Designing Games with Game Maker - YoYo Games

Create Effect
With this action you can create all sorts of effects in a very simple way. You specify the type of
effect, e.g. an explosion or smoke, its position, its size and its color and whether it should be
shown below the objects or on top of them. For the rest it works automatic. (For rain and
snow the position is irrelevant as it always falls down from the top of the screen. To get
continuous rain you should create it in each step.) This action is only available in the Pro
Edition.
Using expressions and variables
In many actions you need to provide values for parameters. Rather than just typing a number,
you can also type a formula, e.g. 32*12. But you can actually type much more complicated
expressions. For example, if you want to double the horizontal speed, you could set it to
2*hspeed. Here hspeed is a variable indicating the current horizontal speed of the instance.
There are a large number of other variables that you can use. Some of the most important
ones are:
x the x-coordinate of the instance
y the y-coordinate of the instance
hspeed the horizontal speed (in pixels per step)
vspeed the vertical speed (in pixels per step)
direction the current direction of motion in degrees (0-360)
speed the current speed in this direction
visible whether the object is visible (1) or invisible (0)
image_index this variable indicate which subimage in the current sprite is
currently shown. If you change it and set the speed to 0 (see below) you can
display a fixed subimage.
image_speed this variable indicates the speed with which the subimages are
shown. The default value is 1. If you make this value larger than 1 some
subimages are skipped to make the animation faster. If you make it smaller
than 1 the animation becomes slower by repeating subimages.
score the current value of the score
lives the current number of lives
health the current health (0-100)
mouse_x x-position of the mouse
mouse_y y-position of the mouse