Designing Games with Game Maker - YoYo Games

speed Its current speed (pixels per step).
friction Current friction (pixels per step).
gravity Current amount of gravity (pixels per step).
gravity_direction Direction of gravity (270 is downwards).
motion_set(dir,speed) Sets the motion with the given speed in direction
dir.
motion_add(dir,speed) Adds the motion to the current motion (as a
vector addition).
There are a large number of functions available that help you in defining your motions:
place_free(x,y) Returns whether the instance placed at position(x,y) is
collision-free. This is typically used as a check before actually moving to the
new position.
place_empty(x,y) Returns whether the instance placed at position (x,y)
meets nobody. So this function takes also non-solid instances into account.
place_meeting(x,y,obj) Returns whether the instance placed at position
(x,y) meets obj. obj can be an object in which case the function returns true is
some instance of that object is met. It can also be an instance id, the special
word all meaning an instance of any object, or the special word other.
place_snapped(hsnap,vsnap) Returns whether the instance is aligned
with the snapping values.
move_random(hsnap,vsnap) Moves the instance to a free random, snapped
position, like the corresponding action.
move_snap(hsnap,vsnap) Snaps the instance, like the corresponding
action.
move_wrap(hor,vert,margin) Wraps the instance when it has left the
room to the other side. hor indicates whether to wrap horizontaly and vert
indicates whether to wrap vertically. margin indicates how far the origin of
the instance must be outside the room before the wrap happens. So it is a
margin around the room. You typically use this function in the Outside event.
move_towards_point(x,y,sp) Moves the instances with speed sp toward
position (x,y).
move_bounce_solid(adv) Bounces against solid instances, like the
corresponding action. adv indicates whether to use advance bounce, that also
takes slanted walls into account.