Some nooby questions

Questions
1

Hi, as my first game using Lua I am making a game where you are a rocket, and you try to dodge asteroids. I have a few questions.

  1. I’ve written a program for the asteroid movement and speed, but I am wondering how to make it work for multiple asteroids at once. I’m using various variables, but other than duplicating it and renaming all the variables how can I make it work for multiple sprites at once?

  2. I am having trouble making the program detect whether the rocket is touching the asteroid. Is there a basic way of doing this?

  3. My brother is also having a go at Codea, and he wants to make buttons that move his character right and left. I’ve tried to work it out myself, but I’m quite confused about how.

So yeah. Apologies for our noobiness. Any help would be greatly appreciated (by both me and my brother) as we would love to be able to program apps ourselves :slight_smile:

2

@Purplecreature - simple one first, search the for buttons. Set up two simple buttons - you can use the UI sprites in the resources library. Use touch to detect when each button is touched then move the sprite by changing the x and y values in the sprite command:


sprite(button_left, xposition, yposition, sprite width, spriteheight)

If you search the forum, and the Wiki, you will be able to find many examples of using touch. Try @ignatz website (link in the Wiki) which covers many of the Codea features that you will need for this.

Question on the rocket - is this a 2D program - rocket and asteroid move in x and y coordinates onscreen? Or, is it 3D where the asteroids are flying towards you - very different approach.= to these.

On making multiple asteroids you need to set up an asteroid Class which contains the data needed to generate the asteroid - e.g. the x and y position and size of each asteroid. Then you an provide a loop to interogate each asteroid and move it (in small increments) in whatever direction you choose or a random one.

Hint - collision detection involves measuring the distance between the each asteroid and the rocket - compensation if needed for the size of rocket and asteroid.

I’ll look for an example in the forum - hope that helps to get you started.

Edit: try looking at the following link - a simple asteroids game

https://pastebin.com/uTcXchab

3

@Purplecreature Here’s a simple example I threw together to give you an idea of things to try. Move your finger anywhere on the screen to move the ship up/down/right/left. Avoid the asteroids. Each asteroid that goes off the screen bottom increments the count at the top. Each asteroid hit decrements the ship count at the upper left. When over, press the restart icon to play again. Hold the iPad in portrait mode. You can add sound or other things to expand what’s happening. If you have questions, just ask.

displayMode(FULLSCREEN)

function setup()
    fontSize(40)
    asteroids=30
    past=0
    ships=5
    dx,dy=WIDTH/2,200
    ast={}
    for z=1,asteroids do
        addAsteroid()
    end           
end

function draw()
    background(0, 203, 255, 255)    
    fill(255,0,0)
    text(past,WIDTH/2,HEIGHT-50)
    if ships==0 then
        text("Press restart icon to play again.",WIDTH/2,HEIGHT/2)
        return
    end
    for z=1,#ast do
        sprite("Space Art:Asteroid Small",ast[z].x,ast[z].y)
        ast[z].y=ast[z].y-ast[z].z
    end
    chkPosition()
    sprite("Tyrian Remastered:Plane Boss",dx,dy,-100)  
    chkCollision() 
    for z=1,ships do
        sprite("Tyrian Remastered:Plane Boss",40*z,HEIGHT-30,30)
    end
end

function chkPosition()
    for z=#ast,1,-1 do
        if ast[z].y<-50 then
            table.remove(ast,z)
            past=past+1
            addAsteroid()
        end        
    end
end

function addAsteroid()
    table.insert(ast,vec3(math.random(10,WIDTH-10),
        math.random(HEIGHT+30,HEIGHT+500),math.random(2,5)))            
end

function chkCollision()
    for z=#ast,1,-1 do
        v1=vec2(dx,dy)
        d=v1:dist(vec2(ast[z].x,ast[z].y))
        if d<65 then
            table.remove(ast,z)
            ships=ships-1
            addAsteroid()
        end
    end
end

function touched(t)
    if t.state==MOVING then
        dx=dx+t.deltaX
        dy=dy+t.deltaY
    end
end
4

@Bri_G @dave1707 Thanks so much! I’ve used both codes and now my game is functional!

Just two more things - Firstly, I’m probably just being really dumb, but how exactly do you make a button with touch commands? And secondly, is there an easy way to make the game stop when you die?

5

@Purplecreature - the button is actually a sprite - any sprite. The UI resources includes many with Codea. The trick is to check in the area where the button is, that’s x and y coordinates to ensure you have touched the screen there, either when a touch has been initiated (BEGAN) or stopped (ENDED). The MOVING option is generally for dragging sprites.

Try :


if lives > 0 then
    play()
else
    demo()
end
6

@Purplecreature Here’s a simple 2 button example. Tap the left of right button to move the sprite left or right. Or just slide your finger from button to button. Normally a class would be used to create buttons, but since I don’t know if you know how to use classes, I just did this.

displayMode(FULLSCREEN)

function setup()
    rectMode(CENTER)
    b1=vec4(WIDTH/2-50,200,100,50)
    b2=vec4(WIDTH/2+50,200,100,50)
    sx,sy=WIDTH/2,HEIGHT/2  -- sprite x,y
    xs=0    -- x speed
end

function draw()
    background(0)
    fill(255)
    rect(b1.x,b1.y,b1.z,b1.w)   -- button 1
    rect(b2.x,b2.y,b2.z,b2.w)   -- button 2
    fill(255,0,0)
    text("Left",b1.x,b1.y)
    text("Right",b2.x,b2.y)
    sprite("Planet Cute:Star",sx,sy)
    sx=sx+xs
end

function touched(t)
    if t.state==BEGAN or t.state==MOVING then
        xs=0
        if t.x>b1.x-b1.z/2 and t.x<b1.x+b1.z/2 and
            t.y>b1.y-b1.w/2 and t.y<b1.y+b1.z/2 then
                xs=-1
        end
        if t.x>b2.x-b2.z/2 and t.x<b2.x+b2.z/2 and
            t.y>b2.y-b2.w/2 and t.y<b2.y+b1.z/2 then
                xs=1
        end
    elseif t.state==ENDED then
        xs=0
    end
end
7

@Purplecreature Here’s an example that uses a button class just in case you’re interested. I added up/down buttons.

displayMode(FULLSCREEN)

function setup()
    rectMode(CENTER)
    bTab={}
    table.insert(bTab,button(WIDTH/2-70,150,100,50,-1,0,"Left"))
    table.insert(bTab,button(WIDTH/2+70,150,100,50,1,0,"Right"))
    table.insert(bTab,button(WIDTH/2,200,100,50,0,1,"Up"))
    table.insert(bTab,button(WIDTH/2,100,100,50,0,-1,"Down"))
    sx,sy=WIDTH/2,HEIGHT/2  -- sprite x,y
end

function draw()
    background(0)
    sprite("Planet Cute:Star",sx,sy)
    for a,b in pairs(bTab) do
        b:draw()
    end
    sx=sx+button.xs
    sy=sy+button.ys
end

function touched(t)
    button.xs,button.ys=0,0
    for a,b in pairs(bTab) do
        b:touched(t)
    end
end

button=class()

button.xs=0
button.ys=0

function button:init(x,y,w,h,xs,ys,txt)
    self.x=x
    self.y=y
    self.w=w
    self.h=h 
    self.xs=xs
    self.ys=ys 
    self.text=txt
end

function button:draw()
    fill(255)
    rect(self.x,self.y,self.w,self.h)
    fill(255,0,0)
    text(self.text,self.x,self.y)
end

function button:touched(t)
    if t.state==BEGAN or t.state==MOVING then
        if t.x>self.x-self.w/2 and t.x<self.x+self.w/2 and
                t.y>self.y-self.h/2 and t.y<self.y+self.h/2 then            
            button.xs,button.ys=self.xs,self.ys
        end
    end
end
8

@dave1707 @Bri_G Thanks again! Very useful!