Changes to water and collisions

We are fixing two small bugs related to parts colliding with Terrain water when they should not. The fix may impact some games.

The first is a bug where water does not react to Collision Groups. You can set the Terrain’s collision group, and if you have a part set to not collide with the Terrain’s group, it will still collide with water. We are fixing this so a group set to not collide with the Terrain’s group will ignore both the ground and the water.

It’s possible that your game is relying on this broken behavior unintentionally, where something is set to not collide with Terrain and its still floating. If you are explicitly relying on this behavior in your game, please let us know!

The other bug occurs where a part set to canCollide=false can still collide with water if listening for a touch event. This means you may have a floating structure that has non colliding parts with touch events that are contributing to buoyancy when they shouldn’t. We are fixing this so all non-colliding parts will not collide with water or impact buoyancy. You can disable the touch events on non-colliding parts to see how it should actually float.

We had this change activated for a bit this week then disabled it due to a game reporting issues. We want to give developers more time to make sure they won’t be affected.
You can find a handy example of both of these fixes impacting a game in this post from @opplo Terrain Water Breakage: CollisionGroups & Buoyancy
(cc @Tomarty for reporting)

The change has now been activated (Sept 3)


honestly was hoping for a fix for moving parts in water that include unions or weld constraint. last i tried, you cant build a prop with either of these or it will not move the boat. with surface welds being removed (the only thing you can use to make a usable propeller) this is a bit of a problem for people who prefer to use physics rather then body movers and such.


Glad to see irregularities being ironed out. It’s nice this update was delayed to help devs update to the new methods.

However; I really like the idea of having two collision groups for water and terrain, or being able to set the collision group of water separately from terrain.


Being able to define multiple collision groups for Terrain would be nice.


I agree! We want to do this in the future, but for now we do want to fix the irregularity like you said.


It would be nice to ignore water only while still allowing for terrain collision :smile: please

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Please forgive me if I’m simply stating the obvious -
I didn’t discover it myself, i’m sure I read it somewhere here on devforum from someone more clever than me - I found that if you use the region to create or clear away sections of water in your terrain - the strange connections/bondings of water to land aren’t as prevalent.
I also have a lot of luck using FillBlock and FillCylinder to call upon water into specific spaces creates the same tidy effect. Hope that helps.


Considering that there are obviously games that rely on this broken behavior, it is obvious that the terrain should be a creatable instance so that we can assign collision groups to different portions of our terrain.


The change is now activated. Please report any issues here!


By any chance were you able to allow us to ignore water but still collide with other terrain materials? :eyes:

See my previous reply …


4 posts were split to a new topic: Issue with unions not having collisions

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