Hi!
My project is 2D. I need to render some elements in a subviewport because I apply some shaders to them. It works all very well, except now these elements do not collide anymore with anything outside the subviewport. Am I doing something wrong or is it a limitation of subviewports?
Can 2D nodes in a subviewport collide with nodes outside?
xyz Well, if they are not parented to the subviewport they collide as they should. When parented under the subviewport they don't. I don't get any error, and that's why I am wondering if by design things parented to a subviewport cannot interact with things outside or if there some setting to manage that.
No signals involved. They are rigidbodies2D. When not parented under a subviewport they bounce on other colliders. When they are parented, they fall and go through. Gravity scale still works. And collision layers and masks work with other objects under the same viewport. But not with anything outside of it.
- Edited
ferruccio Make sure that the subviewport references the same World2D as the main viewport, so that they share the physics state Do print(get_viewport().world_2d) from a script attached to a node outside of subviewport as well as from the node that's inside subviewport. If they don't print the same object, it means that you have two different worlds, each running its own physics. If that's indeed the case, try assigning the main world to subviewport's world_2d property.
xyz Mmm... I did that and now the nodes in the subviewport now do interact with the ones outside. However, everything renders with the shaders in the subviewport, which was the thing I was trying to avoid.
In other words: if I assign the same world2d, it seems like the same rendering is applied to both sets of nodes. Ideally, I would like to apply the same world but have separate rendering but I just can't find a way to do so.
I solved it!
The solution was to do what you said (i.e. assign the world_2D of the level to the subviewport with the nodes with special shaders) but also to assign a specific visibility layer to the subviewport and then exclude that layer from the visibility cull mask of the level. So the subviewport is part of the same world, but the shaders are only visible in that viewport, which is exactly what I wanted.
Thanks a lot for the help @xyz 
I would have never solved this without the tip to look into world_2D!
read this in the docs this AM and thought of this post.... glad to see you found your answer.
"Note: Only collisions between objects within the same canvas (Viewport canvas or CanvasLayer) are supported. The behavior of collisions between objects in different canvases is undefined."
cool way for using viewports.