add pseudoexponential decay to last-move smoke intensity (so it doesn't stay intense indefinitely after a large capture)

abm.lua

@@ -1,6 +1,6 @@
 -- LUALOCALS < ---------------------------------------------------------
-local include, nodecore
-= include, nodecore
+local include, nodecore, math
+= include, nodecore, math
 -- LUALOCALS > ---------------------------------------------------------
 
 minetest.register_abm({
@@ -10,6 +10,12 @@ minetest.register_abm({
                 nodenames = {"group:go_stone"},
                 action = function(pos, node)
                     if not (node.param2 == 0) then
+                        -- if smoke level is higher than 1, it can decay (lazy pseudoexponential decay)
+                        if math.random() < (0.01 * (node.param2 - 1)) then
+                            node.param2 = node.param2 - 1
+                            minetest.swap_node(pos, node)
+                        end
+
                         nodecore.smokefx(pos, 60, node.param2)
                     end
                 end