Alright, I think this is it. Added addtiledef2 img,dest,x,y; and addtiledef2("img","dest",x,y); support. However, right now it scans through the levels, and doesn't use tiledefsOffline.txt. I don't seem to have the file, so I'm assuming it doesn't work or something *shrug*. So make sure you have at least one NPC on the overworld that defines the tiledefs.
I think this is pretty complete now, should be able to render most maps efficiently
I also included a shortcut in the folder that increases the memory heap for the program. I'm not sure if the shortcut will work for anyone else, but you can try it. It's at 1300mb, but if you right click the short cut and go into properties you can change it via changing:
-Xmx1300m
to something like
-Xmx2000m
This will allow the program more memory to render larger maps. But if you raise the number too high the program won't even manage to run.
edit: I've updated it to catch the memory errors, so it shouldn't just hang at "Generating..." if not enough memory is allocated. I've also included a BAT that lets you define the memory allocation before it starts the program.