⚠ 2026-07-25 — the observations below are correct, and the mechanism behind them is now reversed. Full write-up in "TL2 .MOD Packing, Fully Analyzed" §8.2. In short:

  • “Function 1 runs before Function 2” is simply the order inside CreateMod (sub_103FA610): the pathing step (Pathing_RegenAll_worker @0x10018750) runs before the LAYOUT→BINLAYOUT compile (sub_1029C9A0).
  • MPP needs BINLAYOUT because the pathing step drives the runtime level loader (CLevel_LoadLevelData @0x1020AB90), not a text parser, and the loader only eats .BINLAYOUT. No BINLAYOUT → level load fails → it degrades to a default 50×50 box → an all-0xFF stub.
  • The stub is 2524 bytes = 24-byte header + 50×50, which matches the “exact 2.5kb” below. The quoted header bytes 4B 00 00 00 4B 00 00 00, though, contradict that size (0x4B = 75, and 75×75 would be 5649 bytes); a 50×50 header reads 32 00 00 00 32 00 00 00. Trust the size.
  • The offline packer has none of this: it compiles BINLAYOUT from text on every run and bakes MPP offline, so there is no stale-intermediate chicken-and-egg and no need to build twice.

I have recently done some tests regarding the .MPP files.
(Please be aware MPP files will only be generated for LAYOUT files in the LAYOUTS folder) It is quite common that developers like to maintain their mod workspace clean.
So, we usually clean up the .BIN*, .MPP files and …
But in some specific scenarios, it will introduce issues in.
With the following steps, we can reproduce this issue.
(Which normally causing player unable to move after entering a dungeon related to the layout file)

Open GUTs, select a mod let’s say TEST, then before you click build, delete all the “.BIN*”,".MPP" files and …
Then you will notice that all the new generated MPP file size will be exact 2.5kb
They all start with 4B 00 00 00 4B 00 00 00 00 in hex viewer.
To fix this, you will have to build again.

Why this happen? Let’s dig in further.
After some tests, here is the weird logic GUTS uses:
When you open a mod project using GUTS, while initializing GUTS will only invoke Function 2
When you click the build button, GUTS will invoke Function 1 first then Function 2

Function 1

IF BINLAYOUT EXIST:
    Generate MPP from BINLAYOUT
ELSE:
    Generate MPP from DEFAULT(2.5Kb)

Function 2

IF BINLAYOUT EXIST:
    Check CRC32
    IF CHECK PASS:
        Done
    ELSE:
        Generate BINLAYOUT from LAYOUT
ELSE:
    Generate BINLAYOUT from LAYOUT

Scenario 1
You open a mod project in GUTS, you make some changes in LAYOUT file from external editor, you delete BINLAYOUT and MPP files. You click build button. What you will get:
A valid BINLAYOUT file.
An invalid MPP file (Size 2.5Kb start with 4B 00 00 00 4B 00 00 00 00).

Scenario 2
You open a mod project in GUTS, you make some changes in LAYOUT file from external editor, you click build button. What you will get:
A valid BINLAYOUT file.
An invalid MPP file (Cuz it is generated using the out-of-date BINLAYOUT).

It is quite clear now, if you make changes to the LAYOUT file after you open the mod project, you will not be able to get the correct MPP file. You will have to build twice to get the correct one.

Solution?

  • Option 1: Open GUTS after you finish making changes to the LAYOUT files. GUTS’s initialization will update the BINLAYOUT, then when building process, you will get the correct MPP file.
  • Option 2: Build twice