lmark.synchronized_markers(): apply one marker's effects to multiple points simultaneously.

synchronized_markers() takes a marker, and a list of method names to override,
and returns a set of markers that fire simultaneously, to allow, say, fog
machines that fire at random intervals, but always fire in unison. lm_mslav.lua
has details. volcano.des has an example volcano entry vault that uses this.

Allow fetching a list of Lua markers/marker positions by property value.

Renamed dgn.find_marker_prop -> dgn.find_marker_position_by_prop.

s/helper/listener/ for fog machine listeners.

16 files changed, 506 insertions, 127 deletions

diff --git a/crawl-ref/source/clua.cc b/crawl-ref/source/clua.cc
index d9273b74c9..64fd63b768 100644
--- a/crawl-ref/source/clua.cc
+++ b/crawl-ref/source/clua.cc
@@ -12,6 +12,7 @@
 #include "l_libs.h"
 
 #include "files.h"
+#include "libutil.h"
 #include "state.h"
 #include "stuff.h"
 
@@ -275,7 +276,7 @@ bool CLua::runhook(const char *hook, const char *params, ...)
 
     // Remember top of stack, for debugging porpoises
     int stack_top = lua_gettop(ls);
-    lua_getglobal(ls, hook);
+    pushglobal(hook);
     if (!lua_istable(ls, -1))
     {
         lua_pop(ls, 1);
@@ -475,7 +476,7 @@ bool CLua::callbooleanfn(bool def, const char *fn, const char *params, ...)
 
     int stacktop = lua_gettop(ls);
 
-    lua_getglobal(ls, fn);
+    pushglobal(fn);
     if (!lua_isfunction(ls, -1))
     {
         lua_pop(ls, 1);
@@ -497,6 +498,46 @@ bool CLua::proc_returns(const char *par) const
     return (strchr(par, '>') != NULL);
 }
 
+// Identical to lua_getglobal for simple names, but will look up
+// "a.b.c" names in tables, so you can pushglobal("dgn.point") and get
+// _G['dgn']['point'], as expected.
+//
+// Guarantees to push exactly one value onto the stack.
+//
+void CLua::pushglobal(const std::string &name)
+{
+    std::vector<std::string> pieces = split_string(".", name);
+    lua_State *ls(state());
+
+    if (pieces.empty())
+        lua_pushnil(ls);
+
+    for (unsigned i = 0, size = pieces.size(); i < size; ++i)
+    {
+        if (!i)
+            lua_getglobal(ls, pieces[i].c_str());
+        else
+        {
+            if (lua_istable(ls, -1))
+            {
+                lua_pushstring(ls, pieces[i].c_str());
+                lua_gettable(ls, -2);
+                // Swap the value we just found with the table itself.
+                lua_insert(ls, -2);
+                // And remove the table.
+                lua_pop(ls, 1);
+            }
+            else
+            {
+                // We expected a table here, but got something else. Fail.
+                lua_pop(ls, 1);
+                lua_pushnil(ls);
+                break;
+            }
+        }
+    }
+}
+
 bool CLua::callfn(const char *fn, const char *params, ...)
 {
     error.clear();
@@ -504,7 +545,7 @@ bool CLua::callfn(const char *fn, const char *params, ...)
     if (!ls)
         return (false);
 
-    lua_getglobal(ls, fn);
+    pushglobal(fn);
     if (!lua_isfunction(ls, -1))
     {
         lua_pop(ls, 1);
@@ -536,7 +577,7 @@ bool CLua::callfn(const char *fn, int nargs, int nret)
     // If a function is not provided on the stack, get the named function.
     if (fn)
     {
-        lua_getglobal(ls, fn);
+        pushglobal(fn);
         if (!lua_isfunction(ls, -1))
         {
             lua_settop(ls, -nargs - 2);
@@ -1139,4 +1180,3 @@ bool lua_datum::is_udata() const
 {
     LUA_CHECK_TYPE(lua_isuserdata);
 }
-
diff --git a/crawl-ref/source/clua.h b/crawl-ref/source/clua.h
index a72d56159b..1bbf70c720 100644
--- a/crawl-ref/source/clua.h
+++ b/crawl-ref/source/clua.h
@@ -126,6 +126,8 @@ public:
     int execfile(const char *filename, bool trusted = false,
                  bool die_on_fail = false);
 
+    void pushglobal(const std::string &name);
+
     bool callbooleanfn(bool defval, const char *fn, const char *params, ...);
     bool callfn(const char *fn, int nargs, int nret = 1);
     bool callfn(const char *fn, const char *params, ...);
diff --git a/crawl-ref/source/cluautil.cc b/crawl-ref/source/cluautil.cc
index e55b836f3e..a9cb1cec7b 100644
--- a/crawl-ref/source/cluautil.cc
+++ b/crawl-ref/source/cluautil.cc
@@ -99,25 +99,24 @@ void clua_register_metatable(lua_State *ls, const char *tn,
     }
 }
 
-
-template <typename list, typename lpush>
-static int dlua_gentable(lua_State *ls, const list &strings, lpush push)
+int clua_pushcxxstring(lua_State *ls, const std::string &s)
 {
-    lua_newtable(ls);
-    for (int i = 0, size = strings.size(); i < size; ++i)
-    {
-        push(ls, strings[i]);
-        lua_rawseti(ls, -2, i + 1);
-    }
+    lua_pushstring(ls, s.c_str());
     return (1);
 }
 
-inline static void dlua_pushcxxstring(lua_State *ls, const std::string &s)
+int clua_stringtable(lua_State *ls, const std::vector<std::string> &s)
 {
-    lua_pushstring(ls, s.c_str());
+    return clua_gentable(ls, s, clua_pushcxxstring);
 }
 
-int dlua_stringtable(lua_State *ls, const std::vector<std::string> &s)
+int clua_pushpoint(lua_State *ls, const coord_def &pos)
 {
-    return dlua_gentable(ls, s, dlua_pushcxxstring);
+    lua_pushnumber(ls, pos.x);
+    lua_pushnumber(ls, pos.y);
+    CLua &vm(CLua::get_vm(ls));
+    if (!vm.callfn("dgn.point", 2, 1))
+        luaL_error(ls, "dgn.point(%d,%d) failed: %s",
+                   pos.x, pos.y, vm.error.c_str());
+    return (1);
 }
diff --git a/crawl-ref/source/cluautil.h b/crawl-ref/source/cluautil.h
index 8ea98028ee..0f02555750 100644
--- a/crawl-ref/source/cluautil.h
+++ b/crawl-ref/source/cluautil.h
@@ -57,7 +57,7 @@ void clua_register_metatable(lua_State *ls, const char *tn,
                              const luaL_reg *lr,
                              int (*gcfn)(lua_State *ls) = NULL);
 
-int dlua_stringtable(lua_State *ls, const std::vector<std::string> &s);
+int clua_stringtable(lua_State *ls, const std::vector<std::string> &s);
 
 /*
  * User-data templates.
@@ -175,4 +175,20 @@ dgn_event *var = *(dgn_event **) luaL_checkudata(ls, n, DEVENT_METATABLE)
 #define MAPMARKER(ls, n, var) \
 map_marker *var = *(map_marker **) luaL_checkudata(ls, n, MAPMARK_METATABLE)
 
+
+template <typename list, typename lpush>
+static int clua_gentable(lua_State *ls, const list &strings, lpush push)
+{
+    lua_newtable(ls);
+    for (int i = 0, size = strings.size(); i < size; ++i)
+    {
+        push(ls, strings[i]);
+        lua_rawseti(ls, -2, i + 1);
+    }
+    return (1);
+}
+
+int clua_pushcxxstring(lua_State *ls, const std::string &s);
+int clua_pushpoint(lua_State *ls, const coord_def &pos);
+
 #endif
diff --git a/crawl-ref/source/dat/clua/lm_fog.lua b/crawl-ref/source/dat/clua/lm_fog.lua
index d893a150d2..97bc5750c4 100644
--- a/crawl-ref/source/dat/clua/lm_fog.lua
+++ b/crawl-ref/source/dat/clua/lm_fog.lua
@@ -48,11 +48,13 @@
 -- start_clouds: The number of clouds to lay when the level containing
 --     the cloud machine is entered.  This is necessary since clouds
 --     are cleared when the player leaves a level.
--- helper: A FunctionMachine helper marker. Will be called whenever the countdown
---     is activated, and whenever the fog machine is reset. It will be called
---     with the FogMachine's marker, a string containing the event ("decrement",
---     "trigger"), the actual event object, and a copy of the FogMachine itself.
---     See the section "Messages for fog machines" at the end of the file.
+-- listener: A FunctionMachine listener marker. Will be called
+--     whenever the countdown is activated, and whenever the fog
+--     machine is reset. It will be called with the FogMachine's
+--     marker, a string containing the event ("decrement", "trigger"),
+--     the actual event object, and a copy of the FogMachine itself.
+--     See the section "Messages for fog machines" at the end of the
+--     file.
 --
 ------------------------------------------------------------------------------
 
@@ -96,7 +98,7 @@ function FogMachine:new(pars)
   m.size_max     = pars.size_max     or pars.size
   m.spread_rate  = pars.spread_rate  or -1
   m.start_clouds = pars.start_clouds or 1
-  m.helper       = pars.helper       or nil
+  m.listener     = pars.listener     or nil
 
   m.size_buildup_amnt   = pars.size_buildup_amnt   or 0
   m.size_buildup_time   = pars.size_buildup_time   or 1
@@ -109,10 +111,16 @@ function FogMachine:new(pars)
   return m
 end
 
-function FogMachine:do_fog(marker)
-  local x, y = marker:pos()
+function FogMachine:apply_cloud(point, pow_min, pow_max, pow_rolls,
+                                size, cloud_type, kill_cat, spread)
+  dgn.apply_area_cloud(point.x, point.y, pow_min, pow_max, pow_rolls, size,
+                       cloud_type, kill_cat, spread)
+end
+
+function FogMachine:do_fog(point)
+  local p = point
   if self.walk_dist > 0 then
-    x, y = dgn.random_walk(x, y, self.walk_dist)
+    p = dgn.point(dgn.random_walk(p.x, p.y, self.walk_dist))
   end
 
   local buildup_turns = self.buildup_turns
@@ -142,9 +150,9 @@ function FogMachine:do_fog(marker)
   local spread = self.spread_rate + (self.spread_buildup_amnt * buildup_turns /
                                      self.spread_buildup_time)
 
-  dgn.apply_area_cloud(x, y, self.pow_min, self.pow_max, self.pow_rolls,
-                       crawl.random_range(size_min, size_max, 1),
-                       self.cloud_type, self.kill_cat, spread)
+  self:apply_cloud(p, self.pow_min, self.pow_max, self.pow_rolls,
+                   crawl.random_range(size_min, size_max, 1),
+                   self.cloud_type, self.kill_cat, spread)
 end
 
 function FogMachine:activate(marker, verbose)
@@ -153,6 +161,12 @@ function FogMachine:activate(marker, verbose)
   dgn.register_listener(dgn.dgn_event_type('entered_level'), marker)
 end
 
+function FogMachine:notify_listener(point, event, evobj)
+  if self.listener then
+    return self.listener:do_function(point, event, ev, self)
+  end
+end
+
 function FogMachine:event(marker, ev)
   local _x, _y = marker:pos()
   if ev:type() == dgn.dgn_event_type('turn') then
@@ -164,23 +178,21 @@ function FogMachine:event(marker, ev)
       self.buildup_turns = self.size_buildup_time
     end
 
-    if self.helper ~= nil and self.countdown > 0 then
-      self.helper:do_function(marker, "decrement", ev, self)
-    elseif self.helper ~= nil and self.countdown <= 0 then
-      self.helper:do_function(marker, "trigger", ev, self)
+    if self.countdown > 0 then
+      self:notify_listener(dgn.point(marker:pos()), "decrement", ev)
+    elseif self.countdown <= 0 then
+      self:notify_listener(dgn.point(marker:pos()), "trigger", ev)
     end
 
     while self.countdown <= 0 do
-     self:do_fog(marker)
-     self.countdown = self.countdown +
+      self:do_fog(dgn.point(marker:pos()))
+      self.countdown = self.countdown +
         crawl.random_range(self.delay_min, self.delay_max, 1)
     end
   elseif ev:type() == dgn.dgn_event_type('entered_level') then
     for i = 1, self.start_clouds do
-      self:do_fog(marker)
-      if self.helper ~= nil then
-        self.helper:do_function(marker, "trigger", ev, self)
-      end
+      self:do_fog(dgn.point(marker:pos()))
+      self:notify_listener(dgn.point(marker:pos()), "trigger", ev)
       self.countdown = crawl.random_range(self.delay_min, self.delay_max, 1)
       self.buildup_turns = 0
     end
@@ -206,9 +218,9 @@ function FogMachine:write(marker, th)
   file.marshall(th, self.spread_buildup_time)
   file.marshall(th, self.buildup_turns)
   file.marshall(th, self.countdown)
-  if self.helper ~= nil then
+  if self.listener then
     file.marshall_meta(th, true)
-    self.helper:write(marker, th)
+    self.listener:write(marker, th)
   else
     file.marshall_meta(th, false)
   end
@@ -233,12 +245,15 @@ function FogMachine:read(marker, th)
   self.spread_buildup_time = file.unmarshall_number(th)
   self.buildup_turns       = file.unmarshall_number(th)
   self.countdown           = file.unmarshall_number(th)
-  got_helper               = file.unmarshall_meta(th)
-  if got_helper == true then
-    self.helper = function_machine ({marker_type = "helper", func = (function() end)})
-    self.helper:read(marker, th)
+  got_listener               = file.unmarshall_meta(th)
+  if got_listener == true then
+    self.listener = function_machine {
+      marker_type = "listener",
+      func = (function() end)
+    }
+    self.listener:read(marker, th)
   else
-    self.helper = nil
+    self.listener = nil
   end
 
   setmetatable(self, FogMachine)
@@ -280,41 +295,46 @@ end
 -------------------------------------------------------------------------------
 -- Messages for fog machines.
 --
---  * warning_machine: Takes three parameters: turns, cantsee_message, and,
---      optionally, see_message. Turns is the value of player turns before to
---      trigger the message before the fog machine is fired. If only see_message
---      is provided, the message will only be printed if the player can see the
---      fog machine. If only cantsee_mesage is provided, the message will be
---      displayed regardless. In combination, the message will be different
---      depending on whether or not the player can see the marker. By default, the
---      message will be displaying using the "warning" channel.
+-- * warning_machine: Takes three parameters: turns, cantsee_message,
+--      and, optionally, see_message. Turns is the value of player
+--      turns before to trigger the message before the fog machine is
+--      fired. If only see_message is provided, the message will only
+--      be printed if the player can see the fog machine. If only
+--      cantsee_mesage is provided, the message will be displayed
+--      regardless. In combination, the message will be different
+--      depending on whether or not the player can see the marker. By
+--      default, the message will be displaying using the "warning"
+--      channel.
 --
---  * trigger_machine: Takes three parameters: cantsee_message, see_message, and,
---      optionally, channel. The functionality is identical to a warning_machine,
---      only the message is instead displayed (or not displayed) when the fog machine
---      is triggered. The message channel can be provided.
+-- * trigger_machine: Takes three parameters: cantsee_message,
+--      see_message, and, optionally, channel. The functionality is
+--      identical to a warning_machine, only the message is instead
+--      displayed (or not displayed) when the fog machine is
+--      triggered. The message channel can be provided.
 --
---  * tw_machine: Combines the above two message machines, providing warning messages
---      as well as messages when triggered. Takes the parameters: warn_turns,
---      warning_cantsee_message, trigger_cantsee_message, trigger_channel,
---      trigger_see_message, warning_see_message. Parameters work as described above.
+-- * tw_machine: Combines the above two message machines, providing
+--      warning messages as well as messages when triggered. Takes the
+--      parameters: warn_turns, warning_cantsee_message,
+--      trigger_cantsee_message, trigger_channel, trigger_see_message,
+--      warning_see_message. Parameters work as described above.
 --
--- In all instances, the "cantsee" form of the message parameter cannot be null,
--- and for warning and dual trigger/warning machines, the turns parameter cannot
--- be null. All other parameters are considered optional.
+-- In all instances, the "cantsee" form of the message parameter
+-- cannot be null, and for warning and dual trigger/warning machines,
+-- the turns parameter cannot be null. All other parameters are
+-- considered optional.
 
 function warning_machine (trns, cantsee_mesg, see_mesg)
   if trns == nil or (see_mesg == nil and cantsee_mesg == nil) then
     error("WarningMachine requires turns and message!")
   end
-  local function warning_func (marker, mtable, m2, event_name, event, fm)
+  local function warning_func (point, mtable, event_name, event, fm)
     local countdown = fm.countdown
     if event_name == "decrement" and countdown <= mtable.turns then
-      if mtable.warning_done ~= true then
-        if mtable.see_message ~= nil and you.see_cell(marker:pos()) then
-            crawl.mpr(mtable.see_message, "warning")
-        elseif mtable.cantsee_message ~= nil then
-            crawl.mpr(mtable.cantsee_message, "warning")
+      if not mtable.warning_done then
+        if mtable.see_message and you.see_cell(point.x, point.y) then
+          crawl.mpr(mtable.see_message, "warning")
+        elseif mtable.cantsee_message then
+          crawl.mpr(mtable.cantsee_message, "warning")
         end
         mtable.warning_done = true
       end
@@ -322,7 +342,7 @@ function warning_machine (trns, cantsee_mesg, see_mesg)
       mtable.warning_done = false
     end
   end
-  pars = {marker_type = "helper"}
+  pars = {marker_type = "listener"}
   pars.marker_params = {see_message = see_mesg, cantsee_message = cantsee_mesg,
                         turns = trns * 10, warning_done = false}
   pars.func = warning_func
@@ -333,34 +353,40 @@ function trigger_machine (cantsee_mesg, see_mesg, chan)
   if see_mesg == nil and cantsee_mesg == nil then
     error("Triggermachine requires a message!")
   end
-  local function trigger_func (marker, mtable, m2, event_name, event, fm)
+  local function trigger_func (point, mtable, event_name, event, fm)
     local countdown = fm.countdown
     if event_name == "trigger" then
       channel = mtable.channel or ""
-      if mtable.see_message ~= nil and you.see_cell(marker:pos()) then
+      if mtable.see_message ~= nil and you.see_cell(point.x, point.y) then
         crawl.mpr(mtable.see_message, channel)
       elseif mtable.cantsee_message ~= nil then
         crawl.mpr(mtable.cantsee_message, channel)
       end
     end
   end
-  pars = {marker_type = "helper"}
-  pars.marker_params = {channel = chan or nil, see_message = see_mesg, cantsee_message = cantsee_mesg}
+  pars = {marker_type = "listener"}
+  pars.marker_params = {
+    channel = chan or nil,
+    see_message = see_mesg,
+    cantsee_message = cantsee_mesg
+  }
   pars.func = trigger_func
   return FunctionMachine:new(pars)
 end
 
-function tw_machine (warn_turns, warn_cantsee_message, trig_cantsee_message, trig_channel,
+function tw_machine (warn_turns, warn_cantsee_message,
+                     trig_cantsee_message, trig_channel,
                      trig_see_message, warn_see_message)
-  if warn_turns == nil or (warn_see_message == nil and warn_cantsee_message == nil)
-                       or (trig_see_message == nil and trig_cantsee_message == nil) then
-    error("TWMachine needs warning turns, warning message and triggeing message.")
+  if (not warn_turns or (not warn_see_message and not warn_cantsee_message)
+      or (not trig_see_message and not trig_cantsee_message)) then
+    error("TWMachine needs warning turns, warning message and "
+          .. "triggering message.")
   end
-  local function tw_func (marker, mtable, m2, event_name, event, fm)
+  local function tw_func (point, mtable, event_name, event, fm)
     local countdown = fm.countdown
     if event_name == "decrement" and countdown <= mtable.warning_turns then
       if mtable.warning_done ~= true then
-        if mtable.warning_see_message ~= nil and you.see_cell(marker:pos()) then
+        if mtable.warning_see_message and you.see_cell(point.x, point.y) then
           crawl.mpr(mtable.warning_see_message, "warning")
         elseif mtable.warning_cantsee_message ~= nil then
           crawl.mpr(mtable.warning_cantsee_message, "warning")
@@ -370,17 +396,23 @@ function tw_machine (warn_turns, warn_cantsee_message, trig_cantsee_message, tri
     elseif event_name == "trigger" then
       mtable.warning_done = false
       channel = mtable.trigger_channel or ""
-      if mtable.trigger_see_message ~= nil and you.see_cell(marker:pos()) then
+      if mtable.trigger_see_message and you.see_cell(point.x, point.y) then
         crawl.mpr(mtable.trigger_see_message, channel)
       elseif mtable.trigger_cantsee_message ~= nil then
         crawl.mpr(mtable.trigger_cantsee_message, channel)
       end
     end
   end
-  pars = {marker_type = "helper"}
-  pars.marker_params = {warning_see_message = warn_see_message, warning_cantsee_message = warn_cantsee_message,
-                        warning_turns = warn_turns * 10, warning_done = false, trigger_see_message = trig_see_message,
-                        trigger_cantsee_message = trig_cantsee_message, trigger_channel = trig_channel or nil}
+  pars = {marker_type = "listener"}
+  pars.marker_params = {
+    warning_see_message = warn_see_message,
+    warning_cantsee_message = warn_cantsee_message,
+    warning_turns = warn_turns * 10,
+    warning_done = false,
+    trigger_see_message = trig_see_message,
+    trigger_cantsee_message = trig_cantsee_message,
+    trigger_channel = trig_channel or nil
+  }
   pars.func = tw_func
   return FunctionMachine:new(pars)
 end
diff --git a/crawl-ref/source/dat/clua/lm_func.lua b/crawl-ref/source/dat/clua/lm_func.lua
index b76d6cdc9a..cd83cf61a3 100644
--- a/crawl-ref/source/dat/clua/lm_func.lua
+++ b/crawl-ref/source/dat/clua/lm_func.lua
@@ -21,12 +21,14 @@
 --    * "player_at": Calls the function whenever the player is at the
 --       same position as the marker. Takes the same "repeated"
 --       parameter as "in_los".
---    * "helper": A function machine that can be linked into other lua markers
---       and machines. It is not triggered independantly, but called by the "parent"
---       marker, though always with the same marker_table parameter as other
---       machines. May take further parameters, see the parent's documentation.
+--    * "helper": A function machine that can be linked into other lua
+--       markers and machines. It is not triggered independantly, but
+--       called by the "parent" marker, though always with the same
+--       marker_table parameter as other machines. May take further
+--       parameters, see the parent's documentation.
 --
---  marker_table: Table to be passed to the function when called. Defaults to {}.
+--  marker_table: Table to be passed to the function when called.
+--  Defaults to {}.
 --
 -- Specific markers take specific parameters, as listed under marker_type.
 --
@@ -95,13 +97,12 @@ function FunctionMachine:new(pars)
   return m
 end
 
-function FunctionMachine:do_function(...)
-  marker = arg[1]
-  local _x, _y = marker:pos()
-  if #arg == 1 then
-    self.func(marker, self.marker_params)
+function FunctionMachine:do_function(position, ...)
+  local largs = { ... }
+  if #largs == 0 then
+    self.func(position, self.marker_params)
   else
-    self.func(marker, self.marker_params, unpack(arg))
+    self.func(position, self.marker_params, unpack(largs))
   end
 end
 
@@ -121,7 +122,7 @@ function FunctionMachine:event(marker, ev)
       self.countdown = self.countdown - ev:ticks()
 
       while self.countdown <= 0 do
-        self:do_function(marker)
+        self:do_function(dgn.point(marker:pos()))
         self.activated = true
         self.countdown = self.countdown +
           crawl.random_range(self.turns_min, self.turns_max, 1)
@@ -129,7 +130,7 @@ function FunctionMachine:event(marker, ev)
     elseif self.marker_type == "in_los" then
       if you.see_cell(x, y) then
         if not self.activated or self.repeated then
-          self:do_function(marker)
+          self:do_function(dgn.point(marker:pos()))
           self.activated = true
         end
       end
@@ -137,7 +138,7 @@ function FunctionMachine:event(marker, ev)
       you_x, you_y = you.pos()
       if you_x == x and you_y == y then
         if not self.activated or self.repeated then
-          self:do_function(marker)
+          self:do_function(dgn.point(marker:pos()))
           self.activated = true
         end
       end
@@ -178,7 +179,9 @@ end
 function message_machine (pars)
   local channel = pars.channel or false
   local mtable = {message = pars.message, channel = pars.channel}
-  pars.func = (function(marker, mtable) crawl.mpr(mtable.message, mtable.channel) end)
+  pars.func = function (position, mtable)
+                crawl.mpr(mtable.message, mtable.channel)
+              end
   pars.marker_params = mtable
   return FunctionMachine:new(pars)
 end
diff --git a/crawl-ref/source/dat/clua/lm_mslav.lua b/crawl-ref/source/dat/clua/lm_mslav.lua
new file mode 100644
index 0000000000..141dea7521
--- /dev/null
+++ b/crawl-ref/source/dat/clua/lm_mslav.lua
@@ -0,0 +1,157 @@
+----------------------------------------------------------------------------
+-- lm_mslav.lua
+--
+-- Wraps a marker to act as a master firing synchronized events to its
+-- own position, and to any number of (or zero) slave markers'
+-- positions.
+--
+-- API: lmark.synchronized_markers(<marker>, <trigger-function-names>)
+--
+-- Usage:
+-- ------
+--
+-- You can use synchronized_markers() if you have a marker that
+-- performs an activity at random intervals, and you want to apply
+-- this marker's effects to multiple locations at the same time.
+--
+-- As an example, take a fog machine:
+-- 1) Create the fog machine as you would normally:
+--        local fog = fog_machine {
+--                            cloud_type = 'flame',
+--                            size = 3, pow_min=2,
+--                            pow_max = 5, delay_min = 22, delay_max = 120,
+--                          }
+--
+-- 2) Apply it as a Lua marker to one or more locations, wrapping it
+--    with synchronized_markers():
+--        lua_marker('m', lmark.synchronized_markers(fog, 'do_fog'))
+--    Where 'do_fog' is the name of the trigger method on the
+--    underlying marker (here the fog machine) that performs the
+--    activity of interest (generating fog at some point). The first
+--    parameter of this overridden method must be a dgn.point that
+--    specifies where the effect occurs. The method may also take any
+--    number of additional parameters.
+--
+--    You may override multiple methods on the base marker:
+--        lmark.synchronized_markers(fog, 'do_fog', 'notify_listener')
+--    The only requirement for an overridden method is that it take a
+--    dgn.point as its first parameter.
+--
+-- Internals:
+-- ---------
+-- synchronized_markers() takes one marker instance, and creates one
+-- master marker (which is based on the given marker instance) and
+-- multiple slave markers (which are simple PortalDescriptor markers).
+-- The only purpose of the slave markers is to be discoverable by
+-- dgn.find_marker_positions_by_prop, given a unique, autogenerated
+-- slave id.
+--
+-- The master marker operates normally, but calls to any of the trigger
+-- methods (say 'do_fog') are intercepted. Every trigger call is performed
+-- on the master's position, and then on all the slaves' positions.
+----------------------------------------------------------------------------
+
+util.namespace('lmark')
+
+lmark.slave_cookie = 0
+
+function lmark.next_slave_id()
+  local slave_id = "marker_slave" .. lmark.slave_cookie
+  lmark.slave_cookie = lmark.slave_cookie + 1
+  return slave_id
+end
+
+function lmark.saveable_slave_table(slave)
+  local saveable = {
+    slave_id = slave.slave_id,
+    triggers = slave.triggers,
+    old_read = slave.old_read
+  }
+  return saveable
+end
+
+function lmark:master_trigger_fn(trigger_name, point, ...)
+  local old_trigger = self.slave_table.old_triggers[trigger_name]
+  -- Pull the trigger on the master first.
+  old_trigger(self, point, ...)
+
+  local slave_points =
+    dgn.find_marker_positions_by_prop("slave_id", self.slave_table.slave_id)
+  for _, slave_pos in ipairs(slave_points) do
+    old_trigger(self, slave_pos, ...)
+  end
+end
+
+function lmark:master_write(marker, th)
+  -- Save the slave table first.
+  lmark.marshall_table(th, lmark.saveable_slave_table(self.slave_table))
+  self.slave_table.old_write(self, marker, th)
+end
+
+
+function lmark:master_read(marker, th)
+  -- Load the slave table.
+  local slave_table = lmark.unmarshall_table(th)
+
+  local cookie_number = string.match(slave_table.slave_id, "marker_slave(%d+)")
+  -- [ds] Try to avoid reusing the same cookie as one we've reloaded.
+  -- This is only necessary to avoid collisions with cookies generated
+  -- for future vaults placed on this level (such as by the Trowel
+  -- card).
+  if cookie_number then
+    cookie_number = tonumber(cookie_number)
+    if lmark.slave_cookie <= cookie_number then
+      lmark.slave_cookie = cookie_number + 1
+    end
+  end
+
+  -- Call the old read function.
+  local newself = slave_table.old_read(self, marker, th)
+  -- And redecorate the marker as a master marker.
+  return lmark.make_master(newself, slave_table.slave_id,
+                           slave_table.triggers)
+end
+
+function lmark.make_master(lmarker, slave_id, triggers)
+  local old_trigger_map = { }
+  for _, trigger_name in ipairs(triggers) do
+    old_trigger_map[trigger_name] = lmarker[trigger_name]
+    lmarker[trigger_name] =
+      function (self, ...)
+        return lmark.master_trigger_fn(self, trigger_name, ...)
+      end
+  end
+
+  lmarker.slave_table = {
+    slave_id = slave_id,
+    triggers = triggers,
+    old_write = lmarker.write,
+    old_triggers = old_trigger_map,
+    old_read = lmarker.read
+  }
+
+  lmarker.write = lmark.master_write
+  lmarker.read = lmark.master_read
+
+  return lmarker
+end
+
+function lmark.make_slave(slave_id)
+  return portal_desc { slave_id = slave_id }
+end
+
+function lmark.synchronized_markers(master, ...)
+  local first = true
+  local slave_id = lmark.next_slave_id()
+  local triggers = { ... }
+  assert(#triggers > 0,
+         "Please provide one or more trigger functions on the master marker")
+  return function ()
+           if first then
+             first = false
+             return lmark.make_master(master, slave_id, triggers)
+           else
+             return lmark.make_slave(slave_id)
+           end
+         end
+end
\ No newline at end of file
diff --git a/crawl-ref/source/dat/clua/luamark.lua b/crawl-ref/source/dat/clua/luamark.lua
index 86b125a53c..10eb05945c 100644
--- a/crawl-ref/source/dat/clua/luamark.lua
+++ b/crawl-ref/source/dat/clua/luamark.lua
@@ -13,6 +13,7 @@ require('clua/lm_fog.lua')
 require('clua/lm_props.lua')
 require('clua/lm_monst.lua')
 require('clua/lm_func.lua')
+require('clua/lm_mslav.lua')
 
 function dlua_marker_function(table, name)
   return table[name]
@@ -28,7 +29,7 @@ function dlua_marker_read(fn, marker, th)
   return fn({ }, marker, th)
 end
 
-lmark = { }
+util.namespace('lmark')
 
 -- Marshalls a table comprising of keys that are strings or numbers only,
 -- and values that are strings, numbers, functions, or tables only. The table
diff --git a/crawl-ref/source/dat/clua/point.lua b/crawl-ref/source/dat/clua/point.lua
index b750372197..f186dc62f5 100644
--- a/crawl-ref/source/dat/clua/point.lua
+++ b/crawl-ref/source/dat/clua/point.lua
@@ -22,6 +22,10 @@ local function sgn(x)
   end
 end
 
+function point_metatable:xy()
+  return self.x, self.y
+end
+
 point_metatable.sgn = function (p)
                         return dgn.point(sgn(p.x), sgn(p.y))
                       end
diff --git a/crawl-ref/source/dat/clua/util.lua b/crawl-ref/source/dat/clua/util.lua
index 1ed3670172..5ef063d9fb 100644
--- a/crawl-ref/source/dat/clua/util.lua
+++ b/crawl-ref/source/dat/clua/util.lua
@@ -326,3 +326,11 @@ function util.copy_table(object)
   return _copy(object)
 end
 
+-- Initialises a namespace that has functions spread across multiple files.
+-- If the namespace table does not exist, it is created. If it already exists,
+-- it is not modified.
+function util.namespace(table_name)
+  if _G[table_name] == nil then
+    _G[table_name] = { }
+  end
+end
\ No newline at end of file
diff --git a/crawl-ref/source/dat/clua/ziggurat.lua b/crawl-ref/source/dat/clua/ziggurat.lua
index ba35595d70..8ac89bc460 100644
--- a/crawl-ref/source/dat/clua/ziggurat.lua
+++ b/crawl-ref/source/dat/clua/ziggurat.lua
@@ -600,7 +600,7 @@ local function ziggurat_create_loot_vault(entry, exit)
     return exit
   else
     -- Find the square to drop the loot.
-    local lootx, looty = dgn.find_marker_prop("ziggurat_loot")
+    local lootx, looty = dgn.find_marker_position_by_prop("ziggurat_loot")
 
     if lootx and looty then
       return dgn.point(lootx, looty)
diff --git a/crawl-ref/source/dat/volcano.des b/crawl-ref/source/dat/volcano.des
index fdfd592fe9..1b248e11ed 100644
--- a/crawl-ref/source/dat/volcano.des
+++ b/crawl-ref/source/dat/volcano.des
@@ -156,28 +156,28 @@ function place_large_volcano(e)
     e.kfeat("V = l")
     e.lua_marker('V', fog_machine { cloud_type = "flame", walk_dist=15, pow_max=6,
                                    delay = 300, size = 10000, spread_rate = 30,
-                                   helper = large_warning})
+                                   listener = large_warning})
 end
 
 function place_medium_volcano(e)
     e.kfeat("V = l")
     e.lua_marker('V', fog_machine { cloud_type = "flame", walk_dist=15, pow_max=6,
                                    delay = 300, size = 3000, spread_rate = 30,
-                                   helper = small_warning})
+                                   listener = small_warning})
 end
 
 function place_small_volcano(e)
     e.kfeat("V = l")
     e.lua_marker('V', fog_machine { cloud_type = "flame", walk_dist=15, pow_max=6,
                                    delay = 300, size = 800, spread_rate = 30,
-                                   helper = small_warning})
+                                   listener = small_warning})
 end
 
 function place_tiny_volcano(e)
     e.kfeat("V = l")
     e.lua_marker('V', fog_machine { cloud_type = "flame", walk_dist=10, pow_max=6,
                                    delay = 800, size = 80, spread_rate = 10,
-                                   helper = large_warning})
+                                   listener = large_warning})
 end
 
 function place_medium_flame_cloud (e, glyph, nolava)
@@ -389,6 +389,33 @@ default-depth: Lair:1-8, Orc:1-4, Hive:1
 
 ###############################################################################
 # Entries:
+
+# [ds] A dummy entry that's a proof-of-concept for synchronized fog machines
+# that trigger at multiple places at the same instant, but still have a random
+# delay.
+NAME: enter_volcano_snarktest101
+TAGS: uniq_volcano
+ORIENT: float
+WEIGHT: 0
+{{
+  local fog = fog_machine { cloud_type = 'flame',
+                            size = 3, pow_min=2,
+                            pow_max = 5, delay_min = 22, delay_max = 120,
+                          }
+  lua_marker('m', lmark.synchronized_markers(fog, 'do_fog'))
+}}
+SUBST: m = .
+:           volcano_portal(_G)
+MAP
+.......
+...m...
+.......
+.m.O.m.
+.......
+...m...
+.......
+ENDMAP
+
 NAME:       enter_volcano_1
 TAGS:       uniq_volcano
 ORIENT:     float
@@ -841,8 +868,8 @@ LFLAGS:     no_tele_control
 {{
 local mytable = { total_doorways=8, total_collapsed=0, ac = {} }
 
-local function collapse_doorways (marker, mytable)
-    local x, y = marker:pos()
+local function collapse_doorways (point, mytable)
+    local x, y = point:xy()
     local you_x, you_y = you.pos()
     if mytable.total_collapsed == mytable.total_doorways then
         return
@@ -856,7 +883,7 @@ local function collapse_doorways (marker, mytable)
     local ack = x .. "/" .. y
     if mytable.ac[ack] ~= true then
         mytable.ac[ack] = true
-        if you.see_cell(marker:pos()) then
+        if you.see_cell(x, y) then
             crawl.mpr("The volcano erupts! Nearby, a roof collapses.", "warning")
         else
             crawl.mpr("There is a rumble as the volcano erupts. The roof shakes.",
@@ -868,8 +895,14 @@ local function collapse_doorways (marker, mytable)
     end
 end
 
-local collapse_marker = function_machine ( {marker_type = "random", turns_min=30,
-                        turns_max=40, func=collapse_doorways, marker_params=mytable } )
+local collapse_marker = function_machine {
+  marker_type = "random",
+  turns_min=30,
+  turns_max=40,
+  func=collapse_doorways,
+  marker_params=mytable
+}
+
 }}
 KPROP:      RXZ12< = no_rtele_into
 SUBST:      X = .
diff --git a/crawl-ref/source/l_crawl.cc b/crawl-ref/source/l_crawl.cc
index d7571a63e7..a1682c59b3 100644
--- a/crawl-ref/source/l_crawl.cc
+++ b/crawl-ref/source/l_crawl.cc
@@ -603,7 +603,7 @@ void cluaopen_crawl(lua_State *ls)
 
 LUAFN(_crawl_args)
 {
-    return dlua_stringtable(ls, SysEnv.cmd_args);
+    return clua_stringtable(ls, SysEnv.cmd_args);
 }
 
 LUAFN(_crawl_milestone)
diff --git a/crawl-ref/source/l_dgn.cc b/crawl-ref/source/l_dgn.cc
index 86d142192e..180ffc87ab 100644
--- a/crawl-ref/source/l_dgn.cc
+++ b/crawl-ref/source/l_dgn.cc
@@ -356,7 +356,7 @@ static int dgn_map(lua_State *ls)
 {
     MAP(ls, 1, map);
     if (lua_gettop(ls) == 1)
-        return dlua_stringtable(ls, map->map.get_lines());
+        return clua_stringtable(ls, map->map.get_lines());
 
     if (lua_isnil(ls, 2))
     {
@@ -1407,12 +1407,12 @@ LUAFN(_dgn_in_vault)
     return (1);
 }
 
-LUAFN(_dgn_find_marker_prop)
+LUAFN(_dgn_find_marker_position_by_prop)
 {
     const char *prop = luaL_checkstring(ls, 1);
     const std::string value(
                             lua_gettop(ls) >= 2 ? luaL_checkstring(ls, 2) : "");
-    const coord_def place = find_marker_prop(prop, value);
+    const coord_def place = find_marker_position_by_prop(prop, value);
     if (map_bounds(place))
         clua_push_coord(ls, place);
     else
@@ -1423,6 +1423,36 @@ LUAFN(_dgn_find_marker_prop)
     return (2);
 }
 
+LUAFN(_dgn_find_marker_positions_by_prop)
+{
+    const char *prop = luaL_checkstring(ls, 1);
+    const std::string value(
+                            lua_gettop(ls) >= 2 ? luaL_checkstring(ls, 2) : "");
+    const unsigned limit(lua_gettop(ls) >= 3 ? luaL_checkint(ls, 3) : 0);
+    const std::vector<coord_def> places =
+        find_marker_positions_by_prop(prop, value, limit);
+    clua_gentable(ls, places, clua_pushpoint);
+    return (1);
+}
+
+static int _push_mapmarker(lua_State *ls, map_marker *marker)
+{
+    dlua_push_userdata(ls, marker, MAPMARK_METATABLE);
+    return (1);
+}
+
+LUAFN(_dgn_find_markers_by_prop)
+{
+    const char *prop = luaL_checkstring(ls, 1);
+    const std::string value(
+                            lua_gettop(ls) >= 2 ? luaL_checkstring(ls, 2) : "");
+    const unsigned limit(lua_gettop(ls) >= 3 ? luaL_checkint(ls, 3) : 0);
+    const std::vector<map_marker*> places =
+        find_markers_by_prop(prop, value, limit);
+    clua_gentable(ls, places, _push_mapmarker);
+    return (1);
+}
+
 extern spec_room lua_special_room_spec;
 extern int       lua_special_room_level;
 
@@ -1588,7 +1618,9 @@ const struct luaL_reg dgn_dlib[] =
 { "resolve_map", _dgn_resolve_map },
 { "in_vault", _dgn_in_vault },
 
-{ "find_marker_prop", _dgn_find_marker_prop },
+{ "find_marker_position_by_prop", _dgn_find_marker_position_by_prop },
+{ "find_marker_positions_by_prop", _dgn_find_marker_positions_by_prop },
+{ "find_markers_by_prop", _dgn_find_markers_by_prop },
 
 { "get_special_room_info", dgn_get_special_room_info },
 
diff --git a/crawl-ref/source/mapmark.cc b/crawl-ref/source/mapmark.cc
index 253855eb23..e7d3abf65a 100644
--- a/crawl-ref/source/mapmark.cc
+++ b/crawl-ref/source/mapmark.cc
@@ -824,16 +824,59 @@ bool feature_marker_at(const coord_def &pos, dungeon_feature_type feat)
     return (false);
 }
 
-const coord_def find_marker_prop(const std::string &prop,
-                                 const std::string &expected)
+coord_def find_marker_position_by_prop(const std::string &prop,
+                                       const std::string &expected)
 {
+    const std::vector<coord_def> markers =
+        find_marker_positions_by_prop(prop, expected, 1);
+    if (markers.empty())
+    {
+        const coord_def nowhere(-1, -1);
+        return (nowhere);
+    }
+    return markers[0];
+}
+
+std::vector<coord_def> find_marker_positions_by_prop(
+    const std::string &prop,
+    const std::string &expected,
+    unsigned maxresults)
+{
+    std::vector<coord_def> marker_positions;
     for (rectangle_iterator i(0, 0); i; ++i)
     {
         const std::string value =
             env.markers.property_at(*i, MAT_ANY, prop);
         if (!value.empty() && (expected.empty() || value == expected))
-            return (*i);
+        {
+            marker_positions.push_back(*i);
+            if (maxresults && marker_positions.size() >= maxresults)
+                return (marker_positions);
+        }
+    }
+    return (marker_positions);
+}
+
+std::vector<map_marker*> find_markers_by_prop(
+    const std::string &prop,
+    const std::string &expected,
+    unsigned maxresults)
+{
+    std::vector<map_marker*> markers;
+    for (rectangle_iterator pos(0, 0); pos; ++pos)
+    {
+        const std::vector<map_marker*> markers_here =
+            env.markers.get_markers_at(*pos);
+        for (unsigned i = 0, size = markers_here.size(); i < size; ++i)
+        {
+            const std::string value(markers_here[i]->property(prop));
+            if (!value.empty() && (expected.empty() || value == expected))
+            {
+                markers.push_back(markers_here[i]);
+                if (maxresults && markers.size() >= maxresults)
+                    return (markers);
+            }
+        }
     }
-    const coord_def nowhere(-1, -1);
-    return (nowhere);
+    return (markers);
 }
diff --git a/crawl-ref/source/mapmark.h b/crawl-ref/source/mapmark.h
index 71a142ce13..67e64a2804 100644
--- a/crawl-ref/source/mapmark.h
+++ b/crawl-ref/source/mapmark.h
@@ -13,6 +13,7 @@
 #include "dlua.h"
 #include <map>
 #include <string>
+#include <vector>
 #include <memory>
 
 //////////////////////////////////////////////////////////////////////////
@@ -23,8 +24,16 @@ class writer;
 
 bool marker_vetoes_operation(const char *op);
 bool feature_marker_at(const coord_def &pos, dungeon_feature_type feat);
-const coord_def find_marker_prop(const std::string &prop,
-                                 const std::string &expected = "");
+coord_def find_marker_position_by_prop(const std::string &prop,
+                                       const std::string &expected = "");
+std::vector<coord_def> find_marker_positions_by_prop(
+    const std::string &prop,
+    const std::string &expected = "",
+    unsigned maxresults = 0);
+std::vector<map_marker*> find_markers_by_prop(
+    const std::string &prop,
+    const std::string &expected = "",
+    unsigned maxresults = 0);
 
 class map_marker
 {