Add ability to specify which cells/chunks to render instead of the entire map

[TheoBearDB]

Love this tool you've made! I did have one suggestion:

It would be very nice to have the ability to select specific parts of the map you'd like to render instead of having to render the entire map each time. This would be especially nice for situations where parts of the map change, but others don't, and would significantly cut down on time to render and file size. It'd also be nice to use this function for testing different changes in the configuration file to find what works best for each situation.

Also being able to set a range of what cells to render would be incredibly useful as well!

[cff29546]

Rendering part of the map can be a useful feature, but I’m currently struggling to find a clean solution for the isometric map. Since the game data is isometric and the output tile is square, once you determine the expected render range, there will always be a border where some tiles contain only half textures and half empty space. This issue will also affect the upper-level thumbnails, resulting in them appearing incomplete. Consequently, when we attempt to continue render next time, it will be difficult to identify which tiles are only partially rendered which needs a rerender.