Access CPP global via Lua?

[Driklyn]

Started with a CPP project, but using Lua for scripted objects. Need to be able to access things like:

 

window->KeyDown
window->SetMousePosition
world->gravity

 

...from within the scripts themselves, even though they are defined in a CPP header file (App.h).

 

How exactly do I access them?

[AggrorJorn]

Every C++ command has a Lua equivalent (or better said: the Lua function refers to the C++ command):

http://www.leadwerks.com/werkspace/page/documentation/_/command-reference/window/windowmousehit-r457

 

Every command is documented with C++ as well as Lua.

[Driklyn]

Yes, I realize this, but I'm not creating the window/world in a script, as is occurring when you start from a Lua project. I need to be able to access the already created window/world (in CPP) via a script.

 

I was thinking I might need to use the `Interpreter` class, but I'm not entirely sure how to.

[Josh]

Writing Lua interfaces is beyond the scope of what Leadwerks provides support for. However, the Interpreter class contains an analog for nearly every Lua C++ command and can be used to push and pop things from the Lua stack. I believe it would be something like this:

Interpreter::PushString("hello");
Interpreter::SetGlobal("myvar");

 

Whenever you are doing stack manipulation, it's a good idea to start a block of code with this:

int stacksize = Interpreter::GetStackSize();

 

And end it with this:

Interpreter::SetStackSize(stacksize);

 

This will ensure you don't mess up the stack inadvertently, and it's easier than popping a bunch of values yourself.

 

For full C++ binding with Lua, I recommend ToLua++:

http://www.leadwerks.com/werkspace/files/file/216-tolua/

[Driklyn]

Thank you, Josh. Finally got it working! (I had nearly exactly what you wrote before creating this topic, but I placed SetGlobal before PushObject.)

 

bool App::Start() {
   // create window, context, world...

   int stacksize = Interpreter::GetStackSize();
   Interpreter::PushObject(window);
   Interpreter::SetGlobal("window");
   Interpreter::PushObject(context);
   Interpreter::SetGlobal("context");
   Interpreter::PushObject(world);
   Interpreter::SetGlobal("world");
   Interpreter::SetStackSize(stacksize);

   // load map, etc...
}

 

Then, from any script:

 

function Script:Start()
   System:Print(context:GetWidth())
   System:Print(context:GetHeight())
   System:Print(world.gravity) -- prints 0x00000000

   window:ShowMouse()
end

function Script:UpdateWorld()
   if window:KeyDown(Key.D) then
       System:Print("D down")
   end
end

 

This is awesome! And was much easier to do than expected... Only hiccup is that I couldn't seem to access any members of `world`, just its methods. I did, however, figure out you can do it this way instead:

 

Interpreter::PushObject(&world->gravity);
Interpreter::SetGlobal("worldGravity");

 

worldGravity.y = worldGravity.y * -1

[Josh]

Lua docs:

http://www.lua.org/manual/5.1/

 

Like I said, most Lua commands have a method in the Interpreter class, but if not you can get the Lua virtual machine with Interpreter::L and start calling Lua yourself directly. Have fun!

[shadmar]

Hey this is nice!