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Let's make a game for the Playdate
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- 13. BriefintrotoLua Luaisadynamicallytypedlanguage Therearenotypedefinitionsinthelanguage,eachvaluecarriesitsowntype Primitives "Hello world" -- string 10.4 -- number true -- boolean nil -- nil print -- function 13
- 14. Functions Functionscanbothcarryoutaspecifictaskorcomputeandreturnvalues function add(a, b) return a + b end print(add(10, 20)) -- Returns 30 Inthatsyntax,afunctiondefinitionhasaname(add),alistofparameters(aandb), andabody,whichisalistofstatements 14
- 15. Tables Thetabletypeareassociativearrays AssociativearraysaresimilartoPHParraysorJavascriptobjects,theyarekey/value containersthatcanalsobeusedaslists Tableshavenofixedsize,youcanaddasmanyelementsasyouwanttoatable dynamically -- Create a table and store its reference in `player' player = {} player["hp"] = 100 print(player["hp"]) -- Prints 100 print(player.hp) -- Prints 100 (Same as above) 15
- 16. Tables Eachtablemaystorevalueswithdifferenttypesofindicesanditgrowsasitneedsto accommodatenewentries a = {} a[10] = "Hello" a["x"] = "World" print(a[10]) -- Prints "Hello" print(a.x) -- Prints "World" print(a[20]) -- Prints nil (undefined) Tablefieldsevaluatetoniliftheyarenotinitialized 16
- 17. Loops -- A numeric for has the following syntax for i = 1, 5 do print(i) end -- Output: -- 1 -- 2 -- 3 -- 4 -- 5 Watchout:InLua,indicesstartsat1(ugh!) 17
- 18. Loops ThebasicLualibraryprovidespairs,ahandyfunctionthatallowsyoutoiterateover theelementsofatable a = {} a[10] = "Hello" a["x"] = "World" for key, value in pairs(a) do print(key .. " - " .. value) -- Concats strings with .. end -- Output: -- 10 - Hello -- x - World 18
- 19. Conditionals -- If statements are not so different from other languages if a < 0 then a = 0 end -- If else statement if a < b then return a else return b end -- But I personally prefer the inlined style if a < b then return a else return b end 19
- 20. Scoping InLua,everyvariableisglobalbydefault(uselocaltoavoidconflicts,overridingandbugs) a = 0 -- Global scope local b = 0 -- Local scope do -- New scope (can be a function, a loop, etc) a = 5 b = 5 local c = 5 end print(a) -- Prints 5 print(b) -- Prints 0 print(c) -- Prints nil 20
- 21. LoadingaSprite -- Importing Playdate core libs import "CoreLibs/graphics" import "CoreLibs/sprites" gfx = playdate.graphics -- Shortcut to gfx library player = gfx.sprite:new() -- Creates a new sprite object player:setImage(gfx.image.new('player')) -- 'player.png' is being loaded player:moveTo(200, 120) -- Moving the sprite in the center player:addSprite() -- Adds the sprite to the display list function playdate.update() gfx.sprite.update() -- Calls update() on every sprite end 21
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- 23. -- Make the player sprite five time bigger player:setScale(5) 23
- 24. -- Rotating a sprite (in degrees) player:setRotation(135) 24
- 25. -- Flipping a sprite (on the horizontal side) player:setImageFlip(gfx.kImageFlippedX) 25
- 26. TransformingaSprite -- Setting the z-index for the sprite (high value = draw first) player:setZIndex(10) -- Sprites that aren’t visible don’t get their draw() method called player:setVisible(false) Formoresprite-relatedmethodshavealookattheirInsidePlaydatesection 26
- 27. Movingasprite function playdate.leftButtonDown() player:moveTo(player.x - 10, player.y) -- Player is moving to the left end function playdate.rightButtonDown() player:moveTo(player.x + 10, player.y) -- Player is moving to the right end function playdate.upButtonDown() player:moveTo(player.x, player.y - 10) -- Player is moving up end function playdate.downButtonDown() player:moveTo(player.x, player.y + 10) -- Player is moving down end 27
- 28. UsingtheCrank Forplaydate.cranked(),changeistheanglechangeindegrees acceleratedChangeischangemultipliedbyavaluethatincreasesasthecrank movesfaster,similartothewaymouseaccelerationworks -- Moves player horizontally based on how you turn the crank function playdate.cranked(change, acceleratedChange) player:moveTo(player.x + change, player.y) end 28
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- 30. OOP Luadoesnotofferbuilt-insupportforobject-orientedprogrammingofanykind CoreLibsprovidesabasicobject-orientedclasssystem Objectisthebaseclassallnewsubclassesinheritfrom -- Base class is Animal class('Animal').extends() -- Cat is a subclass of Animal class('Cat').extends(Animal) 30
- 31. OOP Classesareprovidedwithaninitfunction Thesubclassdecideshowmanyandwhattypeofargumentsitsinitfunctiontakes function Cat:init(age, weight) Cat.super.init(self, age) self.weight = weight end Theinitfunctionwillcallitssuperclass’simplementationofinit 31
- 32. OOP Let'smakeanexamplebyputtingtheplayerlogicinitsclass -- player.lua import "CoreLibs/graphics" import "CoreLibs/sprites" gfx = playdate.graphics class("Player").extends(gfx.sprite) function Player:init(x, y) Player.super.init(self) self:setImage(gfx.image.new('player')) self:moveTo(x, y) self:addSprite() end 32
- 33. OOP Looksbetternow,don'tyouthink? import "CoreLibs/graphics" import "CoreLibs/sprites" import "player" -- We need to import the player file gfx = playdate.graphics player = Player(200, 120) function playdate.update() gfx.sprite.update() end 33
- 34. players = { Player(100, 120), Player(200, 120), Player(300, 120) } 34
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