Designing Games with Game Maker - YoYo Games

Particle motion
Particles can move during their lifetime. They can get an initial speed (or range of speeds) and
direction, and the speed and direction can change over time. Also gravity can be defined that
pulls the particles in a particular direction. The following functions exist for this:
part_type_speed(ind,speed_min,speed_max,speed_incr,speed_wi
ggle) Sets the speed properties for the particle type. (Default all values are
0.) You specify a minimal and maximal speed. A random value between the
given bounds is chosen when the particle is created. You can indicate a speed
increase in each step Use a negative number to slow the particle down (the
speed will never become smaller than 0). Finally you can indicate some
amount of wiggling of the speed.
part_type_direction(ind,dir_min,dir_max,dir_incr,dir_wiggle
) Sets the direction properties for the particle type. (Default all values are 0.)
Again you specify a range of directions (in counterclockwise degrees; 0
indicated a motion to the right). For example, to let the particle move in a
random direction choose 0 and 360 as values. You can specify an increase in
direction for each step, and an amount of wiggling.
part_type_gravity(ind,grav_amount,grav_dir) Sets the gravity
properties for the particle type. (Default there is no gravity.) You specify the
amount of gravity to be added in each step and the direction. E.g. use 270 for
a downwards direction.
Particle systems
Particles live in particle systems. So to have particles in your game you need to create one or
more particle systems. There can be different particle systems (but preferably keep their
number small). For example, if your game has a number of balls and each ball should have a
tail of particles, most likely each ball has its own particle system. The easiest way to deal with
particle systems is to create one and then create particles in it, using the particle types you
specified before. But, as we will see below, particle systems can contain emitters that
automatically produce particles, attractors that attract them, and destroyers that destroy
them.
Once particles are added to a particle system they are automatically updated each step and
drawn. No further action is required. To make it possible that particles are drawn, behind, in