add snapping to grid

init.lua

@@ -26,6 +26,7 @@ dofile(MP .. "/craft.lua")
 dofile(MP .. "/record.lua")
 dofile(MP .. "/playback.lua")
 dofile(MP .. "/registry.lua")
+dofile(MP .. "/snap.lua")
 
 if minetest.get_modpath("mtt") and mtt.enabled then
 	dofile(MP .. "/configure.spec.lua")

place_tool.lua

@@ -3,19 +3,6 @@ local FORMSPEC_NAME = "pick_and_place:place"
 local has_mapsync = minetest.get_modpath("mapsync")
 local has_blockexchange = minetest.get_modpath("blockexchange")
 
-local function get_pos(meta, player)
-    local size = minetest.string_to_pos(meta:get_string("size"))
-    local distance = vector.distance(vector.new(), size)
-    local radius = math.ceil(distance / 2)
-    local offset = vector.round(vector.divide(size, 2))
-
-    local pos1 = pick_and_place.get_pointed_position(player, radius + 2)
-    pos1 = vector.subtract(pos1, offset)
-    local pos2 = vector.add(pos1, vector.subtract(size, 1))
-
-    return pos1, pos2
-end
-
 -- notify supported mods of changes
 local function notify_change(pos1, pos2)
     if has_blockexchange then
@@ -39,7 +26,8 @@ minetest.register_tool("pick_and_place:place", {
         local controls = player:get_player_control()
 
         local meta = itemstack:get_meta()
-        local pos1, pos2 = get_pos(meta, player)
+        local size = minetest.string_to_pos(meta:get_string("size"))
+        local pos1, pos2 = pick_and_place.get_placement_pos(size, player)
 
         if controls.aux1 then
             -- removal
@@ -85,7 +73,8 @@ minetest.register_tool("pick_and_place:place", {
         local controls = player:get_player_control()
 
         local meta = itemstack:get_meta()
-        local pos1, pos2 = get_pos(meta, player)
+        local size = minetest.string_to_pos(meta:get_string("size"))
+        local pos1, pos2 = pick_and_place.get_placement_pos(size, player)
 
         if controls.aux1 then
             -- removal preview

snap.lua

@@ -0,0 +1,81 @@
+
+-- playername -> pos
+local origin_map = {}
+
+-- playername -> size
+local size_map = {}
+-- TODO: persistence per player (load on join, save on set)
+
+local function snap_axis(axis, origin, size, pos)
+    local half_size = math.ceil(size[axis] / 2)
+
+    -- delta from origin
+    local diff = pos[axis] - origin[axis]
+    local o = diff % size[axis]
+    if o >= half_size then
+        -- round up
+        pos[axis] = pos[axis] + (size[axis] - o)
+    elseif o > 0 then
+        -- round down
+        pos[axis] = pos[axis] - o
+    end
+end
+
+function pick_and_place.get_placement_pos(size, player)
+    local distance = vector.distance(vector.new(), size)
+    local radius = math.ceil(distance / 2)
+    local offset = vector.round(vector.divide(size, 2))
+    local playername = player:get_player_name()
+
+    local pos1 = pick_and_place.get_pointed_position(player, radius + 2)
+    pos1 = vector.subtract(pos1, offset)
+
+    local origin = origin_map[playername]
+    local snap_size = size_map[playername]
+    if origin and snap_size then
+        -- apply grid-snapping
+        snap_axis("x", origin, size, pos1)
+        snap_axis("y", origin, size, pos1)
+        snap_axis("z", origin, size, pos1)
+    end
+
+    local pos2 = vector.add(pos1, vector.subtract(size, 1))
+    return pos1, pos2
+end
+
+minetest.register_chatcommand("pnp_snap", {
+    params = "[on|off]",
+    description = "enable or disable grid snapping with the current placement tool dimensions and origin",
+    func = function(name, param)
+        if param == "on" then
+            -- enable grid
+            local player = minetest.get_player_by_name(name)
+            if not player then
+                return false, "player not found"
+            end
+            local itemstack = player:get_wielded_item()
+            if itemstack:get_name() ~= "pick_and_place:place" then
+                return false, "no placement tool selected"
+            end
+
+            local meta = itemstack:get_meta()
+            local size = minetest.string_to_pos(meta:get_string("size"))
+            local pos1 = pick_and_place.get_placement_pos(size, player)
+
+            origin_map[name] = pos1
+            size_map[name] = size
+
+        elseif param == "off" then
+            -- disable grid
+            origin_map[name] = nil
+            size_map[name] = nil
+        end
+
+        if origin_map[name] then
+            return true, "grid set with origin: " .. minetest.pos_to_string(origin_map[name]) ..
+                " and size: " .. minetest.pos_to_string(size_map[name])
+        else
+            return true, "grid disabled"
+        end
+    end
+})