main.lua

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--
-- main.lua
--
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-- Your code here

local physics = require("physics")
physics.start()
physics.setGravity(0,0)

math.randomseed(os.time())
local sheetOptions = 
{
    frames = 
    {
        {   -- 1) asteroid 1
            x = 0,
            y = 0,
            width = 102,
            height = 85
        },
        {   -- 2) asteroid 2
            x = 0,
            y = 85,
            width = 90,
            height = 83
        },
        {   -- 3) asteroid 3
            x = 0,
            y = 168,
            width = 100,
            height = 97
        },
        {   -- 4) ship
            x = 0,
            y = 265,
            width = 98,
            height = 79
        },
        {   -- 5) laser
            x = 98,
            y = 265,
            width = 14,
            height = 40
        },
    },
}

local objectSheet = graphics.newImageSheet("gameObjects.png",sheetOptions)

-- Initialize variables
local lives = 3
local score = 0
local died = false
 
local asteroidsTable = {}
 
local ship
local gameLoopTimer
local livesText
local scoreText

-- Set up display groups
local backGroup = display.newGroup()  -- Display group for the background image
local mainGroup = display.newGroup()  -- Display group for the ship, asteroids, lasers, etc.
local uiGroup = display.newGroup()    -- Display group for UI objects like the score

-- Load the background
local background = display.newImageRect( backGroup, "background.png", 800, 1400 )
background.x = display.contentCenterX
background.y = display.contentCenterY

ship = display.newImageRect( mainGroup, objectSheet, 4, 98, 79 )
ship.x = display.contentCenterX
ship.y = display.contentHeight - 100
physics.addBody( ship, { radius=30, isSensor=true } )
ship.myName = "ship"

-- Display lives and score
livesText = display.newText( uiGroup, "Lives: " .. lives, 200, 80, native.systemFont, 36 )
scoreText = display.newText( uiGroup, "Score: " .. score, 400, 80, native.systemFont, 36 )

display.setStatusBar( display.HiddenStatusBar )

local function updateText()
    livesText.text = "Lives: " .. lives
    scoreText.text = "Score: " .. score
end

local function createAsteroid()
 
    local newAsteroid = display.newImageRect( mainGroup, objectSheet, 1, 102, 85 )
    table.insert( asteroidsTable, newAsteroid )
    physics.addBody( newAsteroid, "dynamic", { radius=40, bounce=0.8 } )
    newAsteroid.myName = "asteroid"

    local whereFrom = math.random( 3 )
 
    if ( whereFrom == 1 ) then
        -- From the left
        newAsteroid.x = -60
        newAsteroid.y = math.random( 500 )
        newAsteroid:setLinearVelocity( math.random( 40,120 ), math.random( 20,60 ) )
    elseif ( whereFrom == 2 ) then
        -- From the top
        newAsteroid.x = math.random( display.contentWidth )
        newAsteroid.y = -60
        newAsteroid:setLinearVelocity( math.random( -40,40 ), math.random( 40,120 ) )
    elseif ( whereFrom == 3 ) then
        -- From the right
        newAsteroid.x = display.contentWidth + 60
        newAsteroid.y = math.random( 500 )
        newAsteroid:setLinearVelocity( math.random( -120,-40 ), math.random( 20,60 ) )
    end

    newAsteroid:applyTorque( math.random( -6,6 ) )
end

local function fireLaser()
 
    local newLaser = display.newImageRect( mainGroup, objectSheet, 5, 14, 40 )
    physics.addBody( newLaser, "dynamic", { isSensor=true } )
    newLaser.isBullet = true
    newLaser.myName = "laser"

    newLaser.x = ship.x
    newLaser.y = ship.y

    newLaser:toBack()

    transition.to( newLaser, { y=-40, time=500, 
        onComplete = function() display.remove( newLaser ) end
    } )

end

ship:addEventListener( "tap", fireLaser )


local function dragShip( event )
 
    local ship = event.target
    local phase = event.phase
 
    if ( "began" == phase ) then
        -- Set touch focus on the ship
        display.currentStage:setFocus( ship )
        -- Store initial offset position
        ship.touchOffsetX = event.x - ship.x
 
    elseif ( "moved" == phase ) then
        -- Move the ship to the new touch position
        ship.x = event.x - ship.touchOffsetX
    elseif ( "ended" == phase or "cancelled" == phase ) then
        -- Release touch focus on the ship
        display.currentStage:setFocus( nil )
    end
    return true  -- Prevents touch propagation to underlying objects
end
ship:addEventListener( "touch", dragShip )

local function gameLoop()
 
    -- Create new asteroid
    createAsteroid()
 
    -- Remove asteroids which have drifted off screen
    for i = #asteroidsTable, 1, -1 do
        local thisAsteroid = asteroidsTable[i]
 
        if ( thisAsteroid.x < -100 or
             thisAsteroid.x > display.contentWidth + 100 or
             thisAsteroid.y < -100 or
             thisAsteroid.y > display.contentHeight + 100 )
        then
            display.remove( thisAsteroid )
            table.remove( asteroidsTable, i )
        end
    end
end
gameLoopTimer = timer.performWithDelay( 500, gameLoop, 0 )

local function restoreShip()
 
    ship.isBodyActive = false
    ship.x = display.contentCenterX
    ship.y = display.contentHeight - 100
 
    -- Fade in the ship
    transition.to( ship, { alpha=1, time=4000,
        onComplete = function()
            ship.isBodyActive = true
            died = false
        end
    } )
end

local function namePair(obj1, obj2, name1, name2)
    return ( obj1.myName == name1 and obj2.myName == name2 ) or
    ( obj1.myName == name2 and obj2.myName == name1 )
end

local function onCollision( event )
 
    if ( event.phase == "began" ) then
        local obj1 = event.object1
        local obj2 = event.object2
     
        if (namePair(obj1,obj2,"laser","asteroid")) then
           -- Remove both the laser and asteroid
           display.remove( obj1 )
           display.remove( obj2 )
           for i = #asteroidsTable, 1, -1 do
                if ( asteroidsTable[i] == obj1 or asteroidsTable[i] == obj2 ) then
                    table.remove( asteroidsTable, i )
                    break
                end
            end
        
            -- Increase score
            score = score + 100
            scoreText.text = "Score: " .. score       
     
        elseif (namePair(obj1,obj2,"ship","asteroid")) then
            if ( died == false ) then
                died = true

                -- Update lives
                lives = lives - 1
                livesText.text = "Lives: " .. lives
               
                if ( lives == 0 ) then
                    display.remove( ship )
                else
                    ship.alpha = 0
                    timer.performWithDelay( 1000, restoreShip )
                end
 
            end
        end
    end
end

Runtime:addEventListener( "collision", onCollision )