Time for action – launching the panda

Let's add a touch event for the panda so that it flings toward the stars. The powerShot object will play a role in helping the player visualize how much power needs to be applied to the panda, before it launches into the air.

Implement touch events for the panda. Create a local function called onScreenTouch() with an event parameter:
```
local onScreenTouch = function( event )
```

With gameIsActive initiated, add in an if statement for when the touch event starts, by using event.phase == "began". During this event, use the "crouch" animation set to prepare panda for launch:

  if gameIsActive then
    if event.phase == "began" and panda.inAir == false then

      panda.y = 225
      panda.isReady = true
      powerShot.isVisible = true
      powerShot.alpha = 0.75
      powerShot.x = panda.x; powerShot.y = panda.y
      powerShot.xScale = 0.1; powerShot.yScale = 0.1

      arrow.isVisible = true

      panda:setSequence("crouch")
      panda:play()

Add an elseif statement for when the touch event ends by using event.phase == "ended". Create a new local function called fling(), which will hold the properties of panda when it is launched toward the star objects. Apply a force opposite to where the touch event is dragged. Scale the powerShot display object outward when the touch event is pulled farther from the character:

    elseif event.phase == "ended" and panda.isReady then

      local fling = function()
        powerShot.isVisible = false
        arrow.isVisible = false

        local x = event.x
        local y = event.y
        local xForce = (panda.x-x) * 4
        local yForce = (panda.y-y) * 4

        panda:setSequence("air")
        panda:play()

        panda.bodyType = "dynamic"
        panda:applyForce( xForce, yForce, panda.x, panda.y )
        panda.isReady = false
        panda.inAir = true

      end

    transition.to( powerShot, { time=175, xScale=0.1, yScale=0.1, onComplete=fling} )

    end

    if powerShot.isVisible == true then

      local xOffset = panda.x
      local yOffset = panda.y

      local distanceBetween = mCeil(mSqrt( ((event.y - yOffset) ^ 2) + ((event.x - xOffset) ^ 2) ))

      powerShot.xScale = -distanceBetween * 0.02
      powerShot.yScale = -distanceBetween * 0.02

      local angleBetween = mCeil(mAtan2( (event.y - yOffset), (event.x - xOffset) ) * 180 / mPi) + 90

      panda.rotation = angleBetween + 180
      arrow.rotation = panda.rotation
    end

  end
end

What just happened?

Once the game is active and the panda has been loaded on the screen, a touch event to launch the panda can be initiated. The panda will go from a "static" physics state to a "dynamic" physics state. The powerShot display object size increases the farther back the panda is pulled by an event touch.

The force from the panda launch is applied by local fling = function(). Launch force is created by xForce and yForce. The panda object is propelled by panda:applyForce( xForce, yForce, panda.x, panda.y ). Notice that the body type changes to "dynamic", so gravity can affect the object.