This week marked the beginning of my journey with ScummVM for Google Summer of Code, and I kicked things off by working on the SLUDGE engine.
For those unfamiliar, SLUDGE is an engine that enables developers to create and publish their own point-and-click adventure games. These games are highly script-driven, especially in how they handle input. Keyboard input, in particular, is passed directly to the script, and from there, it’s entirely up to the game developers to define how those inputs are interpreted and used in their game logic.
My main goal for the week was to implement ScummVM’s keymapper support in the SLUDGE engine. However, this came with its own set of challenges.
Each SLUDGE-based game defines its own key bindings for different actions. That meant I had to manually identify the default controls for over 10 supported games. This process was quite time-consuming, as there was no centralized documentation. In some cases, I found the information in the game’s source code, in others through manuals, and occasionally I had to just play through the game and note what each key did.
While this part of the task was tedious, it was relatively straightforward. The real challenge came when I had to figure out when to disable the keymapper.
Why? Because some games allow players to enter custom save file names, which means they need unrestricted keyboard input. If the keymapper remained active during such input modes, it would interfere with typing. Unlike many other engines, SLUDGE doesn’t offer a built-in pause menu or modal state, so each developer handled menus differently.
After some digging through the engine source and various game scripts, I discovered two important functions: `freeze()` and `unfreeze()`. These were used every time a menu was shown or hidden. While not all menus required full keyboard input (most only needed mouse interaction), this discovery gave me a reliable enough hook. I could safely disable the keymapper when a menu was active and re-enable it when gameplay resumed.
With that, I successfully implemented keymapper support for the SLUDGE engine in ScummVM!
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