port-a-mod

1# Port a mod faithfully
2 
3When porting an existing mod, the original is the spec. A port rarely fails for lack of code. It fails by
4**drift**:
5- values recalled from memory or a wiki;
6- mechanics borrowed from a later rewrite of the same mod;
7- quiet "improvements";
8- renderers that look roughly right;
9- checks that the original made on the client and the port forgot.
10 
11The method below carried a Thaumcraft 4.2.3.5 port from Minecraft 1.7.10 Forge to 1.20.1 Fabric:
12- 859 original classes became about 77,000 lines of port code;
13- 323 GameTests cover it, and scripted real-client scenarios check what tests can't reach;
14- the work spanned many sessions and two agent accounts.
15 
16The field note `knowledge/games/minecraft/porting-thaumcraft-4-1-7-10-forge-to-minecraft-1-20-1-fabric.md` has
17its gotchas. Minecraft-specific mappings are in `references/minecraft-1-7-10-forge-to-1-20-fabric.md`.
18 
19Run the **mod-any-game** loop around this skill (intake, recon, lab, verify, publish, field note). This
20skill replaces its "vertical slice" step with a long series of slices, one per unit of the original.
21Bringing one game's content or mechanics into another game is the **mashup-mods** skill, not this one.
22 
23## Before you start: the license
24The original's code and assets belong to its author. A port is built from them, often from a decompile of
25them, so the original's license decides what of the port can be published. (This isn't legal advice; when
26in doubt, ask the author.)
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