# Lua Scripting Interface

## Introduction

MAME provides Lua script bindings for a useful set of core functionality. This feature first appeared in version 0.148, when a minimal Lua interface was implemented. Today, the Lua interface is rich enough to let you inspect and manipulate device state, access CPU registers, read and write memory, and draw custom graphical overlays.

There are three ways to use MAME’s Lua scripting capabilities:

- Using the interactive Lua console, enabled by the console option.

- By providing a script file to run using the -autoboot_script option. The -autoboot_delay option controls how long MAME waits after starting the emulated system before running the script.

- By writing Lua plugins. Several plugins are included with MAME.

Internally, MAME makes extensive use of Sol3 to implement Lua bindings.

The Lua API is not yet declared stable and may suddenly change without prior notice. However, we expose methods to let you know at runtime which API version you are running against, and most objects support some level of runtime introspection.

## Features

The API is not yet complete, but this is a partial list of capabilities exposed to Lua scripts:

- Session information (application version, current emulated system)

- Session control (starting, pausing, resetting, stopping)

- Event hooks (on frame painting and on user events)

- Device introspection (device tree listing, memory and register enumeration)

- Screen introspection (screens listing, screen details, frame counting)

- Screen overlay drawing (text, lines, boxes on multiple screens)

- Memory read/write (8/16/32/64 bits, signed and unsigned)

- Register and state control (state enumeration, get and set)

## API reference

- Lua Common Types and Globals
  - Containers
  - Emulator interface
- Lua Core Classes
  - Notifier subscription
  - Attotime
  - MAME machine manager
  - Running machine
  - Video manager
  - Sound manager
  - Output manager
  - Parameters manager
  - UI manager
  - System driver metadata
  - Lua plugin
- Lua Device Classes
  - Device enumerators
  - Device
  - Palette device
  - Screen device
  - Vector device
  - Cassette image device
  - Image device interface
  - Sound device interface
  - Slot device interface
  - Device state entry
  - Media image format
  - Slot option
- Lua Memory System Classes
  - Memory manager
  - Address space
  - Pass-through handler
  - Address map
  - Address map entry
  - Address map handler data
  - Memory share
  - Memory bank
  - Memory region
- Lua Input System Classes
  - I/O port manager
  - Natural keyboard manager
  - Keyboard input device
  - I/O port
  - I/O port field
  - Live I/O port field state
  - Input type
  - Input manager
  - Input code poller
  - Input sequence poller
  - Input sequence
  - Host input device class
  - Host input device
  - Host input device item
  - UI input manager
- Lua Render System Classes
  - Render bounds
  - Render colour
  - Palette
  - Bitmap
  - Render texture
  - Render manager
  - Render target
  - Render container
  - Container user settings
  - Layout file
  - Layout view
  - Layout view item
  - Layout element
- Lua Debugger Classes
  - Symbol table
  - Parsed expression
  - Symbol entry
  - Debugger manager
  - Device debugger interface
  - Breakpoint
  - Watchpoint
  - Expression error

## Interactive Lua console tutorial

First run an arcade game in MAME at the command prompt with the `-console` and `-window` options to enable the Lua console:

    $ mame -console -window YOUR_SYSTEM
           /|  /|    /|     /|  /|    _______
          / | / |   / |    / | / |   /      /
         /  |/  |  /  |   /  |/  |  /  ____/
        /       | /   |  /       | /  /_
       /        |/    | /        |/  __/
      /  /|  /|    /| |/  /|  /|    /____
     /  / | / |   / |    / | / |        /
    / _/  |/  /  /  |___/  |/  /_______/
             /  /
            / _/

    mame 0.255
    Copyright (C) Nicola Salmoria and the MAME team

    Lua 5.4
    Copyright (C) Lua.org, PUC-Rio

    [MAME]>

At this point, your game is probably running in attract mode. Let’s pause it:

    [MAME]> emu.pause()
    [MAME]>

Even without textual feedback on the console, you’ll notice the game is now paused. In general, commands are quiet and only print error messages.

You can check the version of MAME you are running with:

    [MAME]> print(emu.app_name() .. " " .. emu.app_version())
    mame 0.255

Let’s examine the emulated screens. First, enumerate the screen devices in the system:

    [MAME]> for tag, screen in pairs(manager.machine.screens) do print(tag) end
    :screen

`manager.machine` is the running machine object for the current emulation session. We will be using this frequently. `screens` is a device enumerator that yields all emulated screens in the system. Most arcade games only have one main screen. In our case, the main and only screen has the absolute tag `:screen`. We can examine it further:

    [MAME]> -- keep a reference to the main screen in a variable
    [MAME]> s = manager.machine.screens[':screen']
    [MAME]> print(s.width .. 'x' .. s.height)
    320x224

Several methods are available for drawing an overlay on the screen using lines, rectangles and text:

    [MAME]> -- define a function for drawing an overlay and call it
    [MAME]> function draw_overlay()
    [MAME]>> s:draw_text(40, 40, 'foo') -- (x0, y0, msg)
    [MAME]>> s:draw_box(20, 20, 80, 80, 0xff00ffff, 0) -- (x0, y0, x1, y1, line-color, fill-color)
    [MAME]>> s:draw_line(20, 20, 80, 80, 0xff00ffff) -- (x0, y0, x1, y1, line-color)
    [MAME]>> end
    [MAME]> draw_overlay()

This will draw some useless lines and text over the screen. However, when the emulated system is resumed, your overlay needs to be refreshed or it will just disappear. In order to do this, you have to register your function to be called on every video update:

    [MAME]> emu.register_frame_done(draw_overlay, 'frame')

All colors are specified in ARGB format (eight bits per channel). The coordinate origin (0,0) normally corresponds to the top-left corner of the screen.

As with screens, you can examine all the emulated devices in the running system:

    [MAME]> for tag, device in pairs(manager.machine.devices) do print(tag) end
    :audiocpu
    :maincpu
    :saveram
    :screen
    :palette
    [...]

For some of them, you can also inspect and manipulate memory and state:

    [MAME]> cpu = manager.machine.devices[':maincpu']
    [MAME]> -- enumerate, read and write register state
    [MAME]> for k, v in pairs(cpu.state) do print(k) end
    CURPC
    rPC
    IR
    CURFLAGS
    SSR
    D0
    [...]
    [MAME]> print(cpu.state["D0"].value)
    303
    [MAME]> cpu.state['D0'].value = 255
    [MAME]> print(cpu.state['D0'].value)
    255

    [MAME]> -- inspect memory
    [MAME]> for name, space in pairs(cpu.spaces) do print(name) end
    program
    cpu_space
    [MAME]> mem = cpu.spaces['program']
    [MAME]> print(mem:read_i8(0xc000))
    41

Note that many objects support symbol completion if you type part of a method or property name and press the Tab key:

    [MAME]>print(mem:read_<TAB>
    read_direct_i8
    read_u16
    read_range
    read_direct_u16
    read_direct_i64
    read_i64
    read_i32
    read_direct_u64
    read_i8
    read_u32
    read_u8
    read_u64
    read_direct_u32
    read_direct_i16
    read_direct_i32
    read_direct_u8
    read_i16
    [MAME]>print(mem:read_direct_i8