ctor() {
    // initialize properties that may be required in init
    this._sourceScreenPosition = cc.p();
    this._targetScreenPosition = cc.p();
    this._delta = cc.p();

    // do super ctor
    this._super(RSX.tile_path_attack.frame);
  }
*************************************************************************
AttackPathSprite
var AttackPathSprite = BaseSprite
AttackPathSprite.create()
 - attack path sprites ONLY travel along x axis
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