Allocate Lua PenArray objects using an existing buffer

library/LuaApi.cpp

@@ -1064,7 +1064,8 @@ static int dfhack_penarray_new(lua_State *L)
 {
     int bufwidth = luaL_checkint(L, 1);
     int bufheight = luaL_checkint(L, 2);
-    new (L) PenArray(bufwidth, bufheight);
+    void *buf = lua_newuserdata(L, sizeof(PenArray) + (sizeof(Pen) * bufwidth * bufheight));
+    new (buf) PenArray(bufwidth, bufheight, buf);
 
     lua_rawgetp(L, LUA_REGISTRYINDEX, &DFHACK_PENARRAY_TOKEN);
     lua_setmetatable(L, -2);

library/include/LuaTools.h

@@ -48,7 +48,6 @@ namespace DFHack {
     }
     namespace Screen {
         struct Pen;
-        struct PenArray;
     };
 }
 

library/include/modules/Screen.h

@@ -118,8 +118,10 @@ namespace DFHack
             Pen *buffer;
             unsigned int dimx;
             unsigned int dimy;
+            bool static_alloc;
         public:
             PenArray(unsigned int bufwidth, unsigned int bufheight);
+            PenArray(unsigned int bufwidth, unsigned int bufheight, void *buf);
             ~PenArray();
             void clear();
             void set_tile(unsigned int x, unsigned int y, Screen::Pen pen);

library/modules/Screen.cpp

@@ -442,15 +442,23 @@ df::interface_key Screen::charToKey(char code)
  */
 
 PenArray::PenArray(unsigned int bufwidth, unsigned int bufheight)
-    :dimx(bufwidth), dimy(bufheight)
+    :dimx(bufwidth), dimy(bufheight), static_alloc(false)
 {
     buffer = new Pen[bufwidth * bufheight];
     clear();
 }
 
+PenArray::PenArray(unsigned int bufwidth, unsigned int bufheight, void *buf)
+    :dimx(bufwidth), dimy(bufheight), static_alloc(true)
+{
+    buffer = (Pen*)((uint8_t*)buf + sizeof(PenArray));
+    clear();
+}
+
 PenArray::~PenArray()
 {
-    delete[] buffer;
+    if (!static_alloc)
+        delete[] buffer;
 }
 
 void PenArray::clear()