Designing Games with Game Maker - YoYo Games

You might wonder what happens when the instance collides with another instance while it
follows a path. Basically the same happens as when the instance moves with a speed. When
there is a solid instance, the instance is placed back at its previous location. When both
instances are not solid they are placed at their new positions Next the collision event(s) are
executed and it is checked whether the collision has been resolved. If not and the other
instance is solid the instance will stop, as it should (assuming there is a collision event
defined). Also, the path_position variable is not increased. When the blocking instance
disappears the instance will continue to follow its path. To handle collisions yourself the
variable path_positionprevious can be useful. It holds the previous position for the path
and you can set the path position to this variable to avoid advancing along the path.
The path event
As described above, you can indicate what must happen when the instance reaches the end of
the path. At this moment also an End of Path event occurs. You can find it under the Other
events. Here you can place actions. For example, you might want to destroy the instance, or
let it start a new (different) path.
Time Lines
In many games certain things must happen at certain moments in time. You can try to
achieve this by using alarm events but when things get too complicated this won't work any
more. The time line resource is meant for this. In a time line you specify which actions must
happen at certain moments in time. You can use all the actions that are also available for the
different events. Once you create a time line you can assign it to an instance of an object. This
instance will then execute the actions at the indicated moments of time. Let us explain this
with an example. Assume you want to make a guard. This guard should move 20 time steps to
the left, then 10 upwards, 20 to the right, 10 downwards and then stop. To achieve this you
make a time line where you start with setting a motion to the left. At moment 20 you set a
motion upward, at moment 30 a motion to the right, at moment 50 a motion downwards and
at moment 60 you stop the motion. Now you can assign this time line to the guard and the
guard will do exactly what you planned. You can also use a time line to control your game
more globally. Create an invisible controller object, create a time line that at certain moments
creates enemies, and assign it to the controller object. If you start to work with it you will find
out it is a very powerful concept.