After seeing series of increasingly strange uses of "user events" in GameMaker games for object-bound actions, it came to my attention that most people are only vaguely aware of other ways of doing things, so I decided to write a small blog post on the matter.
There are many uses for these - for example, you might want to have a "take X damage" method on your enemy objects so that it can be varied depending on requirements - some enemies might just take damage, some should retaliate on being hit, some might have a fancy damage reduction formula. Being able to comfortably define/redefine methods on per-object-type basis can help a lot.
Sometimes you might want to pass an instance variable by reference rather than by value - to have a script modify instance variable(s) passed to it without having to return them, or have an instance save a reference to variable(s) that it should change on other instance, or doing anything else that would usually imply using pointers.
But it might seem like GameMaker does not support such things... or does it? Well, we'll make it.
(click to interact)(mouseover/click to play GIF)(click and drag to adjust rectangle size/position/rotation; distance to a circle is shown)
Suppose you have a rotated rectangle and a basic shape that rotation doesn't matter for (such as a point, circle, or a line segment), and you want to check whether the two are intersecting - be that for collision handling, hit testing, or whatever else.
On a glance this might seem like a bother because things are rarely too simple with rotated rectangles, but in this case it isn't - because you can "unrotate" the rectangle.
(click to interact)(mouseover/click to play GIF)(spaceship graphic by Kenney)
Nowadays, most development tools provide ways of setting pivot/center point for imagery - that is, the relative point around which the image will rotate and usually be positioned relative to.
However, ability to define multiple pivot points per image remains relatively uncommon, despite being something that you want to have projectiles fire from a correct point of a sprite, display weapons/attachements at right relative points, or do anything else that demands relative offsets.
This post is about implementing custom timelines in GameMaker.
Admittedly, timelines remain to be one of the more dated features of the software, designed for a specific purpose and kept in their original form for compatibility.
Time to time you'll see someone stopping by on forums to write a big rant about how these are a mess, do not do what they expect them to do, and should be redesigned immediately.
People will usually also argue that doing these things by yourself is too hard.
Since it is far easier than people claim, I decided to write a post about this.