First of all, is it fine to ask the same question here after asking on Discord or is this annoying (already asked there but got no answer)?
I am working on a project that features notes, similar like post-its, as the game world. Here you can see a quick sketch of a couple of notes that form a pond. The pond itself is made in shader graph, so we can dynamically increase or decrease the water level (needed for some levels). Now I want to render a particle system of small bubbles inside the pond.
All notes use the same material with a texture array, but all meshes are their own mesh. Do you have any ideas how I could mask my particles? It’s easy to mask them by the water line, but I don’t know how to mask them for the water area. If I use a render feature for the meshes only the bubbles will also be visible outside of the pond (i.e. in the ground).
So the question at the end is (I think…): Can I write the blue area in the stencil buffer via shader graph and then use it in a render feature to mask my particles? And if so, how do I do that? 
(If it is important how the body of water is rendered: The shader graph uses the world position with slight noise added to Y, smoothstep and masking by the texture array to be rendered. This works for each note individually, but I need all texture masks in one big texture to mask my particles. Since the notes are 3D meshes (and change position) a flat 2D texture won’t do it).
