Mage Game Engine Documentation

Chains of Small Checks

#updateme

This is most likely required for a map's on_load script, but there are other times you might want a chain of small optional behaviors at the beginning of a script. For an example, here are some of the things the BMG2020 main map must check when loaded:

  • Is it a brand new game? If so, branch: put the player in their bedroom in the mage house. (Script diverts to a dead end.)
  • Has Bob Moss's quest been completed? If so, teleport him off screen to hide him. (Resume remainder of script either way.)
  • Has the rake ever been laked? If so, teleport rake to lake. (Resume remainder of script either way.)
  • Has the goat Billy ever been unglitched? If so, unglitch again now. (Resume remainder of script either way.)
  • (more glitch checks)
  • Have the sheep been returned to their pen at some point? If so, return them again now. (Resume remainder of script either way.)
  • Has Bender's ass been restored? If so, restore it again now. (Resume remainder of script either way.)
  • Has the "walk to lodge" cutscene been seen before? If not, play it now. (Script diverts to a dead end.)
  • (more cutscene checks)
  • Is the warp_state enter_from-greenhouse? If so, branch: run the enter_from-greenhouse script, which teleports the player to the greenhouse door and walks the player down a few pixels. (Script diverts to a dead end.)
  • (more warp_state checks)

Unfortunately, the only way to do this is with a lot of tiny scripts. (This is one reason you might want to put on_load in the script name for all scripts like this — so you know what kind of a chain you're looking at.)

flowchart of a series of small scripts

For chains like this, it can be beneficial to aggressively split scripts so that you can quickly and easily identify each step of logic, which makes it easier to tune branching or insert additional checks. Abstracting the initial on_load script will help, too — so the script running the logic check can be named appropriately while allowing the name of the map's on_load script to remain consistent (rather than having to manage the name of the map's on_load script from within Tiled).

To genericize a chain:

  • [Start Script]
    • Run "X Check"
  • [X Check]
    • Check if X happened. If yes, run "Fix X"
    • Run "Y Check"
  • [Fix X]
    • Fix X
    • Run "Y Check"
  • [Y Check]
    • Check if Y happened. If yes, run "Fix Y"
    • Run "Z Check"
  • [Fix Y]
    • Fix Y
    • Run "Z Check"
  • Etc.