Blender3D GameKit Lua Plane Top Bottom Constraint

The top bottom constraint is a bit tricky. As camera keeps moving with plane. I used camera as a reference to calcuate the top and bottom screen edge.
1. Get camera position
2. Calculate current top edge Y location
3. Calculate current bottom edge Y location
4. Compare with current plane location, and return signals, -1 as plane too low, 1 as plane too high, 0 for plane inside the screen
5. feed the signal and mouse movement to function edgeMoveFilter, which only permit plane move toward centre if it is on edge
The code is below and red marks are comments.
******Oninit.lua****************

    --Global variable

    --set touch move parameters

    Sensitivity = 0.005

    --invert = -1 -> is inverted

    Invert = 1

    Threshold=3.5

 -- Plane Contrain

    Xmin = -0.87

    Xmax = 0.87

 -- Plane Top Bottom Constrain

    Ymin = -1.50

    Ymax = 1.30

--filter movement so plane will only move towards center if touchs edge

function edgeMoveFilter(limitSignal,oldX)

    if limitSignal == -1 and oldX > 0 then

        return oldX

    elseif limitSignal == -1 and oldX < 0 then

        return 0

    elseif limitSignal == 1 and oldX >0 then

        return 0

    elseif limitSignal ==1 and oldX <0 then

        return oldX

    end

        return 0

end   

--check if over boundary on Y axis

function YoverLimit(obj,cameraObj)

    local vec3 = obj:getPosition()

    local cameraV = cameraObj:getLinearVelocity()

    --get camero position

    local cameraP = cameraObj:getPosition()

    --calculate bottom edge ;ocation

    local nextYmin = cameraP.y+Ymin

    --calculate top edge location

    local nextYmax = cameraP.y+Ymax

    --check whether plane is on edge and return signals

    if vec3.y < nextYmin then

        return -1

    elseif vec3.y > nextYmax then

        return 1

    else 

        return 0

    end

end

--endNew-----------

function XoverLimit(obj)

    local vec3 = obj:getPosition()

    if vec3.x < Xmin then

        return -1

    elseif vec3.x > Xmax then

        return 1

    else

        return 0

    end

end

function printPosition(obj)

    local vec3 = obj:getPosition()

    dPrintf("position x: " .. vec3.x)

    dPrintf("position y: " .. vec3.y)

    dPrintf("position z: " .. vec3.z)

    

end    

function velocityCap(v,vmax)

    if (v>vmax) then

        return vmax

    elseif (v < -vmax) then

        return -vmax

    else return v

    end

end

******planeTouchMove.lua****************  

mouse=OgreKit.Mouse()

scene = OgreKit.getActiveScene()

play = scene:getObject("plane")

--new--get camera objcet

camera = scene:getObject("Camera")

--end new---------------------------

logicM = OgreKit.LogicManager()

myLogicObject = logicM:getObject("plane")

mySensor = myLogicObject:getSensor("Collision")

maxVelocity=0.08

mouse:capture()

--print current plane posistion on screen

--printPosition(play)

--using threshold to filter out unwanted small touch movement

if ((mouse.xrel>Threshold or mouse.xrel<-Threshold)or(mouse.yrel>Threshold or mouse.yrel<-Threshold)and (not(play.touchBoundary))) then

      velocityY=velocityCap((mouse.yrel) * Sensitivity, maxVelocity)

      velocityX=velocityCap((mouse.xrel) * Sensitivity, maxVelocity) 

      --new----------------------

      --check if plane over screen boundary 

      limitSignalX = XoverLimit(play)

      limitSignalY = YoverLimit(play,camera)

      --the X Y directions are swap as the screen is in landscape

      if limitSignalX==0  and limitSignalY == 0 then

      --when plane is inside boundary

        play:translate(-velocityY* Invert,-velocityX * Invert,0)

      else

      --when plane touches boundary it can only move away from boundrary

        newY = edgeMoveFilter(limitSignalX,-velocityY * Invert)

        newX = edgeMoveFilter(limitSignalY,-velocityX * Invert)

        play:translate(newY,newX,0)

      end

      --end new---------------------

end