Little problems

General
1

Hi all!

I’m messing with a little program, trying to get pairs of ellipses to spawn every second randomly at 2 of 4 designated locations.

I have 3 problems though…

First, the ellipses stop spawning after spawning 1-3 times.

Second, for some reason some of the ellipses increase in speed as they get to the bottom of the screen, they should be moving at a constant velocity.

Third, I can’t figure out how to get the ellipses to not spawn 2 ellipses at the same location…

Any tips on how to fix any of these problems would be greatly appreciated!

Here is what the code looks like:


supportedOrientations(PORTRAIT_ANY)
displayMode(FULLSCREEN)

-- Use this function to perform your initial setup
function setup()
    balls={}
    ball=readImage("Space Art:Asteroid Small")
    spawnLoc={vec2(WIDTH/2.7,1152),vec2(WIDTH/7.8,1152),
    vec2(WIDTH/1.6,1152),vec2(WIDTH/1.16,1152)}
    ballSpeed=-15
    counter=0
    ballFreq=60
end

function ballSpawn()
    local random = math.random(1,4)
    table.insert(balls,spawnLoc[random])
end
-- This function gets called once every frame
function draw()
    
    background(0,0,0,255)
    
    counter=counter+1
    
    fill(255, 0, 0, 255)
    
    for a,b in ipairs(balls) do
        ellipse(b.x,b.y,128,128)
        b.y=b.y+ballSpeed
    end
    
    if counter%ballFreq==0 then
        ballSpawn()
        ballSpawn()
    end
    
end
2

@Crumble - Try this, no time to explain, will do so in a little while


supportedOrientations(PORTRAIT_ANY)
displayMode(FULLSCREEN)

-- Use this function to perform your initial setup
function setup()
    balls={}
    ball=readImage("Space Art:Asteroid Small")
    spawnLoc={vec2(WIDTH/2.7,1152),vec2(WIDTH/7.8,1152),
    vec2(WIDTH/1.6,1152),vec2(WIDTH/1.16,1152)}
    ballSpeed=-15*60
    counter=0
    ballFreq=60
end

function ballSpawn(n)
    local t={1,2,3,4}
    for i=1,n do
        local random = math.random(1,#t)
        table.insert(balls,vec2(spawnLoc[t[random]].x,spawnLoc[t[random]].y))
        table.remove(t,random)
    end
end
-- This function gets called once every frame
function draw()

    background(0,0,0,255)

    counter=counter+1

    fill(255, 0, 0, 255)

    for a,b in ipairs(balls) do
        ellipse(b.x,b.y,128,128)
        b.y=b.y+ballSpeed*DeltaTime
        if b.y<0 then b=nil end
    end

    if counter%ballFreq==0 then
        ballSpawn(2)
    end

end
3

ok, I fixed the balls so they don’t start in the same place

the reason the balls speeded up and also why they stopped appearing is explained in this post

http://coolcodea.wordpress.com/2013/06/14/84-tables-and-pointers/

While that post is about tables, the same applies to vec2

So

a=vec2(1,1)
b=a
c=vec2(a.x,a.y)
b.x=3
print(a) -- (3,1)
print(b) -- (3,1)
print(c) -- (1,1)

In this example, b is not given a copy of a, but is given the address of a, so it is pointing at the same vec2. This means any change to b also affects a.

On the other hand, c is created by coping the individual x and y values of a, and because these are just numbers, Codea does make separate copies of them.

4

Awesome, that works perfect. Now to wrap my head around what is going on in the ballSpawn function.

Thanks for the help!