CSE 380 – Computer Game Programming Scripting and Lua Lua

What is a scripting language? A higher-level programming language (of sorts) Interpreted by another program at runtime –like a game engine Hardware Machine Code Assembly Code High-Level Language Code Scripting Language Code

The first one? SCUMM Script Creation Utility for Maniac Mansion –by LucasArts for Commodore 64

What’s the point? NO MORE CONSTANTS –Why? –What’s wrong with constants? They’re simpler languages –So? –Doesn’t more languages mean more complexity? Programming for non-programmers Compiler-time liberated development Tools + Scriping

And for games? Make Mods or Original Games Use scripts to specify: –Game Settings –GUI layout –Audio cues –Control bots –Responses to game events Bottom Line: –leave the heavy lifting to the engine. How? tap into engine via premade script functions & data

2 Scripting Flavors Data definition languages –declarative statements –used at game or level load time Runtime languages –code executes within engine context at runtime –extend or customize engine –allows for more complex instructions worldWidth:800 function process act(act) for i, act in ipairs(act) do if act:is_alive() then act.process() end

Typical Properties of Game Scripting Languages Interpreted Lightweight Support for rapid iteration Convenience/Ease of use Good for Rapid Prototyping

Popular Game Scripting Languages Game Engine –QuakeC –UnrealScript General Purpose –python –Lua

A crash course in Lua Let’s learn some simple stuff –Commenting –Variables –Operators –Functions –Tables –Conditional Statements –Iteration Download LuaExample.zip and open Ref:

A note about Lua Lua is a C library Using it in a C++ program can be tricky –structs instead of objects –global methods –unsupported C functions An alternative is LuaPlus –not standard Lua –you could write your own wrapper classes as well

Lua Commenting For single line, start line with “--” –Ex: -- THIS IS A COMMENT To span multiple lines: –open with --[[ –close with ]]-- –Ex: --[[ THIS IS A COMMENT --]]

Lua Variables Dynamically typed. Huh? –they can change type x = 3-- x is an integer x = x is a float x = "PI"-- x is a String A Lua variable can be a: –number, string, boolean, table, function, nil, userdata, or thread –nil ≈ NULL also marks variable for deletion Default scope for Lua variables is global

Lua Operators Many the regular suspects –like +, -, *, /, %, =, ==,, = Some you may not have used before, like: ^ for exponentiation ~= for testing for inequality.. for string concatenation And some are missing –like ++, --, +=, -=, *=, /= And some are done via keywords –Like and, or, and not

Lua Functions First class objects. Huh? –Can be treated like any other variable passed as a method argument assigned to a variable Function Declaration Example: function Square(val) return val * val end Function Invocation Example: x = Square(5)-- invoke our function print(x)-- prints 25

Lua Tables Lua’s only data structure Arrays and generic dictionaries all in one. Ex: prime = {2, 3, 5, 7, 11 } -- make a table print(prime[2]) -- access an element, print 5 prime[2] = assign a value Tables can be indexed by other types. Ex: idTable = {}-- make a table idTable["id1"] = put a num in idTable["id2"] = and another Table is actually either an array or a map

Lua Conditionals Support for if … elseif … else Ex: if x == 5 then print(5) elseif x == 6 then print(5) print(6) else print(0) end How does it know when one code block ends and another begins?

Lua Iteration Support for while and for statements Ex: prime = {2, 3, 5, 7, 11} for index, value in ipairs(prime) do print(index, value) end Nested Example: for i = 1, 10, 1 do if (i % 2) == 2 then print(i) end

C++  Lua and Lua  C++ We may need to do both Tricky with C++. Why? –Lua is in C. Solution: Use LuaPlus –C++ library for interfacing with Lua –Not Lua standard Wed: –LuaPlus hands on examples –C++  LuaPlus –LuaPlus  C++ –How and why to do so

Reference Game Engine Architecture by Jason Gregory –Chapter 14: Runtime Gameplay Foundation Systems Game Coding Complete, 4 th Edition by Mike McShaffry and David Graham –Chapter 12: Scripting with Lua