Fix stairs placement over oddly-shaped nodes (#166)

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- [Fixed stairs placement over oddly-shaped nodes.](https://github.com/minetest-mods/moreblocks/pull/166)
+
 ## [2.1.0] - 2020-12-14
 
 ### Added

stairsplus/common.lua

@@ -51,7 +51,10 @@ stairsplus.rotate_node_aux = function(itemstack, placer, pointed_thing)
 	-- and in general for sneak placement
 	local face_pos = minetest.pointed_thing_to_face_pos(placer, pointed_thing)
 	local face_off = vector.subtract(face_pos, under)
-	local wallmounted = minetest.dir_to_wallmounted(face_off)
+
+	-- we cannot trust face_off to tell us the correct directionif the
+	-- under node has a non-standard shape, so use the distance between under and above
+	local wallmounted = minetest.dir_to_wallmounted(vector.subtract(pointed_thing.above, under))
 
 	if same_cat and not aux then
 		p2 = under_node.param2