Apply different parts of texture atlas to <Instance /> depending on coordinates

[Resaki1]

Hi all!

I'm currently trying to create a game with a, infinite, procedurally created map. For performance reasons, I'm using instancing for the Boxes that make up the map. Everything works great, except that I can't figure out how to map different parts of my texture atlas to the Boxes depending on the coordinates.

I tried to create a minimal example here: https://codesandbox.io/s/hardcore-butterfly-q22348?file=/src/Map.js

The part where I update the map and move the Boxes is not included. The full repository can be found here, though the code might be kinda messy: https://github.com/Resaki1/taal

Can someone help me figuring out how to properly map the textures? I found some similar examples online, though they are all for vanilla Three.js, and I'm a beginner and have a hard time transferring those to my r3f code...