Fix strange placement behavior for non-default Stairs+ nodes (#168)

Co-authored-by: Hugo Locurcio <hugo.locurcio@hugo.pro>

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- [Fixed strange placement behavior for non-default Stairs+ nodes.](https://github.com/minetest-mods/moreblocks/pull/168)
 - [Fixed stairs placement over oddly-shaped nodes.](https://github.com/minetest-mods/moreblocks/pull/166)
 
 ## [2.1.0] - 2020-12-14

stairsplus/common.lua

@@ -30,16 +30,25 @@ local wall_right_dirmap = {9, 18, 7, 12}
 local wall_left_dirmap = {11, 16, 5, 14}
 local ceil_dirmap = {20, 23, 22, 21}
 
+-- extract the stairsplus category from a node name
+-- assumes the name is in the form mod_name:category_original_ndoe_name
+local function name_to_category(name)
+	local colon = name:find(":") or 0
+	colon = colon + 1
+	local under = name:find("_", colon)
+	return name:sub(colon, under)
+end
+
 stairsplus.rotate_node_aux = function(itemstack, placer, pointed_thing)
 	local sneak = placer and placer:get_player_control().sneak
 	local aux = placer and placer:get_player_control().aux1
 
-	-- namestring for what we are placing, up to the first _ (exclusive)
-	local item_prefix = itemstack:get_name():gsub("_.*$", "")
-	-- namestring for what we are placing against
+	-- category for what we are placing
+	local item_prefix = name_to_category(itemstack:get_name())
+	-- category for what we are placing against
 	local under = pointed_thing.under
 	local under_node = minetest.get_node(under)
-	local under_prefix = under_node and under_node.name:gsub("_.*$", "")
+	local under_prefix = under_node and name_to_category(under_node.name)
 
 	local same_cat = item_prefix == under_prefix