Designing Games with Game Maker - YoYo Games

instance_position(x,y,obj) Returns the id of the instance of type obj at
position (x,y). When multiple instances are at that position the first is
returned. obj can be an object or the keyword all. If it does not exist, the
special object noone is returned.
instance_nearest(x,y,obj) Returns the id of the instance of type obj
nearest to (x,y). obj can be an object or the keyword all.
instance_furthest(x,y,obj) Returns the id of the instance of type obj
furthest away from (x,y). obj can be an object or the keyword all.
instance_place(x,y,obj) Returns the id of the instance of type obj met
when the current instance is placed at position (x,y). obj can be an object or
the keyword all. If it does not exist, the special object noone is returned.
The following functions can be used for creating and destroying instances.
instance_create(x,y,obj) Creates an instance of obj at position (x,y).
The function returns the id of the new instance.
instance_copy(performevent) Creates a copy of the current instance.
The argument indicates whether the creation event must be executed for the
copy. The function returns the id of the new copy.
instance_destroy() Destroys the current instance.
instance_change(obj,perf) Changes the instance into obj. perf indicates
whether to perform the destroy and creation events.
position_destroy(x,y) Destroys all instances whose sprite contains
position (x,y).
position_change(x,y,obj,perf) Changes all instances at (x,y) into obj.
perf indicates whether to perform the destroy and creation events.
Deactivating instances
When you create large room, for example in platform games, with a small view, many
instances lie outside the view. Such instances though are still active and will execute their
events. Also when performing collision checks these instances are taken into account. This can
cost a lot of time, which is often not necessary. (For example, often it is not important
whether instances outside the view move.) To solve this problem Game Maker contains some
functions to deactivate and activate instances. Before using them you must though clearly
understand how they work.