Designing Games with Game Maker - YoYo Games

When a ball hits the floor it must change direction. This has to be specified in the collision
event of the ball with the floor. Because there are four different floors we need to put the code
on four different collision events of the ball. But when you make one base floor object and
make this one the parent of the four actual floor objects, you only need to specify the collision
event with this base floor. The other collisions will perform the same event. Again, this saves a
lot of copying.
As indicated, wherever you use an object, this also implies the descendants. This happens
when, in an action, you indicate that the action must be applied to instances of a certain
object. It also happens when you use the with() statement in code (see below). And it works
when you call functions like instance_position, instance_number, etc. Finally, it works
when you refer to variables in other objects. In the example above when you set ball1.speed
to 10 this also applies to ball2, ball3 and ball4.
Masks
When two instances collide a collision event occurs. To decide whether two instances intersect,
the sprites are used. This is fine in most cases, but sometimes you want to base collisions on a
different shape. For example, if you make an isometric game, objects typically have a height
(to give them a 3D view). But for collisions you only want to use the ground part of the sprite.
This can be achieved by creating a separate sprite that is used as collision mask for the object.
Information
The button Show Information gives an overview of all information for the object that can
also be printed. This is particularly useful when you loose overview of all your actions and
events.
More actions
In advanced mode there are a number of additional actions available which will be described
here.
More move actions