I am going to make a new series of tutorials talking about some mapping stuffs relative to complex events and player / level interactions, or design details like FOF textures offset alignment.

I have a lot of techniques to explain, but I'll let the choice to members.
Please tell me what kind of mapping stuffs you wish me to explain in this tutorial, like a door that only opens if several switches get pressed, up/down/stop switch elevator, appearing/dissapearing things, crumbling FOFs that stands on the floor instead passing through it, and whatever you want else...

Tutorials will be all listed in this post, and I'll send a new message each time I post a new one.

Naming Conventions
First of all, we need some conventions to have efficient tutorials:
-Lines and linedefs are the same thing. It just depends on which map editor you're using. By the way, "linedef" means "line DEFinition".
-When I say "straight linedef", I mean "horizontal or vertical linedef".
-Sometimes I talk about "physical part" of a level or a sector. In this case I'm talking about the level itself, the part of the level that players can see where they can go in (unless if it's a wall of course). Physical parts of the level have their shape directly drawn in the map editor and have an invariable quantity of attributes (properties), like floor and ceilling height, textures, lightning level, special effects, tag,...
-A in-level sector is a sector that is a physical part of the level. More concretely, this is a normal sector.
-A control sector is a sector OUTSIDE THE MAP. This means it isn't a physical part of the level. Here the sector is just used as a way to keep extra informations used by the game for some purposes, like making a moving platform, water, platforms, events, visual effects, etc...

Tutorial 1 - Basics of FOFing
What is a FOF ?
Unlike it is usually said, FOF isn't always the equivalence of platform in 2D games.
And, unlike it is usually said, there is only one type of FOF.

Here is one of the fundamental secrets of the most powerful mapping techniques in srb2.

Tutorial 2 - Basics of Linedefs Executors
Coming soon

Tutorial 3 - Music Changer
I'll start by explaining how to change the background music when a player enters a specific sector.
The easier way is to change the music only for the triggering player (the player who walked in the sector), however it can equally affect every players in the level or in a specific part of the level. In all these cases, I'll assume you made the "physical" part of the sector. Linedefs and lines are the same thing. When I say "straight", I mean "horizontal or vertical".

Triggering player only:
1) Set the triggering sector effect to 64 and give it a new tag (unused of course).
2) Make a control sector.
3) Choose one of its linedefs and give it the tag of step 1, then set its action to 300, or 302 if the music must change only the first time the player comes.
4) Choose another of its straight linedefs, then set its action to 413 (you can eventually change flags to add some effects, check the srb2wiki for that).
5) Still on the same linedef, move one of the vertices to make the linedef having its lenght equal to the tunes (music) number you want to play.

All players:
In progress

Specific part of the level:
Coming soon