Would be useful to be able to set a shader constant to a particular layer of a tilemap using tilemap.set_constant(): https://defold.com/ref/stable/tilemap/#tilemap.set_constant
Walking behind a wall or underneath a roof for example would set the tiles in an overhead layer to semi-transparent like so: tilemap.set_constant("#tilemap", "overhead", "tint", vmath.vector3(1, 1, 1, 0.5)).