Corona SDK adding physics bodies/ not accepting collisions

Question

I am attempting to add/remove objects from the physics engine (addBody() and removeBody()) in an app I am working on. The app I am working on is modular so the issue is in one of two files.

The objects file (TransmitterObject) or the main file (main):

This is the relevant code for both:

main.lua

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


local TransmitterObject = require("TransmitterObject")

function updateGame(event)

    if(ITERATIONS % 100 == 0) then
        tran1:activate()    --create new physics object here    
    end

    ITERATIONS = ITERATIONS + 1
    --print(ITERATIONS)
end

Runtime:addEventListener("enterFrame", updateGame)

TransmitterObject.lua

function transmitter.new(props) --constructor
    Transmitter = 
    {
        x = props.x,
        y = props.y,
        receivers = props.receivers
    }

    return setmetatable( Transmitter, transmitter_mt )      
end

function transmitter:activate() 
    local group = math.random(1, #self.receivers)
    local receiver = math.random(1,#self.receivers[group])
    local x , y = self.receivers[group][receiver][1], self.receivers[group][receiver][2]
    local d = math.sqrt(math.pow((self.x-x),2) + math.pow((self.y-y),2))
    local dx = math.abs(self.x - x)
    local angle = math.deg(math.acos(dx/d))


    local beam = display.newRect(self.x,self.y, d, 10)
    beam:setReferencePoint(display.TopLeftReferencePoint)
    beam.rotation = 180 + angle
    beam:setFillColor(0,255,0)
    beam.alpha = 0

    local function add(event)
        physics.addBody(beam, "static")
    end

    local function delete(event)
        physics.removeBody(beam)
    end 

    transition.to( beam, { time=1000, alpha=1.0, onComplete=add } )
    transition.to( beam, { time=1000, delay=2500, alpha=0, onComplete=delete})  
end

Now let me try to describe the issue a little better. basically every 100th time that 'enterFrame' fires I tell the transmitter object (tran1) to call its function 'activate' which then preforms some basic math to get coordinates. Then it creates a rectangle (beam) using the calculated information and sets some properties. That is all basic stuff. Next I tell it to transition from not visible (alpha = 0) to visible over the span of 1 second. When does it is to call the function 'add' which adds the object to the physics engine. Likewise with the next line where it removes the objects.

That being said, when i set physics.setDrawMode( "debug" ) the beam object appears as a static body, but does not accept collisions. Does anyone know why the above code would not accept collisions for the beam object?

Keep in mind I have other objects that do work properly within the physics engine.

Fannick Fannick · Accepted Answer · 2014-01-24T15:03:06

Wow, I'm answering super late!
On collisions, modifying bodies aren't supported.
What I propose you is to create a new function,

local function addBody ( event )
physics.addBody(ball, "static")
end

and in your collision event you have to add this,

timer.performWithDelay(500, addBody)

The only thing that may cause some problems it's the delay, but as the collision doesn't take too much time it should be ok.
Sorry for this necroposting,
It's just to help other people that may have that problem,
Fannick

Corona SDK adding physics bodies/ not accepting collisions

1 Answers