radial gravity problem

[harryjnewton]

hey everybody

i have recently just started using the radial gravity code from the tutorial and i have started having some problems

first of all, basically when an object enters the field it want it to be attracted by the gravity which is what it is doing but you can only apply the radial gravity to one field using the

 setTarget(  )  

and when i try using two of these in the same function it glitches out were as it when an object hit a filed (any two of them, it only attracts to one. so then i tried using 

setTarget(self.x,self.y  )  

and when the object just entered the field it was only attracted to the edges of the field, not the center.

How do i fix this major problem? 

here is my code. I only took the relevant parts of the code.

Thanks, Hazza

                            

[lua]

---

                            –

                            – main.lua

                            –

                            -----------------------------------------------------------------------------------------

                            

                            – Your code here

                            

                            – Physics Demo: Radial Gravity | Version: 1.0

                            – Sample code is MIT licensed, see http://www.coronalabs.com/links/code/license

                            – Copyright © 2013 Corona Labs Inc. All Rights Reserved.

local physics = require(“physics”) ; physics.start() ; physics.setGravity( 0,0 ) ; physics.setDrawMode( “hybrid” )

display.setStatusBar( display.HiddenStatusBar )

math.randomseed( os.time() )

local ox, oy = math.abs(display.screenOriginX), math.abs(display.screenOriginY)

local cw, ch = display.contentWidth, display.contentHeight

                            

                            --set up collision filters

local screenFilter = { categoryBits=2, maskBits=1 }

local objFilter = { categoryBits=1, maskBits=14 }

local fieldFilter = { categoryBits=4, maskBits=1 }

local magnetFilter = { categoryBits=8, maskBits=1 }

                            

                            

                            

                            

                            --set initial magnet pull

local magnetPull = 0.25

local centerX = display.contentWidth*.5

local centerY = display.contentHeight * .5

local obj

local projFiring

local magnet2

local displayScore

local scoreObj

local score = 0

local displayAmmo

local ammoObj

local Ammo = 6

local field

local magnet

local secondField

                            --set up world and background

                            

                            

                    

                            

local function setupWorld()

                            

local back = display.newImage( “background.png” ) ; back.x = cw/2 ; back.y = ch/2 ;

local screenBounds = display.newRect( -ox, -oy, display.contentWidth+ox+ox, display.contentHeight+oy+oy )

screenBounds.name = “screenBounds”

screenBounds.isVisible = false ; physics.addBody( screenBounds, “static”, { isSensor=true, filter=screenFilter } )

                            

field = display.newImageRect( “field.png”, 180,180 ) ; field.alpha = 0.3

field.name = “field”

field.x = display.contentCenterX - 60 ; field.y = display.contentCenterY - 60

physics.addBody( field, “static”, { isSensor=true, radius=90, filter=fieldFilter } )

–field.touchJoint:setTarget(field.x,field.y  )

field:setReferencePoint( display.CenterReferencePoint )

                            

planet = display.newImageRect( “Earth.png”,40,40 )

planet:scale( -2, -2 )

planet.name = “magnet”

planet.x = field.x  ; planet.y = field.y

physics.addBody( planet, “static”, { bounce=0, radius=31.75, filter=magnetFilter } )

secondField = display.newImageRect(“field.png”, 180,180 )

secondField.name = “field”

physics.addBody( secondField, “static”, { isSensor=true, radius=90, filter=fieldFilter } )

secondField.x = 300

secondField.y = 240

secondPlanet =  display.newImageRect(“Earth.png”, 40,40 )

secondPlanet:scale(-2,-2)

secondPlanet.name = “magnet”

secondPlanet.x = secondField.x

secondPlanet.y = secondField.y

physics.addBody( secondPlanet, “static”, { bounce=0, radius=31.75, filter=magnetFilter } )

magnet2 = display.newImageRect( “magnet.png”,70,70 )

magnet2.name = “magnet”

magnet2.isSensor = true

magnet2.x = display.contentCenterX - 220 ; magnet2.y = display.contentCenterY

–physics.addBody( magnet2, “static”, { bounce=0,radius = 40,  filter=magnetFilter } )

                            

                            

end

setupWorld()

                            

                            

                            

                            

                            

local function objectCollide( self, event )

                            

local otherName = event.other.name

            

local function onDelay( event )

local action = “”

if ( event.source ) then action = event.source.action ; timer.cancel( event.source ) end

                            

if ( action == “makeJoint” ) then

self.hasJoint = true

self.touchJoint = physics.newJoint( “touch”, self, self.x, self.y )

self.touchJoint.frequency = magnetPull

self.touchJoint.dampingRatio = 0.0

self.touchJoint:setTarget(self.x,self.y  )

                            

                            

elseif ( action == “leftField” ) then

self.hasJoint = false ; self.touchJoint:removeSelf() ; self.touchJoint = nil

else

                            

end

end

                            

if ( event.phase == “ended” and otherName == “screenBounds” ) then

local tr = timer.performWithDelay( 10, onDelay ) ; tr.action = “leftScreen”

elseif ( event.phase == “began” and otherName == “magnet” ) then

transition.to( self, { time=400, alpha=0, onComplete=onDelay } )

self.hasJoint = false ; self.touchJoint:removeSelf() ; self.touchJoint = nil

self:removeSelf( )

self = nil

elseif ( event.phase == “began” and otherName == “field” and self.hasJoint == false ) then

local tr = timer.performWithDelay( 10, onDelay ) ; tr.action = “makeJoint”

elseif ( event.phase == “ended” and otherName == “field” and self.hasJoint == true ) then

local tr = timer.performWithDelay( 10, onDelay ) ; tr.action = “leftField”

end

                            

end

    local function newObj ()

                            

                            

    obj = display.newImageRect( “object.png”, 48, 48 )

   physics.addBody( obj, { density = 15,bounce=0, radius=12, filter=objFilter } )

    obj.x = magnet2.x

   obj.y = magnet2.y

   obj.hasJoint = false

   projFiring = falseobj.isBullet = true

  obj.isBodyActive = false

   obj.isVisible = false

   obj.collision = objectCollide ; obj:addEventListener( “collision”, obj )

end  

[/lua]

[bjsorrentino]

Hi Hazza,

At a quick overview, I think you’ll basically need to modify the code from the demo as follows:

1. Instead of just a boolean “hasJoint” flag, you’ll need to turn this into an integer counter. When you add a joint to a “satellite” (it enters a gravity field), increase the count by 1. When it exits the field, subtract 1. This is a similar principle as used in the “Can I Jump?” demo, where you keep count of the collisions on the “jump detector” to make sure that jumping isn’t disabled until the detector is clear of all surfaces, as it might overlap multiple at once.

2. Since you’ll (potentially) be creating multiple touch joints on one satellite, you need some means of identifying them for removal, so that when the object exits the gravity field, it knows to remove the touch joint associated with that planet, not another.

3. Now the key part: when you update the “setTarget”, instead of just looking at one touch joint, you’ll need to loop through all of the touch joints on the satellite and update the target of that joint to the planet it’s tied to.

Hope this helps,

Brent

[harryjnewton]

hey brent

thanks for the advice, i think i understand the problem but just before you told me this ,insead of using the self.x and self.y in the setTarget() i put a variable equal to event.other, like this

local other = event.other  

and then put it in the 

self:setTarget(other.x,other.y)  

and after that everything was working perfectly. can i use that as a solution or will it cause trouble?

thanks for your advice.

[bjsorrentino]

Yes, that seems logical enough.

[bjsorrentino]

Hi Hazza,

At a quick overview, I think you’ll basically need to modify the code from the demo as follows:

1. Instead of just a boolean “hasJoint” flag, you’ll need to turn this into an integer counter. When you add a joint to a “satellite” (it enters a gravity field), increase the count by 1. When it exits the field, subtract 1. This is a similar principle as used in the “Can I Jump?” demo, where you keep count of the collisions on the “jump detector” to make sure that jumping isn’t disabled until the detector is clear of all surfaces, as it might overlap multiple at once.

2. Since you’ll (potentially) be creating multiple touch joints on one satellite, you need some means of identifying them for removal, so that when the object exits the gravity field, it knows to remove the touch joint associated with that planet, not another.

3. Now the key part: when you update the “setTarget”, instead of just looking at one touch joint, you’ll need to loop through all of the touch joints on the satellite and update the target of that joint to the planet it’s tied to.

Hope this helps,

Brent

[harryjnewton]

hey brent

thanks for the advice, i think i understand the problem but just before you told me this ,insead of using the self.x and self.y in the setTarget() i put a variable equal to event.other, like this

local other = event.other  

and then put it in the 

self:setTarget(other.x,other.y)  

and after that everything was working perfectly. can i use that as a solution or will it cause trouble?

thanks for your advice.

[bjsorrentino]

Yes, that seems logical enough.