There's a well-known GPL3 game on Google Play called Pixel Dungeon by watabou (which includes a game engine by watabou called noosa which is also GPL3), and it accepts donations in the app. The game has been forked by many programmers, in particular by Nyrds to Remixed Pixel Dungeon, where they added unlockable perks for donating, as well as advertisements and IAP.I've been working on my own version forked from RPD, and I plan to make it more significantly different from its forerunners than any of the variants I've found online. I started from RPD rather than PD because RPD added a number of features I wanted to cannibalize. I've removed the ads and IAP, but I'm leaving the donation option in and possibly some donation perks.I'm making a lot of changes to the system, and for my own sanity I've been refactoring the entire structure of the code base: it no longer uses same the directory structure watabou or Nyrds set up, so at a glance it isn't obvious anymore from the structure of the code alone 'who did what' exactly. I understand enough about GPL3 that I know I need to provide users with a link to my own code (which I'll keep on github), and that's not a problem.My question is this: how much trouble do I need to go to in order to properly credit watabou and Nyrds for what they've already done? Is it sufficient for me to mention them both, knowing that the forks on Github allow them to be located by anyone who visits my personal code source, since the trail of forks leads back to both of them? Or do I need to provide and maintain a set of links to the authors' and their work, which might require upkeep on my part?My hope is that absorbing others' code into my own directory structure (rather than keeping it in com.watabou.*, etc.) isn't going to cause me a legal headache. I just prefer being able to organize the code as I see fit, and toss the bits that I never plan to use, since I can always access it again through Github if need be.
How much access to the original code of a GPL-sourced project do I need to provide, personally?
gpl;gpl 3
I'm not aware of any requirement to credit previous authors, aside from keeping their copyright notices intact.I suggest you copy their notice of rights, and the warranty disclaimer to your LICENSE file:This program is free software: you can redistribute it and/or modify  it under the terms of the GNU General Public License as published by  the Free Software Foundation, either version 3 of the License, or  (at your option) any later version.This program is distributed in the hope that it will be useful,  but WITHOUT ANY WARRANTY; without even the implied warranty of  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the  GNU General Public License for more details.The thing to be careful about is whether or not they include:...or (at your option) any later version.For the sake of courtesy you could add the following to your LICENSE file:the program's name and version number when you forkedtheir copyright notice from the code (this also gives a date)some appropriate linkThe original codeYou could note the latest commit ID (e.g. ca458a2).Then you could offer the ability to browse or directly download the original code:  https://github.com/watabou/pixel-dungeon/tree/ca458a2 (browse)https://github.com/watabou/pixel-dungeon/archive/ca458a2.zip (direct download)