Zoom on touch event - lua

Question

I'm trying to put in place a zoom function on touch event. I scale the parent group using transition.to and onComplete move it to the event center. But then at one point it just jumps to the parent group origin. Any ideas?
I'm now pasting a shortened version of the code.
local physics = require( "physics" )
physics.start()
physics.setContinuous( false )
--physics.setScale( 60 )
local height = display.contentHeight
local width = display.contentWidth
local backGround = display.newRect( 0,0,width,height )
backGround:setFillColor(91,91,91)
local allElements = display.newGroup()
local grip = {}
local gripSize = {
-- w: gripwidth, h: gripheight, s: strength required
{w=30, h=20, s=1},
{w=20, h=10, s=1.5},
{w=10, h=10, s=2},
}
local r
local function createTexture()
local originX = 0
local originY = height -75
for i=0,50 do
r = math.random(3)
local x = originX + math.random(width)
local y = originY - math.random(2*height)
grip[i] = display.newRect( allElements, x, y, gripSize[r].w, gripSize[r].h)
grip[i].size = gripSize[r].s
if (r == 1) then
grip[i]:setFillColor(51,255,0)
elseif (r == 2) then
grip[i]:setFillColor(255,51,51)
elseif (r == 3) then
grip[i]:setFillColor(51,51,255)
end
end
end
createTexture()
wallBottom = display.newRect( allElements, 0,height-20,width,20)
physics.addBody(wallBottom, "static", { density=5, friction=0.5, bounce=0.3 } )
head = display.newCircle( allElements, width/2,50,20 )
physics.addBody( head, { density=5, friction=0.5, bounce=0.3 } )
local touchBorder = 20
local function calcTouchOffset( e )
local x, y = 0, 0
if (e.x < touchBorder) then
x = e.x - touchBorder
elseif (e.x > width-touchBorder) then
x = e.x - (width-touchBorder)
end
if (e.y < touchBorder) then
y = e.y - touchBorder
elseif (e.y > height-touchBorder) then
y = e.y - (height-touchBorder)
end
return x, y
end
local function startDrag( e )
local body = e.target
local phase = e.phase
local stage = display.getCurrentStage()
if (e.phase == "began") then
e.target.bodyType = "dynamic"
e.target.hasFocus = true
local x, y = allElements:contentToLocal( e.x, e.y )
e.target.touchjoint = physics.newJoint( "touch", e.target, x, y )
stage:setFocus( e.target )
transition.to( allElements, { time = 200, x= -body.x, y= -body.y, xScale = 2, yScale = 2,})
xOffset, yOffset = 0, 0
return true
elseif (e.target.hasFocus) then
if (e.phase == "moved") then
local x,y = allElements:contentToLocal(e.x, e.y) -- This line is changed
e.target.touchjoint:setTarget( x, y ) -- This line is changed
xOffset, yOffset = calcTouchOffset( e )
else
transition.to( allElements, { time = 200, x = body.x, y = body.y, xScale = 1, yScale = 1, })
e.target.hasFocus = false
e.target.touchjoint:removeSelf()
e.target.touchjoint = nil
stage:setFocus( nil )
xOffset, yOffset = 0, 0
end
return true
end
xOffset, yOffset = 0, 0
return false
end
head:addEventListener( "touch", startDrag )
function allElements:update()
allElements.x, allElements.y = allElements.x - xOffset, allElements.y - yOffset
allElements.x, allElements.y = allElements.x, allElements.y
if (allElements.x > -startX) and ( startX < 0 ) then
allElements.x = -startX
elseif ( routeW < width ) then
allElements.x = 0
elseif ( allElements.x < startX ) and ( startX < 0 ) then
allElements.x = startX
end
--[[if (allElements.x > 0) then
allElements.x = 0
elseif ( routeW < width ) then
allElements.x = 0
elseif ( allElements.x < (width-routeW) ) and ( routeW > width ) then
allElements.x = width-routeW
end ]]--
if (allElements.y > (routeH-height)) and ( routeH > height ) then
allElements.y = routeH-height
elseif ( routeH < height ) then
allElements.y = 0
elseif (allElements.y < 0) then
allElements.y = 0
end
end
function enterFrame()
allElements:update()
end

Answer 1

You just need to update this part:
elseif (e.target.hasFocus) then
if (e.phase == "moved") then
local x,y = allElements:contentToLocal(e.x, e.y) -- This line is changed
e.target.touchjoint:setTarget( x, y ) -- This line is changed
xOffset, yOffset = calcTouchOffset( e )
else
transition.to( allElements, { time = 200, x = 0, y = 0, xScale = 1, yScale = 1, })
e.target.hasFocus = false
e.target.touchjoint:removeSelf()
e.target.touchjoint = nil
stage:setFocus( nil )
xOffset, yOffset = 0, 0
end
return true
end
By replacing x=body.x by x=0 and y=body.y by y=0
Cheers :)