I’m trying to export my maps from Tiled into Game Maker 2. While there is support for 1.4 in Tiled, there is not for 2, so I had to find a plugin. The closest I found was this: https://lazyeye.itch.io/gmtiled
Unfortunately, as the website says, ‘Keep in mind that GMS is only capable of having one tileset per layer, so you may need to create one “master tilesheet” to use if you’re using more than one per layer in Tiled.’
So, my question is, if I have a pre-existing map with three tilesets, how would I make a master tilesheet with the three tilesets, without messing up the ordering in Tiled, and having the maps the exact same?
You could merge the tilesets using an image editor - like GIMP - and then replace each tile of the separate sets using Select Same Tile and the Bucket Fill (+Shift) tools.
Also, welcome to the Tiled forums!
I’m guessing ideally you’d like to keep your tilesets separated while working on your maps and only have a (possibly optimized) “master tileset” generated when exporting your map to Game Maker? This is not possible at the moment but it could certainly be implemented as an export feature (as well as exporting to Game Maker 2 format, of course).
In general Tiled currently can’t modify tileset images and does not currently offer much to help you adjust a map to moving of tiles within an image or to another image, apart from the features mentioned by @Modanung and the “Swap Tiles” action when you select two tiles in a tileset (which swaps all usages of those tiles on the current map).