dragonruby-lua

dragonruby-lua adds a native Lua VM to DragonRuby.

It lets DragonRuby call Lua functions, evaluate Lua strings, and read values from Lua.

You can even call DragonRuby C APIs with LuaJIT's ffi:

dragon = require('dragon') -- load dragon.lua from your project directory
ffi = require('ffi')

dragon.drb_log_write("Lua", 1, "Hello from Lua!")

local pixels = ffi.new('uint32_t[?]', 256*256)
for i=0,#pixels do
  pixels[i] = 0xff00ff00 -- green, full alpha
end

dragon.drb_upload_pixel_array('my_lua_pixels', 256, 256, pixels)

It is a fork of mruby-lua. Thank you to the author 🥳.

Dependencies

• libluajit (recommended) - headers, static library (-fPIC), or
• liblua5.2 (or newer) - headers, static library (-fPIC)

Tested with DragonRuby 3.18 on Linux.

The original author could compile with MinGW32 on Windows 7.

Hopefully it compiles easily elsewhere.

Compile Lua/LuaJIT with -fPIC

To combine with this code into a shared library, the compiler needs a static build of liblua or libluajit, with Position Independent Code.

The official releases are not built that way, so you must compile Lua/LuaJIT yourself.

Luckily, it is relatively quick and painless.

For Linux, I cloned lua/lua / LuaJIT, added '-shared -fPIC' to CFLAGS in their Makefiles, then ran make -j4.

A copy of the resulting liblua.a and libluajit.a for Linux x86_64 is included in this repo.

Ruby API

Lua

Class methods

• new -> Lua
  • Create instance of the Lua script engine.

Instance methods

• dostring(script_string) -> Hash|NilClass|TrueClass|FalseClass|Numeric|String

  • Run Lua script from string object. Return value converted to a Ruby object if possible.

• run(script_string)

  • Alias for dostring.

• << script_string

  • Alias for dostring.

      lua << 'io.write("Hello from Ruby")'
      lua << <<~LUA
        function hello_world(name)
          io.write("Hello " .. (name or "World"))
        end
      LUA

• dofile(script_file_path) -> nil

  • Run Lua script from file.

• [key] -> object, [key] = object

  • Get or set global variable.

• call_global(name, arg1=nil, .., arg9=nil) -> Hash|NilClass|TrueClass|FalseClass|Numeric|String

  • Calls a global Lua function by name, with up to 9 arguments.
    • Faster than dostring("foo(1, 2, 3)").
    • Arguments converted safely.

Note about VS Code

If you use heredocs with LUA as the token, then VS Code will highlight the contents as Lua ;-)

lua.run(<<~LUA)
  function beautiful_highlighted_lua(code)
    yes:please()
  end
LUA

lua << <<~LUA
  look:ma("it's some", "highlighted", "Lua")
END

Supported data convertion

MRuby type	To Lua	From Lua	Lua type
Nil	o	o	NIL
Fixnum	o	o	NUMBER
Float	o	o	NUMBER
String	o	o	STRING
array			TABLE
hash		o	TABLE
C pointer		o	FUNCTION(c)
-			FUNCTION
Exception			-
Bool	o	o	BOOLEAN
-			USERDATA
-			LIGHTUSERDATA
-			THREAD

Examples from mruby-lua

Lua#dostring method

lua = Lua.new

script =<<"EOF"
  function twice(x)
    return x * 2
  end
  a = 10
  b = 20
  print(a * twice(b))
EOF

lua.dostring script
  => 400

Lua#dofile method

lua = Lua.new
lua.dofile "test/fib.lua"

Lua#[] method

Get global variable from Lua.

lua = Lua.new

lua.dostring "a = 10; b = 20; c = a * b"

p lua["a"] # => 10
p lua["b"] # => 20
p lua["c"] # => 200

lua.dostring "vec1 = { x = 0.0, y = 1.0, z = 3.0 }"
p lua["vec1"]
# => {"x"=>0, "y"=>1, "z"=>3}

Lua#[]= method

Set global variable to Lua.

lua = Lua.new

lua["a"] = 123
lua["b"] = 23.45
lua["c"] = true
lua["d"] = nil

lua.dostring "print(a)" # => 123
lua.dostring "print(b)" # => 23.45
lua.dostring "print(c)" # => true
lua.dostring "print(d)" # => nil