This was originally published 2020-07-07 as a reward for sponsors of Befriendus

A Domain-Specific Compression Algorithm — as I later found out this is called — is a compression algorithm that uses the specific nature of the target data as a way to efficiently compress it. The more you know about the structure of the data you’re compressing and what tools you have to reconstruct data, the more efficient the system can be.

I wrote a script for the Fansim Engine that does this with character sprites. It takes character poses, identifies the parts that have changed and the parts that stay the same, and creates identical Ren’py displayables that take up dramatically less room.

As is common in Python, the mechanical process of displaying something on screen in Ren’py is at once easy to execute and deceptively complicated to execute correctly.

The Ren’py documentation does a fine job of defining the specifications of position properties, but intuitively understanding how to use those properties can still be hard because it doesn’t include much in the way of examples or elaboration, so here are some of those.