Help with Collision of spawned object(postion fixed) with objects that there are translating on screen

Question

Hey guys I am creating a game using Corona SDK and so coding it in Lua. So there are 2 separate functions,

1. To translate the hit objects and change their color when they are tapped The link below is the code I am using to for the first function http://developer.anscamobile.com/sample-code/fishies

2. Spawn objects that will hit the translating objects on collision. Alos on collision the spawned object disappears and the translating object bears a color(indicating the collision). In addition the size of this spawned object is dependent on i/p volume level. The function I have written is as follows:

   --VOICE INPUT CODE
   local r = media.newRecording()
   r:startRecording()
   r:startTuner()
   
   --local function newBar()
   --    local bar = display.newLine( 0, 0, 1, 0 ) 
   --    bar:setColor( 0, 55, 100, 20 )
   --    bar.width = 5
   --    bar.y=400
   --    bar.x=20
   --    return bar
   --end
   
   local c1 = display.newImage("str-minion-small.png")
   c1.isVisible=false
   local c2 = display.newImage("str-minion-mid.png")
   c2.isVisible=false
   local c3 = display.newImage("str-minion-big.png")
   c3.isVisible=false
   
   --SPAWNING
   local function spawnDisk( event )
       local phase = event.phase
   
       local volumeBar = display.newLine( 0, 0, 1, 0 )
       volumeBar.y =  400
       volumeBar.x = 20
       --volumeBar.isVisible=false
   
       local v = 20*math.log(r:getTunerVolume())    
       local MINTHRESH = 30
       local LEFTMARGIN = 20
       local v2 = MINTHRESH + math.max (v, -MINTHRESH)
       v2 = (display.contentWidth - 1 * LEFTMARGIN ) * v2 / MINTHRESH
       volumeBar.xScale =  math.max ( 20, v2 )
   
       local l = volumeBar.xScale
       local cnt1 = 0
       local cnt2 = 0
       local cnt3 = 0
       local ONE =1
       local val = event.numTaps
       --local px=event.x
       --local py=event.y
   
       if "ended" == phase then
           --audio.play( popSound )
           --myLabel.isVisible = false
   
           if l > 50 and l <=150 then
               --c1:setFillColor(10,105,0)
               --c1.isVisible=false
               c1.x=math.random( 10, 450 )
               c1.y=math.random( 10, 300 )
               physics.addBody( c1, { density=1, radius=10.0 } )
               c1.isVisible=true
               cnt1= cnt1+ ONE
               return c1
   
           elseif l > 100 and l <=250 then
               --c2:setFillColor(200,10,0)
               c2.x=math.random( 10, 450 )
               c2.y=math.random( 10, 300 )
               physics.addBody( c2, { density=2, radius=9000.0 } )
               c2.isVisible=true
               cnt2= cnt2+ ONE
               return c2
   
           elseif l >=250 then
               c3.x=math.random( 40, 450 )
               c3.y=math.random( 40, 300 )
               physics.addBody( c3, { density=2, radius=7000.0 , bounce=0.0 } )
               c3.isVisible=true
               cnt3= cnt3+ ONE
               return c3
           end
       end
   end
   
   buzzR:addEventListener( "touch", spawnDisk ) -- touch the screen to create disks
   

Now both functions work fine independently but there is no collision happening. Its almost as if the translating object and the spawn object are on different layers. The translating object passes through the spawn object freely.

Can anyone please tell me how to resolve this problem. And how can I get them to collide.

Its my first attempt at game development, that too for a mobile platform so would appreciate all help. Also if I have not been specific do let me know. I'll try to frame the query better :).

Thanks in advance.

Answer 1

I think the problem is that the objects are all inserted into a group in the Fishies code. That is, your comment that they seem to be on different layers is correct. Note line 113:

group:insert( fishOriginal, true )

Physics don't work between display groups. This was done on purpose so that you can move the group around without affecting anything in the group, in order to do a moving camera like the Egg Breaker demo.