Hey,

I am currently using LuaBridge as the C++ interface to Lua, and I'm having trouble passing a simple pointer to Lua (as a unique identifier for an object) and then back again. The Lua script calls "object(...)" which returns a pointer, and the pointer is stored in a local: "local obj = tbl.object(....)". If I then proceed to use the variable obj for anything, it's always "nil". What's going on here?

I would think this was the most basic and repeating pattern in Lua scripting to use memory addresses as identifiers as well as simplify access to engine internals.

static Object* object(int x, int y, int w, int h, int floor) {
  auto obj = std::make_unique<Object> (gworld(), x, y, w, h, floor);
  gworld().objects().add(std::move(obj));
  return obj.get();
}
...
static void object_frame(LuaRef id, int tex, int x, int y, int w, int h) {
  printf("object_frame(%p, tex=%d)\n", id.cast<Object*> (), tex);
}
...
  gns.beginNamespace("dm")
    .addFunction("object", object)
...
  local obj = dm.object(x,y, 8,8, 0)
  dm.object_frame(obj, gui.tex, 80 + 9*idx,0, 9,8)

The value of id, which should just be a memory address, in the "object_frame" function is always nil.

I solved this, for now, by passing uintptr_t around. Thought about putting the objects index into the 16 unused address bits, but I haven't needed it yet.

It's very strange though, that LuaBridge can't pass even void* around. I would understand it if it tried to translate objects (I've seen the more complex usage), but void* should just be passed around as an opaque pointer, which is what it was designed as. Disappointing too.

And why am I not Prime Members anymore

On 19.6.2017 at 9:32 AM, Daixiwen said:

Did you also register your Object class in LuaRef? In your beginNamespace() you must have somewhere at least a .beginClass<Object>("Object") somewhere before the LuaRef can be casted to the Object class.

I actually haven't tried that interface yet. All I wanted to do was pass a memory address to Lua, which Lua should interpret as opaque and just pass back as parameters to my engine interface.

I will probably try the class-like method at some point and see how useful it is.