|index||The index of the background to duplicate.|
This function will return the index of a newly created
background that is a duplicate (copy) of the one input as the
"index" argument. If the function fails, -1 is returned.
NOTE: When you duplicate a background in GameMaker: Studio you must remember to remove it again (with background_delete) when no longer needed, otherwise there is risk of a memory leak which will slow down and eventually crash your game.
new_bck = background_duplicate(background_index)
The above code duplicates the background currently being used as the background index of the current room and stores the index for this new background in the variable "new_bck".