0.12.4 includes a significant rewrite of large parts of the core game engine. Bits that I didn’t like had started to build up, and some plans I have for new game modes looked to be quite difficult to implement because of decisions I made earlier that seemed like a good idea at the time.

The current state of the engine is now much better, however the process does make me nervous. The changes affect not just how the engine plays the game, but also how data is saved and loaded. And people generally don’t like their save games being corrupted.

So as part of the work for this version I also wrote a tool (that I have been intending to write for a while) that checks for save game compatibility. The idea is the tool creates games with various combinations of settings, plays them through (with the easy AI) and saves the result. As part of the normal automated tests I run with each version, these save games are then loaded, the moves replayed, and the result compared with the previous result. Any discrepancies are failures that I can investigate.

Importantly, the initial set of games is based on running the tool before the big engine changes. Unfortunately (or perhaps fortunately) it discovered a bug straight away. Loading a game with “free turn” set to true (i.e. any of the Chain game modes) would not always pick up the “free turn” setting (this was fixed in 0.12.3).

So the plan is every time I add a new game mode (or change the engine significantly), I generate a new set of save files, and during every release the current set of save files is checked for compatibility. Hopefully this should keep everyone happily saving and loading.