question

Double click on the taskexecuter object. A list like structure opens to show the properties of the object. Look for triggers. Expand the triggers list entry. Look for a green plus icon to add triggers. Add an On Load trigger. Now you will have created a trigger. At the trigger you look for a parchment roll icon on the right to open the source code, because you need to do some coding.

Basic knowledge of object tree structure: Any loaded item is becoming a subnode of an object. If you want to know if an object is empty or has already got some content, you can get the value of content by the property length on the subnodes of the object. In a trigger is the reference to the object that is triggered called “current”.

current.subnodes.length

Gets you the number of subnodes (here items) of current. Another reference or pointer in the trigger is “item“. It is a reference to the item that is loaded.

if the item gets loaded, then you can simply set its position by the property location by a variable of Vec3 datatype.

item.location = Vec3(0,0,1);

if the item is loaded as second and above then the reference of the previous item is a treenode property of the tree structure. But the treenode datatype is a parent class of Object and thus does not contain a indirect casting into the class Object.

item.prev.as(Object).location.z

Gets you the z value of previous item in the subnode of the taskexecuter.

Now to an example to set locations of items in the taskexecuter. The first item stays where it is placed to.

if(current.subnodes.length > 1) // content of taskexecuter > 1 then do 
  { // statement block begins
     item.location.x = item.prev.as(Object).location.x+item.prev.as(Object).size.x/2;
     // set the x location to the half size of previous item
     item.location.z = item.prev.as(Object).location.z+item.prev.as(Object).size.z;
    // stacks the item on top of previous item
  } // statement blocks ends

The center of coordinate origin is by default the upper left corner at the bottom of an object.