From 25ea72270dec5b0287b2a094d696bc807206b483 Mon Sep 17 00:00:00 2001
From: Christopher Head <chead@chead.ca>
Date: Wed, 16 Nov 2016 21:30:53 -0800
Subject: [PATCH] Use VoxelManipulators to force-load nodes.

If a node needed during wire traversal is not currently loaded, it is
loaded from disk using a VoxelManipulator.
---
 internal.lua |  8 +++--
 util.lua     | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 94 insertions(+), 3 deletions(-)

diff --git a/internal.lua b/internal.lua
index d012ee2..96f84e7 100644
--- a/internal.lua
+++ b/internal.lua
@@ -14,7 +14,7 @@ function digiline:importrules(spec, node)
 end
 
 function digiline:getAnyInputRules(pos)
-	local node = minetest.get_node(pos)
+	local node = digiline:get_node_force(pos)
 	local spec = digiline:getspec(node)
 	if not spec then return end
 
@@ -27,7 +27,7 @@ function digiline:getAnyInputRules(pos)
 end
 
 function digiline:getAnyOutputRules(pos)
-	local node = minetest.get_node(pos)
+	local node = digiline:get_node_force(pos)
 	local spec = digiline:getspec(node)
 	if not spec then return end
 
@@ -86,11 +86,12 @@ local function queue_dequeue(queue)
 end
 
 function digiline:transmit(pos, channel, msg, checked)
+	digiline:vm_begin()
 	local queue = queue_new()
 	queue_enqueue(queue, pos)
 	while not queue_empty(queue) do
 		local curPos = queue_dequeue(queue)
-		local node = minetest.get_node(curPos)
+		local node = digiline:get_node_force(curPos)
 		local spec = digiline:getspec(node)
 		if spec then
 			-- Effector actions --> Receive
@@ -114,4 +115,5 @@ function digiline:transmit(pos, channel, msg, checked)
 			end
 		end
 	end
+	digiline:vm_end()
 end
diff --git a/util.lua b/util.lua
index d138d63..cec75be 100644
--- a/util.lua
+++ b/util.lua
@@ -65,3 +65,92 @@ function digiline:tablecopy(table) -- deep table copy
 
 	return newtable
 end
+
+
+
+-- VoxelManipulator-based node access functions:
+
+-- Maps from a hashed mapblock position (as returned by hash_blockpos) to a
+-- table.
+--
+-- Contents of the table are:
+-- “va” → the VoxelArea
+-- “data” → the data array
+-- “param1” → the param1 array
+-- “param2” → the param2 array
+--
+-- Nil if no bulk-VM operation is in progress.
+local vm_cache = nil
+
+-- Starts a bulk-VoxelManipulator operation.
+--
+-- During a bulk-VoxelManipulator operation, calls to get_node_force operate
+-- directly on VM-loaded arrays, which should be faster for reading many nodes
+-- in rapid succession. However, the cache must be flushed with vm_end once the
+-- scan is finished, to avoid using stale data in future.
+function digiline:vm_begin()
+	vm_cache = {}
+end
+
+-- Ends a bulk-VoxelManipulator operation, freeing the cached data.
+function digiline:vm_end()
+	vm_cache = nil
+end
+
+-- The dimension of a mapblock in nodes.
+local MAPBLOCKSIZE = 16
+
+-- Converts a node position into a hash of a mapblock position.
+local function vm_hash_blockpos(pos)
+	return minetest.hash_node_position({
+		x = math.floor(pos.x / MAPBLOCKSIZE),
+		y = math.floor(pos.y / MAPBLOCKSIZE),
+		z = math.floor(pos.z / MAPBLOCKSIZE)
+	})
+end
+
+-- Gets the cache entry covering a position, populating it if necessary.
+local function vm_get_or_create_entry(pos)
+	local hash = vm_hash_blockpos(pos)
+	local tbl = vm_cache[hash]
+	if not tbl then
+		local vm = minetest.get_voxel_manip(pos, pos)
+		local min_pos, max_pos = vm:get_emerged_area()
+		local va = VoxelArea:new{MinEdge = min_pos, MaxEdge = max_pos}
+		tbl = {va = va, data = vm:get_data(), param1 = vm:get_light_data(), param2 = vm:get_param2_data()}
+		vm_cache[hash] = tbl
+	end
+	return tbl
+end
+
+-- Gets the node at a position during a bulk-VoxelManipulator operation.
+local function vm_get_node(pos)
+	local tbl = vm_get_or_create_entry(pos)
+	local index = tbl.va:indexp(pos)
+	local node_value = tbl.data[index]
+	local node_param1 = tbl.param1[index]
+	local node_param2 = tbl.param2[index]
+	return {name = minetest.get_name_from_content_id(node_value), param1 = node_param1, param2 = node_param2}
+end
+
+-- Gets the node at a given position, regardless of whether it is loaded or
+-- not.
+--
+-- Outside a bulk-VoxelManipulator operation, if the mapblock is not loaded, it
+-- is pulled into the server’s main map data cache and then accessed from
+-- there.
+--
+-- Inside a bulk-VoxelManipulator operation, the operation’s VM cache is used.
+function digiline:get_node_force(pos)
+	if vm_cache then
+		return vm_get_node(pos)
+	end
+	local node = minetest.get_node(pos)
+	if node.name == "ignore" then
+		-- Node is not currently loaded; use a VoxelManipulator to prime
+		-- the mapblock cache and try again.
+		minetest.get_voxel_manip(pos, pos)
+		node = minetest.get_node(pos)
+	end
+	return node
+end