Working with pen and paper to sketch different ways to implement a natural-looking transition from one tile type to another, like a shoreline. I also had time to do some testing with programmatically generating masks to clip tile textures. The basic idea is simple, but it can quickly become a bit messy if a water tile is bordered by one tile type to the north, and another to the south, and yet third to the west. Yes, we could draw the clipped-with-mask piece of another tile type on top of the water tile once per different neighbouring tile type. But I try to pass all the necessary data to the shader at one go, using red channel to mean "clip from texture A", and so on. Designing it so that the same approach should work both on 2D and 3D tilemap.