Open the stack script. There is only one of the global variables that we will also need in the stack script, but there are a couple of initializing items we need to cover. Start the stack script with these lines:

global snapdistance

on preopenstack
  if the platform contains "iphone" then iphoneUseDeviceResolution true
end preopenstack

on openstack
  set the compositorType of this stack to "Static OpenGL"
end openstack

The preopenstack handler checks whether the app is on iPhone and requests that the device's native resolution be used. This will make sure that Retina displays show the best quality. The compositorType being set to "Static OpenGL" will help performance.

The interactivity we'll use will make use of touch events. Each touch comes...