More precise logic for player names.

Try to detect player traces going through a change in fluid medium
such as water/air or water/glass, and block facial recognition
through it.

Specifically allow air-into-glass transitions, or into any other
medium otherwise clear enough to allow sunlight to propagate.

mods/nc_player_names/init.lua

@@ -10,9 +10,6 @@ local modname = minetest.get_current_modname()
 -- Maximum distance at which custom nametags are visible.
 local distance = tonumber(minetest.settings:get(modname .. "_distance")) or 16
 
--- Precision (number of steps) for line-of-sight check for displaying nametags
-local precision = tonumber(minetest.settings:get(modname .. "_precision")) or 50
-
 -- Keep track of active player HUDs.
 local huds = {}
 
@@ -70,14 +67,33 @@ local function canseeface(p1, n1, p2, n2)
 	local ld = (ll / 15 * distance)
 	if dsqr > (ld * ld) then return end
 
-	-- Check for line of sight from approximate eye level
-	-- of one player to the other.
+	-- Make sure players' eyes are inside the same fluid.
 	o1.y = o1.y + e1
 	o2.y = o2.y + e2
-	for pt in minetest.raycast(o1, o2) do
-		if pt.type ~= "object"
-		or (pt.ref ~= p2 and pt.ref ~= p1)
-		then return end
+	local f1 = minetest.get_node(o1).name
+	local d1 = minetest.registered_items[f1]
+	f1 = d1 and d1.liquid_alterantive_source or f1
+	local f2 = minetest.get_node(o2).name
+	local d2 = minetest.registered_items[f2]
+	f2 = d2 and d2.liquid_alterantive_source or f2
+	if f1 ~= f2 then return minetest.log(dump({f1, f2}))end
+
+	-- Check for line of sight from approximate eye level
+	-- of one player to the other.
+	for pt in minetest.raycast(o1, o2, true, true) do
+		if pt.type == "node" then
+			local nn = minetest.get_node(pt.under).name
+			local nd = minetest.registered_items[nn]
+			if not nd then return end
+			if not (f1 == "air" and nd.sunlight_propagates) then
+				nn = nd.liquid_alternative_source or nn
+				if nn ~= f1 then return end
+			end
+		elseif pt.type == "object" then
+			if pt.ref ~= p1 and pt.ref ~= p2 then return end
+		else
+			return
+		end
 	end
 
 	-- Players must be facing each other; cannot identify another