have them lock to fixed directions?

 

E.g Push a 'crate' an undetermined distance along a path/paths but only allow it to move in fixed directions either 1 axis as if on a track or 2 axis ( e.g. 'crate' pushing puzzle).

 

I have something working (see below) but I don't think it's the best way to go.

 

Are there any example maps/code of pushing a crate around fixed tracks on a level. It seems like the sort of thing someone must have done but I've yet to see any examples.

 

The problem seems to break down like this:

 

1) Have an object to apply forces to (the 'crate') with a script to detect collision.

2) Detect the direction of push - currently faking this with 'trigger boxes' on the side. Maybe I need some trigonometry or something to work out the side of impact between the bodies?

3) Apply a force to the object limiting it's effect to a single axis (perhaps something in PhysicsUpdate?)

 

At the minute I have a working example where I can push a box in 1 direction using an invisible trigger box sticking out of it on the side I want the player to push from but I think this is probably not the best way to do it and am looking for someone who knows better!

 

function Script:Collision(entity, position, normal, speed)
--    System:Print("Collision speed = "..speed)    
--  Speed will be zero if 'trigger box' is a trigger as it needs mass 0 to avoid dropping down through floor/level.
--    if speed>self.threshhold then
       if self.entity:GetParent() ~= nil then
           local parent = self.entity:GetParent()
           parent:AddForce(0,0,200,true)    
       end
--    end
end

 

Thanks,

 

Michael

[Josh]

You could create a slider joint so it can only travel along a certain distance in one direction:

http://www.leadwerks.com/werkspace/page/api-reference/_/joint/jointslider-r737

[mdgunn]

Thanks Josh,

 

I had considered a joint slider. I checked out the docs and can see it is designed to limit movement in 1 direction but I wasn't sure if it was the best way to go for controlling crate movement in more than one axis.

 

Sounds like I would still need to detect which way I'm trying to push and then setup (or disable) slider joints to allow me to push only in the direction I'm trying.

 

I will take a deeper look.

 

Cheers

[mdgunn]

I've hacked away at the sliding door script to create a script that moves the attatched object away as you bump into it (well you actually bump into a trigger collider currently)

 

Problem is, it will only do it twice then stop.

 

I think maybe the slider joint is not actually resetting when I am trying to reset it and has reached it's limit so not resetting properly. I am trying to reset it each time a move completes but I think I don't understand either how the slider works, or the vector information it needs to alter it's position or something.

 

Can anyone take a look at the associated map and script and point out the probably obvious error?

 

NOTE: The script is a real hack job and not meant to be complete so please forgive the mess!

 

Here is a Dropbox link which I hope works OK. Unsure if I can link a file to this post.

 

https://www.dropbox.com/s/3ctogtsxjf239qh/PushAwayJoint.zip?dl=0

(contains map, script and screenshot)

If there's a better way to supply a package then please let me know.

 

Maybe I should try another way altogether?

 

Thanks,

 

Michael

[BluHornet]

What you could do is make the crate and then add invisible csg cubes around the crate and make them a child of the crate. Make a short script for each that when the crate is moved a set distance in a set direction from the player when used. you would need to set the direction and distance. something like when used take the crates position and add a set amount to the x and z coordinates of the crate then save that as a set position. then if the set position is not the current position move the current position closer. If I wanted to move "South" then I would change the set position to the current position's x value to the value -2. This is a good application for lerp (linear interpolation). Also some smoothing could make this better. One last thing if this is not done in update physics you will need a time factor for reliability.

 

[mdgunn]

Yeah the CSG 'trigger' cubes and manual intervention in the movement is the direction I was heading when I wondered if I was heading the right way, so it's reassuring that you seem to think it's a doable solution. Thanks for the extra pointers.

 

I felt sure someone had probably done a 'cube pusher' but so far someone that has completed such an implementation doesn't seem to have passed by yet.

 

Thanks for the help.