Default: Prevent placing sapling if grown tree intersects protection

Add a global 'intersects protection' function to functions.lua for
checking if a specified volume intersects with a protected volume.
A 3D lattice of points are checked with an adjustable interval.
Add a global 'sapling on place' function to avoid duplicated code in
nodes.lua.

mods/default/functions.lua

@@ -481,3 +481,43 @@ minetest.register_abm({
 		end
 	end
 })
+
+
+--
+-- Checks if specified volume intersects a protected volume
+--
+
+function default.intersects_protection(minp, maxp, player_name, interval)
+	-- 'interval' is the largest allowed interval for the 3D lattice of checks
+
+	-- Compute the optimal float step 'd' for each axis so that all corners and
+	-- borders are checked. 'd' will be smaller or equal to 'interval'.
+	-- Subtracting 1e-4 ensures that the max co-ordinate will be reached by the
+	-- for loop (which might otherwise not be the case due to rounding errors).
+	local d = {}
+	for _, c in pairs({"x", "y", "z"}) do
+		if maxp[c] > minp[c] then
+			d[c] = (maxp[c] - minp[c]) / math.ceil((maxp[c] - minp[c]) / interval) - 1e-4
+		elseif maxp[c] == minp[c] then
+			d[c] = 1 -- Any value larger than 0 to avoid division by zero
+		else -- maxp[c] < minp[c], print error and treat as protection intersected
+			minetest.log("error", "maxp < minp in 'default.intersects_protection()'")
+			return true
+		end
+	end
+
+	for zf = minp.z, maxp.z, d.z do
+		local z = math.floor(zf + 0.5)
+		for yf = minp.y, maxp.y, d.y do
+			local y = math.floor(yf + 0.5)
+			for xf = minp.x, maxp.x, d.x do
+				local x = math.floor(xf + 0.5)
+				if minetest.is_protected({x = x, y = y, z = z}, player_name) then
+					return true
+				end
+			end
+		end
+	end
+
+	return false
+end

mods/default/nodes.lua

@@ -500,16 +500,30 @@ minetest.register_node("default:sapling", {
 	sunlight_propagates = true,
 	walkable = false,
 	on_timer = default.grow_sapling,
-	on_construct = function(pos)
-		minetest.get_node_timer(pos):start(math.random(2400,4800))
-	end,
 	selection_box = {
 		type = "fixed",
 		fixed = {-0.3, -0.5, -0.3, 0.3, 0.35, 0.3}
 	},
 	groups = {snappy = 2, dig_immediate = 3, flammable = 2,
 		attached_node = 1, sapling = 1},
 	sounds = default.node_sound_leaves_defaults(),
+
+	on_construct = function(pos)
+		minetest.get_node_timer(pos):start(math.random(2400,4800))
+	end,
+
+	on_place = function(itemstack, placer, pointed_thing)
+		itemstack = default.sapling_on_place(itemstack, placer, pointed_thing,
+			"default:sapling",
+			-- minp, maxp to be checked, relative to sapling pos
+			-- minp_relative.y = 1 because sapling pos has been checked
+			{x = -2, y = 1, z = -2},
+			{x = 2, y = 6, z = 2},
+			-- maximum interval of interior volume check
+			4)
+
+		return itemstack
+	end,
 })
 
 minetest.register_node("default:leaves", {
@@ -624,16 +638,30 @@ minetest.register_node("default:junglesapling", {
 	sunlight_propagates = true,
 	walkable = false,
 	on_timer = default.grow_sapling,
-	on_construct = function(pos)
-		minetest.get_node_timer(pos):start(math.random(2400,4800))
-	end,
 	selection_box = {
 		type = "fixed",
 		fixed = {-0.3, -0.5, -0.3, 0.3, 0.35, 0.3}
 	},
 	groups = {snappy = 2, dig_immediate = 3, flammable = 2,
 		attached_node = 1, sapling = 1},
 	sounds = default.node_sound_leaves_defaults(),
+
+	on_construct = function(pos)
+		minetest.get_node_timer(pos):start(math.random(2400,4800))
+	end,
+
+	on_place = function(itemstack, placer, pointed_thing)
+		itemstack = default.sapling_on_place(itemstack, placer, pointed_thing,
+			"default:junglesapling",
+			-- minp, maxp to be checked, relative to sapling pos
+			-- minp_relative.y = 1 because sapling pos has been checked
+			{x = -2, y = 1, z = -2},
+			{x = 2, y = 15, z = 2},
+			-- maximum interval of interior volume check
+			4)
+
+		return itemstack
+	end,
 })
 
 
@@ -691,16 +719,30 @@ minetest.register_node("default:pine_sapling", {
 	sunlight_propagates = true,
 	walkable = false,
 	on_timer = default.grow_sapling,
-	on_construct = function(pos)
-		minetest.get_node_timer(pos):start(math.random(2400,4800))
-	end,
 	selection_box = {
 		type = "fixed",
 		fixed = {-0.3, -0.5, -0.3, 0.3, 0.35, 0.3}
 	},
 	groups = {snappy = 2, dig_immediate = 3, flammable = 2,
 		attached_node = 1, sapling = 1},
 	sounds = default.node_sound_leaves_defaults(),
+
+	on_construct = function(pos)
+		minetest.get_node_timer(pos):start(math.random(2400,4800))
+	end,
+
+	on_place = function(itemstack, placer, pointed_thing)
+		itemstack = default.sapling_on_place(itemstack, placer, pointed_thing,
+			"default:pine_sapling",
+			-- minp, maxp to be checked, relative to sapling pos
+			-- minp_relative.y = 1 because sapling pos has been checked
+			{x = -2, y = 1, z = -2},
+			{x = 2, y = 12, z = 2},
+			-- maximum interval of interior volume check
+			4)
+
+		return itemstack
+	end,
 })
 
 
@@ -758,16 +800,30 @@ minetest.register_node("default:acacia_sapling", {
 	sunlight_propagates = true,
 	walkable = false,
 	on_timer = default.grow_sapling,
-	on_construct = function(pos)
-		minetest.get_node_timer(pos):start(math.random(2400,4800))
-	end,
 	selection_box = {
 		type = "fixed",
 		fixed = {-0.3, -0.5, -0.3, 0.3, 0.35, 0.3}
 	},
 	groups = {snappy = 2, dig_immediate = 3, flammable = 2,
 		attached_node = 1, sapling = 1},
 	sounds = default.node_sound_leaves_defaults(),
+
+	on_construct = function(pos)
+		minetest.get_node_timer(pos):start(math.random(2400,4800))
+	end,
+
+	on_place = function(itemstack, placer, pointed_thing)
+		itemstack = default.sapling_on_place(itemstack, placer, pointed_thing,
+			"default:acacia_sapling",
+			-- minp, maxp to be checked, relative to sapling pos
+			-- minp_relative.y = 1 because sapling pos has been checked
+			{x = -4, y = 1, z = -4},
+			{x = 4, y = 6, z = 4},
+			-- maximum interval of interior volume check
+			4)
+
+		return itemstack
+	end,
 })
 
 minetest.register_node("default:aspen_tree", {
@@ -824,17 +880,32 @@ minetest.register_node("default:aspen_sapling", {
 	sunlight_propagates = true,
 	walkable = false,
 	on_timer = default.grow_sapling,
-	on_construct = function(pos)
-		minetest.get_node_timer(pos):start(math.random(2400,4800))
-	end,
 	selection_box = {
 		type = "fixed",
 		fixed = {-0.3, -0.5, -0.3, 0.3, 0.35, 0.3}
 	},
 	groups = {snappy = 2, dig_immediate = 3, flammable = 2,
 		attached_node = 1, sapling = 1},
 	sounds = default.node_sound_leaves_defaults(),
+
+	on_construct = function(pos)
+		minetest.get_node_timer(pos):start(math.random(2400,4800))
+	end,
+
+	on_place = function(itemstack, placer, pointed_thing)
+		itemstack = default.sapling_on_place(itemstack, placer, pointed_thing,
+			"default:aspen_sapling",
+			-- minp, maxp to be checked, relative to sapling pos
+			-- minp_relative.y = 1 because sapling pos has been checked
+			{x = -2, y = 1, z = -2},
+			{x = 2, y = 12, z = 2},
+			-- maximum interval of interior volume check
+			4)
+
+		return itemstack
+	end,
 })
+
 --
 -- Ores
 --

mods/default/trees.lua

@@ -418,6 +418,7 @@ function default.grow_new_acacia_tree(pos)
 		path, "random", nil, false)
 end
 
+
 -- New aspen tree
 
 function default.grow_new_aspen_tree(pos)
@@ -426,3 +427,48 @@ function default.grow_new_aspen_tree(pos)
 	minetest.place_schematic({x = pos.x - 2, y = pos.y - 1, z = pos.z - 2},
 		path, "0", nil, false)
 end
+
+
+--
+-- Sapling 'on place' function to check protection of node and resulting tree volume
+--
+
+function default.sapling_on_place(itemstack, placer, pointed_thing,
+		sapling_name, minp_relative, maxp_relative, interval)
+	-- Position of sapling
+	local pos = pointed_thing.under
+	local node = minetest.get_node(pos)
+	local pdef = minetest.registered_nodes[node.name]
+	if not pdef or not pdef.buildable_to then
+		pos = pointed_thing.above
+		node = minetest.get_node(pos)
+		pdef = minetest.registered_nodes[node.name]
+		if not pdef or not pdef.buildable_to then
+			return itemstack
+		end
+	end
+
+	local player_name = placer:get_player_name()
+	-- Check sapling position for protection
+	if minetest.is_protected(pos, player_name) then
+		minetest.record_protection_violation(pos, player_name)
+		return itemstack
+	end
+	-- Check tree volume for protection
+	if not default.intersects_protection(
+			vector.add(pos, minp_relative),
+			vector.add(pos, maxp_relative),
+			player_name,
+			interval) then
+		minetest.set_node(pos, {name = sapling_name})
+		if not minetest.setting_getbool("creative_mode") then
+			itemstack:take_item()
+		end
+	else
+		minetest.record_protection_violation(pos, player_name)
+		-- Print extra information to explain
+		minetest.chat_send_player(player_name, "Tree will intersect protection")
+	end
+
+	return itemstack
+end