1 files changed, 126 insertions, 0 deletions
diff --git a/builtin/game/forceloading.lua b/builtin/game/forceloading.lua
new file mode 100644
index 000000000..8043e5dea
--- /dev/null
+++ b/builtin/game/forceloading.lua
@@ -0,0 +1,126 @@
+-- Prevent anyone else accessing those functions
+local forceload_block = core.forceload_block
+local forceload_free_block = core.forceload_free_block
+core.forceload_block = nil
+core.forceload_free_block = nil
+
+local blocks_forceloaded
+local blocks_temploaded = {}
+local total_forceloaded = 0
+
+-- true, if the forceloaded blocks got changed (flag for persistence on-disk)
+local forceload_blocks_changed = false
+
+local BLOCKSIZE = core.MAP_BLOCKSIZE
+local function get_blockpos(pos)
+	return {
+		x = math.floor(pos.x/BLOCKSIZE),
+		y = math.floor(pos.y/BLOCKSIZE),
+		z = math.floor(pos.z/BLOCKSIZE)}
+end
+
+-- When we create/free a forceload, it's either transient or persistent. We want
+-- to add to/remove from the table that corresponds to the type of forceload, but
+-- we also need the other table because whether we forceload a block depends on
+-- both tables.
+-- This function returns the "primary" table we are adding to/removing from, and
+-- the other table.
+local function get_relevant_tables(transient)
+	if transient then
+		return blocks_temploaded, blocks_forceloaded
+	else
+		return blocks_forceloaded, blocks_temploaded
+	end
+end
+
+function core.forceload_block(pos, transient)
+	-- set changed flag
+	forceload_blocks_changed = true
+
+	local blockpos = get_blockpos(pos)
+	local hash = core.hash_node_position(blockpos)
+	local relevant_table, other_table = get_relevant_tables(transient)
+	if relevant_table[hash] ~= nil then
+		relevant_table[hash] = relevant_table[hash] + 1
+		return true
+	elseif other_table[hash] ~= nil then
+		relevant_table[hash] = 1
+	else
+		if total_forceloaded >= (tonumber(core.settings:get("max_forceloaded_blocks")) or 16) then
+			return false
+		end
+		total_forceloaded = total_forceloaded+1
+		relevant_table[hash] = 1
+		forceload_block(blockpos)
+		return true
+	end
+end
+
+function core.forceload_free_block(pos, transient)
+	-- set changed flag
+	forceload_blocks_changed = true
+
+	local blockpos = get_blockpos(pos)
+	local hash = core.hash_node_position(blockpos)
+	local relevant_table, other_table = get_relevant_tables(transient)
+	if relevant_table[hash] == nil then return end
+	if relevant_table[hash] > 1 then
+		relevant_table[hash] = relevant_table[hash] - 1
+	elseif other_table[hash] ~= nil then
+		relevant_table[hash] = nil
+	else
+		total_forceloaded = total_forceloaded-1
+		relevant_table[hash] = nil
+		forceload_free_block(blockpos)
+	end
+end
+
+-- Keep the forceloaded areas after restart
+local wpath = core.get_worldpath()
+local function read_file(filename)
+	local f = io.open(filename, "r")
+	if f==nil then return {} end
+	local t = f:read("*all")
+	f:close()
+	if t=="" or t==nil then return {} end
+	return core.deserialize(t) or {}
+end
+
+blocks_forceloaded = read_file(wpath.."/force_loaded.txt")
+for _, __ in pairs(blocks_forceloaded) do
+	total_forceloaded = total_forceloaded + 1
+end
+
+core.after(5, function()
+	for hash, _ in pairs(blocks_forceloaded) do
+		local blockpos = core.get_position_from_hash(hash)
+		forceload_block(blockpos)
+	end
+end)
+
+-- persists the currently forceloaded blocks to disk
+local function persist_forceloaded_blocks()
+	local data = core.serialize(blocks_forceloaded)
+	core.safe_file_write(wpath.."/force_loaded.txt", data)
+end
+
+-- periodical forceload persistence
+local function periodically_persist_forceloaded_blocks()
+
+	-- only persist if the blocks actually changed
+	if forceload_blocks_changed then
+		persist_forceloaded_blocks()
+
+		-- reset changed flag
+		forceload_blocks_changed = false
+	end
+
+	-- recheck after some time
+	core.after(10, periodically_persist_forceloaded_blocks)
+end
+
+-- persist periodically
+core.after(5, periodically_persist_forceloaded_blocks)
+
+-- persist on shutdown
+core.register_on_shutdown(persist_forceloaded_blocks)