Löve and Lua
based on http://nova-fusion.com/2011/06/14/aguide-to-getting-started-with-love2d/
Löve
• 2D game framework
• simple to use
• free
Game Structure
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a folder with main.lua, other files
to distribute, just create a zip file of the
directory contents, and give the zip file a
.love extension:
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cd humpy
zip -r ../humpy.love *
... then you can double click the .love file
to run it
Löve’s API
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the “love” module is a Lua table, containing
the various other modules (also tables)
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audio,image,graphics,mouse,
keyboard,physics,etc.
many modules contain classes, eg Image
callbacks are defined in the love module
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let your program handle events, draw, update,etc
you don’t have to define all of them, just the ones
you need (exist default versions of each (most do
nothing))
callbacks in love
module
• love.load() -- one-time setup
• love.draw() -- to render the frame
• love.update() -- to update simulation
• love.mousepressed(),
love.mousereleased()
• love.run() -- main loop
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~tebo/4849/Love/simple
function love.update(dt)
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player.x = player.x + player.vx * dt
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player.y = player.y + player.vy * dt
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end
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function love.draw()
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love.graphics.print( tostring(player.vx), 300,200 )
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love.graphics.print( tostring(player.vy), 350,200 )
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love.graphics.draw ( image, player.x, player.y)
love.graphics
• for drawing lines, shapes, text
• Image and Drawable objects
• reading images and fonts
• managing framebuffer
• special objects like particle systems
screen coordinates
Points
•love.graphics.point ( x, y ) --draws a point
•love.graphics.setPointSize ( size )
•love.graphics.setPointStyle ( style )
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for i=1, max_stars do
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local x = math.random( 5, love.graphics.getWidth()-5)
~tebo/4849/Love/stars
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local y = math.random( 5, love.graphics.getHeight()-5)
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stars[i] = {x, y}
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end
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love.graphics.setPointSize ( 3 )
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love.graphics.setPointStyle ( "smooth" )
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end
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function love.draw()
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for i=1, #stars do -- loop through all of our stars
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love.graphics.point( stars[i][1], stars[i][2]) -- draw each
point
Lines
• love.graphics.line ( x1,y1, x2, y2, ... )
• love.graphics.line (table_of_points)
• love.graphics.setLineWidth ( w )
• love.graphics.setLineStyle ( style )
• function love.load()
~tebo/4849/Code/Love/lines
• points = { 0, 0 }
• end
• function love.draw()
• x, y = love.mouse.getPosition()
• love.graphics.setColor ( 255, 0, 0 )
• love.graphics.line ( 320, 240, x, y )
• points[#points + 1] = x
• points[#points + 1] = y
• love.graphics.setColor ( 0, 255, 0 )
• love.graphics.line ( points )
• end
Drawables
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drawable = love.graphics.newImage ( “filename” )
drawable = love.graphics.newParticleSystem ()
love.graphics.draw( drawable, x, y, r, sx, sy, ox, oy )
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function love.load()
~tebo/4849/Code/Love
/flyeye
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skyeye = love.graphics.newImage("masonic-eye.jpg")
width = skyeye:getWidth()
height = skyeye:getHeight()
angle = 0
rotvel = 10
end
function love.update(dt)
angle = angle + rotvel * dt
end
function love.draw()
love.graphics.draw( skyeye, 100, 100, math.rad(angle), 1, 1, width / 2,
height / 2)
love.audio
• ‘Source’ object -- can be played
• use OpenAL (directional sources,
listener)
• (not working on mac???)
• sounds are “static” (in RAM) or “stream”
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listener.x = 320
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listener.y = 240
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listener.angle = 0
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noisy
sound = love.audio.newSource("bing.wav", "static") -- the "static" tells LÖVE to load the file into
memory, good for short sound effects
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sound:setDirection( 0, 1, 0 ) -- "down"
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-- setup listener (not working on macosx at least)
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love.audio.setOrientation ( 0,-1,0, 0,0,1 ) -- forward and up vectors
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love.audio.setPosition ( listener.x, listener.y, 0 )
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love.audio.setVelocity ( 0, 100, 0 )
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end
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function love.mousepressed( x, y, button )
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sound:stop()
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-- set source position (doesn't seem to work on macosx?)
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sound:setPosition ( x, y, 0 )
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sound:setPitch ( y / 240.0 )
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sound:setVolume ( x / 320.0 )
Lua
• can run under embedding application
(Love)
• can run standalone (lua)
• good for experimenting, learning
chunks
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sequence of lua statements
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needs no separator between consecutive
statements
line breaks ignored
can be read from interactive console
can be read from a file
both: lua -i filename
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starts up console after running chunk from
filename
identifiers
• string of letters, digits, underscores
• starts with letter or underscore
• dont’ use names like _VERSION
• case sensitive
• dont use reserved words:
• and end break in repeat while false
local return do for nil then else
function not true elseif if or until
comments
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single line comment: starts with -- (2
hyphens)
block comments
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--[[
--]]
(disable by adding a hyphen at front of
opening comment ---[[ is just a single line
comment)
Types and Values
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Lua is dynamically typed
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no type definitions
each value carries a type
8 basic types:
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nil, boolean, number, string, userdata, function,
thread, table
the type() function returns a string with the type’s name
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print( type(“Hello World”) )
print ( type(10.4*3))
Nil
• a type with a single value, nil
• a “non-value” meaning “no useful
value”
• different from every other value
• globals are nil by default (before
assignment)
• delete a variable by assigning nil to it
• return nil
Booleans
• two values: true and false
• conditionals consider nil and false as
false
• anything else (including 0, “”) is true
Numbers
• double-precision floating-point
• no rounding errors with integers <
10^14
• ex) 4
3.1543 6.25e23 100e-3
Strings
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sequence of characters
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can contain any embedded code, incl zero
immutable - can’t change strings, just create new ones with
changes
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a = “one string”
b = string.gsub(a, “one”, “another”0
print (a)
print (b)
can use single or double quotes
can include C-like escape sequences (\n, \t, etc)
can also use [[ and ]] to delimit multi-line strings
strings
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any numeric operation applied to a string tries to convert the string to a
number
print (“10” + 1) -- prints 11
if a number is given when a string is expected, lua tries to convert it
print(10 .. 20 ) -- prints 1020
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.. operator is string concatenation
best to do explicit coercion
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tonumber(string)
tostring(number)
get string length with the length operator, #
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a = “hello”
print(#a)
Tables
• associative arrays -- indexed with any
value except nil
• the ONLY data structure in lua
• used for arrays, sets, records, queues,
etc.
• tables are objects
table examples
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a = {} -- creates an empty table
k = “x”
a[k] = 10
a[20] = “cool”
print(a[“x”])
--> 10
k = 20
--> “cool”
print(a[k])
a[“x”] = a[“x”] + 1
print(a[“x”])
--> 11
tables
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tables grow as needed to hold new values
a.name is syntactic sugar for a[“name”]
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not a[name] !!!
lua convention: arrays start at 1!
# gives last index (size) of table (doesn’t count
holes...)
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for i = 1,#a do
print (a[i])
end
functions
• first-class values
• can store in variables,
• can pass as arguments to other
functions
• can be returned from functions
• “proper lexical scoping” of nested
functions
userdata and threads
• userdata - for arbitrary C data in lua
variables
• threads - coroutines(?)