Add an option to create atlases out of big spritesheets and not only from hundreds of standalone textures

[ajustsomebody]

for instance if one ever wanted to convert a spritesheet into a libgdx atlas they would first need to slice it using some application, which is really just extra work compared to if it was already implemented within the app, so there are my 2 suggestions:

1. add option to slice textures from a big texture inside the app
2. add options to create regions out of selected areas from some big texture like spritesheets

[ajustsomebody]

i was literally going to suggest this, i dont remember if i created this issue or not, but i recall writing this text, just not as a post, yet alone 3 days ago, and https://github.com/crashinvaders/gdx-texture-packer-gui/issues/123 doesn't even show up in my history from last 3 days

[metaphore]

which is really just extra work compared to if it was already implemented within the app

Unfortunately I cannot take this work on myself instead :stuck_out_tongue: Well at least unless there's somewhat high demand amongst users. I don't really think it's quite a frequent case when anyone wants to import a sprite sheet. And by far it's not the most trivial feature, as a sprite sheet can be laterally anything, almost like an atlas.

So I'm afraid I'm going to pass on this one, unless someone else would want to get their hands dirty and implement it.

FYI There's the atlas unpacker tool available in the app. It support only libgdx atlas format, but depends on your case you may get away with it.