A step by step tutorial for Asteroids written in Codea aimed at beginners. I would recommend looking at the Noob Lander and Snake tutorial before this one if you haven't done any coding before. In fact, this tutorial builds on the first few steps of the Snake tutorial. Also there is more involved in each step and the comments are less line by li…

Asteroids tutorial

--# Main
--Main
 
--This code manages which Code tab is run
--it remembers your last choice, and if you select a different one, it runs that instead
 
local tabs = {}
local fnames = {"setup","draw","touched","collide","orientationChanged","close","restart","keyboard","cleanup"}
local fns = {}   
local tabDesc={}
 
function setup()
    saveProjectInfo("Description", "Step by step tutorial for a simple asteroids game")
    saveProjectInfo("Author", "Graeme West")
    for k,v in ipairs(fnames) do --store addresses of key event functions
        fns[v] = _G[v] 
    end 
    LastCode=readProjectData("Code") or 0  --load stored tab number
    parameter.integer("Choose_a_tab",0,#tabs,LastCode,ShowList) --tab selector
    parameter.action("Run selected tab", RunCode)
    RunCode() 
end
 
function ShowList()
    output.clear()
    for i=0,#tabs do
 --       print(i,tabDesc[i])
    end
end
 
--these two functions do all the tab switching magic (thanks to Andrew_Stacey)
function localise(n,d)
    if d then tabDesc[n]=d end
    local t= {}
    setmetatable(t,{__index = _G})
    setfenv(2,t)
    tabs[n] = t
end
 
--change tabs
function RunCode()
    output.clear()
    saveProjectData("Code",Choose_a_tab)
    cleanup()
    local t = tabs[Choose_a_tab]
    for k,v in ipairs(fnames) do
        if t[v] then _G[v] = t[v] else _G[v] = fns[v] end -- overwrite with the new code
    end
    setup()
end
 
--default empty function to avoid errors for tabs that don't have it
function cleanup()
end
 

--# About
-- Asteroids tutorial
-- by West
 

localise(0,"Intro")
function setup()
    displayMode(STANDARD)
    supportedOrientations(LANDSCAPE_ANY) --locks the screen to use only landscape
end
 
function draw()
    background(40, 40, 50)
    fill(218, 188, 28, 255)
    font("Baskerville-Bold")
    fontSize(32)
    text("Asteroids Tutorial by West",WIDTH/2,HEIGHT-180)
    fontSize(18)
    textWrapWidth(WIDTH-100)
    introtext="This tutorial uses the first few steps of the Snake tutorial "
    introtext = introtext.."to position the space ship on the screen. There are then 6 steps which build up to a simple game of asteroids. "
    introtext = introtext.." These steps are:\n"
    introtext = introtext.."\nStep 1. Get the ship rotating on the screen."
    introtext = introtext.."\nStep 2. Add the firing of laser bullets."
    introtext = introtext.."\nStep 3. Better management of bullets."
    introtext = introtext.."\nStep 4. Add asteroids."
    introtext = introtext.."\nStep 5. Add collision detection."
    introtext = introtext.."\nStep 6. Add different game states, scoring and some polishing."
    
    introtext = introtext.."\n\n Any questions, comments, suggestions post a message on the Codea forums.\n\nGraphics used are those supplied with Codea, particularly those of Kenney.nl and twolivesleft.com"
    text(introtext,WIDTH/2,HEIGHT-400)

    sprite("Cargo Bot:Play Solution Icon",70,HEIGHT-32,-20,20)
    fill(255)
    text("Tap this button to hide/show the sidebar",270,HEIGHT-32)
    
    pushMatrix()
        translate(WIDTH-100,HEIGHT-100)
        rotate(ElapsedTime*25) 
        sprite("Space Art:Red Ship",0,0)
    popMatrix()


end
 

--# Step1
-- Asteroids tutorial
-- by West
 
--Use the first 5 steps of snake as the starter for this tutorial
--1. Control rotation through screen tap - turn the ship towards where the screen was tapped

localise(1,"tab1")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) --locks the screen to use only landscape
    x=512--put ship in centre of screen
    y=HEIGHT/2    
    angle=90 
end
 
function draw()
    background(40, 40, 50)
    
    --this simple example will use the CurrentTouch command. A more advanced (and better) way would be to handle touches separately.  This may be explored later.
    
    -- check to see if the screen has been touched
    if CurrentTouch.state==BEGAN or CurrentTouch.state==MOVING then
        --calculate the angle between the centre of the screen(where the ship is) and the touch point
        angle = math.deg(math.atan2(CurrentTouch.y-y,CurrentTouch.x-x))-90
    end
 
    pushMatrix()
        translate(x,y)
        rotate(angle) 
        sprite("Space Art:Red Ship",0,0,50,40) --change the ship sprite and make smaller
    popMatrix()
end
 

--# Step2
-- Asteroids tutorial
-- by West
 
--2. Add bullets
localise(2,"tab2")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) 
    x=512
    y=HEIGHT/2    
    angle=90 
    bullet={} --a table for the bullet info
    bulletspeed=5
end
 
function draw()
    background(40, 40, 50)
    
    if CurrentTouch.state==BEGAN or CurrentTouch.state==MOVING then
        angle = math.deg(math.atan2(CurrentTouch.y-y,CurrentTouch.x-x))-90
        table.insert(bullet,{x=x,y=y,a=angle})--add a new bullet to the table        
    end
    --a special type of loop for iterating through the table bullet. 
    for i,b in pairs(bullet) do
        --the same code as was used to move the snake sprite in the snake tutorial, except the snake parts are replaced with bullet info (position, angle and sprite)
        pushMatrix()
            translate(b.x,b.y)
            rotate(b.a) 
            sprite("Space Art:Green Bullet",0,0) 
        popMatrix()
        --same maths as was used to kove the snake in the snake tutorial
        b.x = b.x + bulletspeed*math.sin(math.rad(-b.a))
        b.y = b.y + bulletspeed*math.cos(math.rad(-b.a))
    end
 
    pushMatrix()
        translate(x,y)
        rotate(angle) 
        sprite("Space Art:Red Ship",0,0,50,40) 
    popMatrix()
end
 

--# Step3
-- Asteroids tutorial
-- by West
 
--3. Add a delay for the bullets and also remove them when they go off screen 
localise(3,"tab3")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) 
    x=512
    y=HEIGHT/2    
    angle=90 
    bullet={}
    bulletspeed=5
    bulletdelay=10 --a counter for cooling off period between shots
end
 
function draw()
    background(40, 40, 50)
    bulletdelay = bulletdelay -1 --decrease the bullet delay counter
    
    if CurrentTouch.state==BEGAN or CurrentTouch.state==MOVING then
        angle = math.deg(math.atan2(CurrentTouch.y-y,CurrentTouch.x-x))-90
        --only fire the bullet if the delay variable is negative
        if bulletdelay<0 then
            table.insert(bullet,{x=x,y=y,a=angle})--add a new bullet to the table    
            bulletdelay=10 --reset the bullet delay
        end    
    end
 
    for i,b in pairs(bullet) do
        pushMatrix()
            translate(b.x,b.y)
            rotate(b.a) 
            sprite("Space Art:Green Bullet",0,0) 
        popMatrix()
        b.x = b.x + bulletspeed*math.sin(math.rad(-b.a))
        b.y = b.y + bulletspeed*math.cos(math.rad(-b.a))
        --test to see if the bullet has left the screen if so then remove it from the table
        if b.x>WIDTH or b.x<0 or b.y>HEIGHT or b.y<0 then
            table.remove(bullet,i)
        end
    end
 
    pushMatrix()
        translate(x,y)
        rotate(angle) 
        sprite("Space Art:Red Ship",0,0,50,40) 
    popMatrix()
end
 

--# Step4
-- Asteroids tutorial
-- by West
 
--4. Add in asteroids
localise(4,"tab4")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) 
    x=512
    y=HEIGHT/2    
    angle=90 
    bullet={}
    bulletspeed=5
    bulletdelay=10 
    asteroid={} --table to hold asteroid details
    --set up initial asteroid locations
    numAsteroids=2 --initial number of asteroids
    for i=1,numAsteroids do
        table.insert(asteroid,{x=math.random(WIDTH),y=math.random(HEIGHT),angle=math.random(360),size=3,rot=-3+math.random(6),dir=math.random(360),speed=1})
    end
    
end
 
function draw()
    background(40, 40, 50)
    bulletdelay = bulletdelay -1
    
    if CurrentTouch.state==BEGAN or CurrentTouch.state==MOVING then
        angle = math.deg(math.atan2(CurrentTouch.y-y,CurrentTouch.x-x))-90
        if bulletdelay<0 then
            table.insert(bullet,{x=x,y=y,a=angle})
            bulletdelay=10 
        end    
    end
 
    for i,b in pairs(bullet) do
        pushMatrix()
            translate(b.x,b.y)
            rotate(b.a) 
            sprite("Space Art:Green Bullet",0,0) 
        popMatrix()
        b.x = b.x + bulletspeed*math.sin(math.rad(-b.a))
        b.y = b.y + bulletspeed*math.cos(math.rad(-b.a))
        if b.x>WIDTH or b.x<0 or b.y>HEIGHT or b.y<0 then
            table.remove(bullet,i)
        end
    end
 
    for i,a in pairs(asteroid) do
        --same approach as bullet
        pushMatrix()
            translate(a.x,a.y)
            rotate(a.angle) 
            sprite("Space Art:Asteroid Large",0,0,100*a.size/3,100*a.size/3) 
        popMatrix()
        --rotate and move asteroid
        a.angle = a.angle + a.rot
        a.x = a.x + a.speed*math.sin(math.rad(-a.dir))
        a.y = a.y + a.speed*math.cos(math.rad(-a.dir))
        --detect if the asteroid has left the screen, if it has then wrap it round to the other side
        if a.x<0 then 
            a.x=WIDTH
        elseif a.x>WIDTH then
            a.x=0
        end
        if a.y<0 then
            a.y=HEIGHT
        elseif a.y>HEIGHT then
            a.y=0
        end
    end
 
    pushMatrix()
        translate(x,y)
        rotate(angle) 
        sprite("Space Art:Red Ship",0,0,50,40) 
    popMatrix()
end
 

--# Step5
-- Asteroids tutorial
-- by West
 
--5. Add collision detection
localise(5,"tab5")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) 
    x=512
    y=HEIGHT/2    
    angle=90 
    bullet={}
    bulletspeed=5
    bulletdelay=10 
    asteroid={} 
    numAsteroids=2 
    for i=1,numAsteroids do
        table.insert(asteroid,{x=math.random(WIDTH),y=math.random(HEIGHT),angle=math.random(360),size=3,rot=-3+math.random(6),dir=math.random(360),speed=1})
    end
    
end
 
function draw()
    background(40, 40, 50)
    bulletdelay = bulletdelay -1
    
    if CurrentTouch.state==BEGAN or CurrentTouch.state==MOVING then
        angle = math.deg(math.atan2(CurrentTouch.y-y,CurrentTouch.x-x))-90
        if bulletdelay<0 then
            table.insert(bullet,{x=x,y=y,a=angle})
            bulletdelay=10 
        end    
    end
 
    for i,b in pairs(bullet) do
        pushMatrix()
            translate(b.x,b.y)
            rotate(b.a) 
            sprite("Space Art:Green Bullet",0,0) 
        popMatrix()
        b.x = b.x + bulletspeed*math.sin(math.rad(-b.a))
        b.y = b.y + bulletspeed*math.cos(math.rad(-b.a))
        if b.x>WIDTH or b.x<0 or b.y>HEIGHT or b.y<0 then
            table.remove(bullet,i)
        end
    end
 
    for i,a in pairs(asteroid) do
        pushMatrix()
            translate(a.x,a.y)
            rotate(a.angle) 
            sprite("Space Art:Asteroid Large",0,0,100*a.size/3,100*a.size/3) 
        popMatrix()
        a.angle = a.angle + a.rot
        a.x = a.x + a.speed*math.sin(math.rad(-a.dir))
        a.y = a.y + a.speed*math.cos(math.rad(-a.dir))
        if a.x<0 then 
            a.x=WIDTH
        elseif a.x>WIDTH then
            a.x=0
        end
        if a.y<0 then
            a.y=HEIGHT
        elseif a.y>HEIGHT then
            a.y=0
        end
        --for each asteroid check all the bullets to see if there is a collision
        for j,b in pairs(bullet) do
            if math.abs(a.x-b.x)<50*a.size/3 and math.abs(a.y-b.y)<50*a.size/3 then
                --if there is a collision then remove the bullet
                table.remove(bullet,j)
                --if the asteroid is bigger than the smallest one the split into two smaller asteroids travelling in different directions
                if a.size>1 then
                    table.insert(asteroid,{x=a.x,y=a.y,angle=a.angle+90,size=a.size-1,rot=-3+math.random(6),dir=a.dir+90,speed=a.speed+1})
                    table.insert(asteroid,{x=a.x,y=a.y,angle=a.angle-90,size=a.size-1,rot=-3+math.random(6),dir=a.dir-90,speed=a.speed+1})
                end
                table.remove(asteroid,i)
            end
        end
        --now check to see if the asteroid has hit the ship
        if math.abs(a.x-x)<50*a.size/3 and math.abs(a.y-y)<50*a.size/3 then
            --flash
            background(math.random(255),math.random(255),math.random(255))
            table.remove(asteroid,i)
        end
    end
    
    --Do a check to see if any asteroids are left, if not print a winning message
    if #asteroid<1 then
        fontSize(32)
        text("You Win!",WIDTH/2,HEIGHT*2/3)
    end
    pushMatrix()
        translate(x,y)
        rotate(angle) 
        sprite("Space Art:Red Ship",0,0,50,40) 
    popMatrix()
end
 

--# Step6
-- Asteroids tutorial
-- by West
 
--6. Add finite state machine,scoring and general polishing
localise(6,"tab6")
function setup()
    displayMode(FULLSCREEN)
    supportedOrientations(LANDSCAPE_ANY) 
    --Define the possible game states
    READY=1
    PLAYING=2
    LEVELCOMPLETE=3
    LOSE=4
    gamestate=READY
    --sounds - there is a small delay when a sound is played for the first time. Play them in the set up with zero volume to avoid a jitter during the game. I preview using the sound command here to get the id, then set this as a variable
    --sound(SOUND_SHOOT, 23109)
    shootsound=23109
    --now play with zero volume
    sound(SOUND_SHOOT,shootsound,0)
    --repeat for the explosions, but store in a table. the position in the table will match the size of the asteroid
    expsound={36012,36018,36002}
--    sound(SOUND_EXPLODE, 36018)
    for i=1,#expsound do
        sound(SOUND_EXPLODE, expsound[i],0)
    end
    --and gameover sound
    deadexp=47415
    --and level complete sound
    sound(SOUND_EXPLODE,deadexp,0)
    levelup=47367
    sound(SOUND_RANDOM,levelup,0)
    x=512
    y=HEIGHT/2    
    angle=90 
    bullet={}
    bulletspeed=10 --make the bullets faster...
    bulletdelay=35 --..but less often
    asteroid={} 
    numAsteroids=2 
    score=0
    touches={}
    --add in some variables to monitor a delay between screens
    counter=200
    delay=100
    --add in spacedust
    spacedust={}
end
 
function initialiseAsteroids()
    for i=1,numAsteroids do
        local ax=math.random(WIDTH)
        local ay=math.random(HEIGHT)
        --check to see if this puts the asteroid on the ship which would mean instant death.  if this is the case then move it by 300 to the side
        if math.abs(ax-WIDTH/2)<100 and math.abs(ay-HEIGHT/2)<100 then
            ax = ax + 300
        end
        table.insert(asteroid,{x=ax,y=ay,angle=math.random(360),size=3,rot=-3+math.random(6),dir=math.random(360),speed=1})
    end
    counter=0
end
 
function draw() 
    background(0) --the space dust fades to black so the background should reflect this
    --Add in the main menu screen
    if gamestate==READY then
        counter = counter + 1
        font("ArialRoundedMTBold")
        fontSize(64)
        --Only show the title at the start
        if numAsteroids==2 then
            text("Asteroid Field",WIDTH/2,HEIGHT-200)
            fontSize(32)
            text("by West",WIDTH/2,HEIGHT-250)
            fontSize(64)
        end
        text("Level "..(numAsteroids-1),WIDTH/2,HEIGHT/2)
        fontSize(18)
        text("Remember, the odds of successfully navigating an asteroid field are approximately 3,720 to 1",WIDTH/2,150)
        if counter>delay then
            fontSize(64)
            text("Ready?",WIDTH/2,HEIGHT/2-100)
        end
        --loop through the touch table - if any touches appear move to the next game state, provided the counter is past the time limit
        for k,touch in pairs(touches) do       
            --any touch will do
            if counter>delay then
                initialiseAsteroids()
                gamestate=PLAYING
            end
        end
    --the main game routine
    elseif gamestate==PLAYING then
            bulletdelay = bulletdelay -1
            for k,touch in pairs(touches) do        
                angle = math.deg(math.atan2(touch.y-y,touch.x-x))-90
                if bulletdelay<0 then
                    table.insert(bullet,{x=x,y=y,a=angle})
                    bulletdelay=10 
                    sound(SOUND_SHOOT,shootsound)
                end            
            end
            for i,b in pairs(bullet) do
                pushMatrix()
                    translate(b.x,b.y)
                    rotate(b.a) 
                    sprite("Space Art:Green Bullet",0,0) 
                popMatrix()
                b.x = b.x + bulletspeed*math.sin(math.rad(-b.a))
                b.y = b.y + bulletspeed*math.cos(math.rad(-b.a))
                if b.x>WIDTH or b.x<0 or b.y>HEIGHT or b.y<0 then
                    table.remove(bullet,i)
                end
            end
        
            for i,a in pairs(asteroid) do
                pushMatrix()
                    translate(a.x,a.y)
                    rotate(a.angle) 
                    sprite("Space Art:Asteroid Large",0,0,100*a.size/3,100*a.size/3) 
                popMatrix()
                a.angle = a.angle + a.rot
                a.x = a.x + a.speed*math.sin(math.rad(-a.dir))
                a.y = a.y + a.speed*math.cos(math.rad(-a.dir))
                if a.x<0 then 
                    a.x=WIDTH
                elseif a.x>WIDTH then
                    a.x=0
                end
                if a.y<0 then
                    a.y=HEIGHT
                elseif a.y>HEIGHT then
                    a.y=0
                end
                for j,b in pairs(bullet) do
                    if math.abs(a.x-b.x)<50*a.size/3 and math.abs(a.y-b.y)<50*a.size/3 then
                        table.remove(bullet,j)
                        --increase the score 10 points for big asteroid, 15 for a medium and 30 for a small
                        score=score+30/a.size
                        --play explosion sound
                        sound(SOUND_EXPLODE, expsound[a.size])
                        if a.size>1 then
                            table.insert(asteroid,{x=a.x,y=a.y,angle=a.angle+90,size=a.size-1,rot=-3+math.random(6),dir=a.dir+90,speed=a.speed+1})
                            table.insert(asteroid,{x=a.x,y=a.y,angle=a.angle-90,size=a.size-1,rot=-3+math.random(6),dir=a.dir-90,speed=a.speed+1})
                        end
                        table.remove(asteroid,i)
                        --add spacedust, variable s will be the angle
                        for s=0,360,12 do                            
                            table.insert(spacedust,{x=a.x,y=a.y,dir=s,fade=175+math.random(50)+3*a.size,size=2*a.size+math.random(5),speed=5+math.random(5)})
                        end
                    end
                end
                if math.abs(a.x-x)<50*a.size/3 and math.abs(a.y-y)<50*a.size/3 then
                    background(math.random(255),math.random(255),math.random(255))
                    table.remove(asteroid,i)
                    gamestate=LOSE
                    counter=0
                end
            end
            --if there are no asteroids left and that the last one wasn't destroyed by hitting the ship then the level is complete
            if #asteroid<1 and gamestate~=LOSE then
                    gamestate=LEVELCOMPLETE
            end
            pushMatrix()
                translate(x,y)
                rotate(angle) 
                sprite("Space Art:Red Ship",0,0,50,40) 
            popMatrix()
            
            --draw the spacedust - this is similar to the asteroid routine
            for s,d in pairs(spacedust) do
            --add transparency to the space dust so it fadees away
            tint(d.fade)
            pushMatrix()
                translate(d.x,d.y)
                sprite("Cargo Bot:Star Filled",0,0,d.size,d.size) 
            popMatrix()
                d.x = d.x + d.speed*math.sin(math.rad(-d.dir))
                d.y = d.y + d.speed*math.cos(math.rad(-d.dir))
                d.fade = d.fade -5
                if d.fade<0 then
                    table.remove(spacedust,s)
                end
            end
            tint(255)
            fontSize(18)
            text("Score: "..score,100,HEIGHT-50)
    --level complete    
    elseif gamestate==LEVELCOMPLETE then
        if counter==3 then
            sound(SOUND_RANDOM,levelup)
        end
        counter = counter + 1
        font("ArialRoundedMTBold")
        fontSize(64)
        text("Level "..(numAsteroids-1).." complete",WIDTH/2,HEIGHT/2)
        if counter>delay then
            text("Next level?",WIDTH/2,HEIGHT/2-100)
        end
        for k,touch in pairs(touches) do       
            --any touch will do
            if counter>delay then
                --increase the number of asteroids (the level is always 1 less than the number of asteroids)
                numAsteroids = numAsteroids + 1
                counter=0
                gamestate=READY
            end
        end
    --Game over, man. Game over.
    elseif gamestate==LOSE then
        if counter==3 then
            sound(SOUND_EXPLODE,deadexp)
        end
        counter = counter + 1
        font("ArialRoundedMTBold")
        fontSize(32)
        text("Game over man, Game over. Your final score is "..score,WIDTH/2,HEIGHT/2)
        if counter>delay then
            text("Try again?",WIDTH/2,HEIGHT/2-100)
        end
        for k,touch in pairs(touches) do       
            --any touch will do
            if counter>delay then
                --reset the level/number of asteroids
                numAsteroids = 2
                counter=0
                --reset the score
                score=0
                gamestate=READY
            end
        end
    end
end
 
function touched(touch)
    if touch.state == ENDED then
        touches[touch.id] = nil
    else
        touches[touch.id] = touch       
    end
end