Fix and optimize line of sight checks

- Check destination medium against source, since it's possible
  to transition from a fluid to air and raycast will NOT collide
  with the air, causing from-fluid-to-air transitions not to be
  detected.
- Pre-cache fluid medium data for all node defs instead of running
  through logic at runtime.

szutil_cinecam/init.lua

@@ -94,42 +94,8 @@ local function setcamera(player, pos, target)
 	return player:set_pos(pos)
 end
 
-local function fluidmedium(pos)
-	local node = minetest.get_node(pos)
-	local def = minetest.registered_items[node.name]
-	if not def then return node.name end
-	if def.sunlight_propagates then return "CLEAR" end
-	return def.liquid_alternative_source or node.name
-end
-local function sightblocked(from, to)
-	local fsrc = fluidmedium(from)
-	for pt in minetest.raycast(from, to, false, true) do
-		if pt.type == "node" then
-			if fluidmedium(pt.under) ~= fsrc then
-				return pt.above
-			end
-		end
-	end
-end
-
-local getdata
-do
-	local datastore = {}
-	function getdata(p)
-		local pname = type(p) == "string" and p or p:get_player_name()
-		local data = datastore[pname]
-		if not data then
-			data = {}
-			datastore[pname] = data
-		end
-		return data
-	end
-	minetest.register_on_leaveplayer(function(player)
-			datastore[player:get_player_name()] = nil
-		end)
-end
-
 local allow
+local fluidmedium
 do
 	local allow_drawtypes = {
 		airlike = true,
@@ -149,17 +115,55 @@ do
 	local allow_nodes = {
 		ignore = true
 	}
+	local fluids = {}
 	minetest.after(0, function()
 			for k, v in pairs(minetest.registered_nodes) do
 				if allow_drawtypes[v.drawtype]
 				and v.paramtype == "light" then
 					allow_nodes[k] = true
 				end
+				if v.sunlight_propagates then
+					fluids[k] = "CLEAR"
+				else
+					fluids[k] = v.liquid_alternative_source or k
+				end
 			end
 		end)
 	allow = function(pos)
 		return allow_nodes[minetest.get_node(pos).name]
 	end
+	fluidmedium = function(pos)
+		return fluids[minetest.get_node(pos).name]
+	end
+end
+
+local function sightblocked(from, to)
+	local fsrc = fluidmedium(from)
+	for pt in minetest.raycast(from, to, false, true) do
+		if pt.type == "node" then
+			if fluidmedium(pt.under) ~= fsrc then
+				return pt.above
+			end
+		end
+	end
+	if fluidmedium(to) ~= fsrc then return to end
+end
+
+local getdata
+do
+	local datastore = {}
+	function getdata(p)
+		local pname = type(p) == "string" and p or p:get_player_name()
+		local data = datastore[pname]
+		if not data then
+			data = {}
+			datastore[pname] = data
+		end
+		return data
+	end
+	minetest.register_on_leaveplayer(function(player)
+			datastore[player:get_player_name()] = nil
+		end)
 end
 
 local function hudset(player, data, key, def)