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Platformer with Level Editor

 import QtQuick 2.0
 import Felgo 3.0

 Item {
   id: undoHandler

   // the array, which holds all undoObjects
   property var undoArray: []

   // the pointer, which points at the current position in the
   // undoArray
   property int pointer: -1

   onPointerChanged: console.debug("undo pointer: "+pointer)

   // create a new undoObject with a set of properties
   function createUndoObject(properties) {
     // create UndoObject component
     var component = Qt.createComponent("../undo/UndoObject.qml")

     // create object in gameScene with properties
     var undoObject = component.createObject(gameScene, properties)

     return undoObject
   }

   // add new undoObject to array
   function push(undoObjectList) {
     // before adding a new undoObject, all actions higher than the
     // pointer are removed
     if(undoArray.length > pointer + 1)
       undoArray.splice(pointer+1, undoArray.length)

     // add undoObjectList as element to undoArray
     undoArray.push(undoObjectList)

     // update pointer
     pointer++
   }

   // undo action where pointer points at
   function undo() {
     // if the pointed at undoObject exists...
     if(undoArray[pointer]) {

       // ...undo all actions in this entry
       for(var i=0; i<undoArray[pointer].length; i++) {
         undoArray[pointer][i].undo()
       }

       // update pointer
       pointer--
     }
     else {
       console.debug("nothing to undo")
     }
   }

   // redo action next to where pointer points at
   function redo() {
     // if the undoObject next to the pointed at undoObject exists...
     if(undoArray[pointer+1]) {

       // ...redo all actions in this entry
       for(var i=0; i<undoArray[pointer+1].length; i++) {
         undoArray[pointer+1][i].redo()
       }

       // update pointer
       pointer++
     }
     else {
       console.debug("nothing to redo")
     }
   }

   // print all array elements
   function printArray() {
     console.debug("print undoArray")
     for(var i=0; i< undoArray.length; i++) {
       for(var j=0; j<undoArray[i].length; j++) {
         console.debug(i+"-"+j+": "+undoArray[i][j].target+", "+undoArray[i][j].action+", "+undoArray[i][j].otherPosition+", "+undoArray[i][j].currentPosition)
       }
     }
   }

   // reset undoHandler
   function reset() {
     undoArray = []
     pointer = -1