Artwork and code are separately licensed. Art can be CC-BY-SA, but code can be another license. Any art derived from CC-BY-SA art must also be CC-BY-SA, but game code is rarely derived from artwork. This part bears repeating:
GAME CODE IS RARELY DERIVED FROM ARTWORK. Unless you took an art asset, and somehow morphed it into code or an AI script, then sure, that code is derived from the artwork and must be licensed as a derivative of the artwork. Otherwise, the code is not a derivative of the artwork and does not inherit the license.
This is even supported by some of the available information from the Free Software Foundation:
http://wesnoth.org/forum/viewtopic.php?p=108802#108802:"If the "content" does not contain any code -- so that it only has maps, sound, graphics, and so on -- then you can release such content for a GPLed game engine under a proprietary license..."
In most cases, games can have separate licenses for Code and Data. Assets are usually data.
However, this is not a short discussion. It has been hashed out many times before. I would recommend reading the existing discussions (and contributing to those discussions) before starting yet another identical topic about how CC-BY-SA artwork affects game code and engine license:
I used regular floor tiles (bottom layer) to lay down the base [indicated in RED]
Then I used the wall corner parts on top of that (2nd/top layer) to get the wall notch [indicated in GREEN]
Then for the glowing light I used the glow from the north cave opening, but flipped the tiles vertically. [indicated in BLUE] I don't know if your game engine can do vertical tile flips, but the ones I use can, and if not, they should be easy to add by just opening the tileset in gimp or whatever, copying those tiles, and flipping them.
This is what I was referring to. A north-door on the south side of a south wall. FF 4:
Possible with the tileset above by using the north cave entrance on a south wall.
This is what I beleive you were referring to. A notch or steps cut into the south wall. Also FF 4:
Also possible with the tileset above by using the wall edge tiles to carve a notch into the south wall as seen in my pic above.
Please note I say "GPL artwork requires GPL code is debatable", not "saying GPL artwork requires GPL code is incorrect".
At least in part, it depends on...
... how the art collection is packaged in the game,
... how the author wants their work to be distributed.
One of the main arguments is in #1, where artwork is packaged as game data which is separate from game code. Data in GPL'd applications do not need to be GPL as well, and conversely GPL'd data does not require the application that loads it to be GPL as well.
For example: Loading GPL graphics (the data) into Photoshop (non-GPL code) is not a violation. The derivative output (modified graphics) is still GPL, but Photoshop itself doesn't need to be GPL code just for having loaded GPL data. This isn't a perfect example since it is user-loaded GPL'd data and we're talking about developer loaded GLP'd data, but it illustrates what I'm referring to when I say Data vs Code.
There are some instances, depending on how your game code deals with assets, that the code should be GPL due to the way the GPL assets are incorporated into the game's code, but most game engines can load assets unincorporated or as separate collections of data. This is not intended as a loophole, but it does make a difference and I would even say it is how the GPL is intended to operate: GPL affects code, but not data, and art assets are usually data.
The argument for #2 is that you want to respect the artists wishes regardless of the technical interpretation of the license. It is debatable either way, which means it isn't 100% clear in all situations. Therefore:
If you are a developer seeking to use GPL assets in your non-GPL project, you should ask the artist if they're cool with that. You can still get sued by a pissed-off artist even if your lawyer says you're right.
If you're an artist that would like your GPL work to only be used with GPL code, you should say so on your asset submission page. Just setting the license to GPL is no guarantee the downloader will know that it should only be used with GPL code.
@SavedByZero: how would that be displayed in a 3/4 perspective? This isn't true-overhead or "vanishing-point" overhead view like legend of zelda. The "camera" is tilted slightly to the south, so you're actually looking both down and north at the same time. This is why, in the preview above, you're able to see the rock face of the cave's north wall as if it were a side view. A cave entrance on the south end of a cave would be obstructed by the south-end rock wall.
you could put a north facing entrance, then above that a wall, then above that the rest of the cave that you wanted the entrance to lead to. Would that work? This would imply an entrance through the wall, but it would still be a north-facing entrance on the south side of a south wall.
https://www.gnu.org/licenses/gpl-faq.html"...some programs, particularly video games, can have artwork/audio that is licensed separately from the underlying GPLed game...."
Admittedly, the scenarios outlined are GPL code using non-GPL art, not the other way around.
I am confident there was a clarification that Bart was basing our own FAQ on, but it may have been between Bart and FSF, not a public forum. Looking for other references...
"Using GPL licensed artwork requires you to release your game under GPL too,..."
Debatable (though I'd rather not). The Free Software Foundation has clarified that use of art does not trigger the GPL's linking requirement. In most cases, the artwork must also be GPL, but the game code need not be. This kind of "well technically..." response is ultimately why claudeb recommends avoiding GPL entirely and why LDAsh recommends consulting the author directly... and it's why I agree with both of them. :/
1. No. It must be CC-BY-NC. Also, I don't believe -SA is more restrictive than -NC.
2. No. -NC is a nightmare. The technicalities go on for days. Putting a free game on a site that has ads could be a violation. You can always ask the author if they're ok with your intended use, but I wouldn't rely on the courts to decide what trivial source of revenue from a completely indirect association constitutes "commercial".
Yes it is fine with other license (except -ND possibly). Yes, -NC generally ends up being more restrictive, even for non commercial applications.
Sorry if this is not the news your were hoping for. Then again, I'm not a lawyer. The best way to use -NC is to contact the author directly and ask if they're cool with how you plan to use it. Even if your usage technically violates the legalise, that doesn't matter as long as the author is ok with it. Get it in writing* and in very clear terms, though.
*A copy of an email showing timestamp and both to: and from: addresses usually counts as "in writing"
I don't believe that is necessarily an accurate interpretation.
See this discussion: https://opensource.stackexchange.com/questions/173/what-do-i-need-to-sha...
Artwork and code are separately licensed. Art can be CC-BY-SA, but code can be another license. Any art derived from CC-BY-SA art must also be CC-BY-SA, but game code is rarely derived from artwork. This part bears repeating:
GAME CODE IS RARELY DERIVED FROM ARTWORK. Unless you took an art asset, and somehow morphed it into code or an AI script, then sure, that code is derived from the artwork and must be licensed as a derivative of the artwork. Otherwise, the code is not a derivative of the artwork and does not inherit the license.
This is even supported by some of the available information from the Free Software Foundation:
As well as this clarification:
This was primarily in reference to GPL, but I believe it applies to CC-BY-SA as well, especially since CC-BY-SA is on the FSF "list of free licenses" as well as being "one-way compatible" with GPL: https://www.fsf.org/blogs/licensing/cc-by-4-0-and-cc-by-sa-4-0-added-to-...
In most cases, games can have separate licenses for Code and Data. Assets are usually data.
However, this is not a short discussion. It has been hashed out many times before. I would recommend reading the existing discussions (and contributing to those discussions) before starting yet another identical topic about how CC-BY-SA artwork affects game code and engine license:
Here are the tiles I used to make it:
Hope that helps! :)
This is what I was referring to. A north-door on the south side of a south wall. FF 4:

Possible with the tileset above by using the north cave entrance on a south wall.
This is what I beleive you were referring to. A notch or steps cut into the south wall. Also FF 4:

Also possible with the tileset above by using the wall edge tiles to carve a notch into the south wall as seen in my pic above.
Ah, yes like FFIV. I figured those were too subtle, but if that sort of thing is acceptable, they're already in the tileset.
Like this?
Please note I say "GPL artwork requires GPL code is debatable", not "saying GPL artwork requires GPL code is incorrect".
At least in part, it depends on...
One of the main arguments is in #1, where artwork is packaged as game data which is separate from game code. Data in GPL'd applications do not need to be GPL as well, and conversely GPL'd data does not require the application that loads it to be GPL as well.
For example: Loading GPL graphics (the data) into Photoshop (non-GPL code) is not a violation. The derivative output (modified graphics) is still GPL, but Photoshop itself doesn't need to be GPL code just for having loaded GPL data. This isn't a perfect example since it is user-loaded GPL'd data and we're talking about developer loaded GLP'd data, but it illustrates what I'm referring to when I say Data vs Code.
There are some instances, depending on how your game code deals with assets, that the code should be GPL due to the way the GPL assets are incorporated into the game's code, but most game engines can load assets unincorporated or as separate collections of data. This is not intended as a loophole, but it does make a difference and I would even say it is how the GPL is intended to operate: GPL affects code, but not data, and art assets are usually data.
The argument for #2 is that you want to respect the artists wishes regardless of the technical interpretation of the license. It is debatable either way, which means it isn't 100% clear in all situations. Therefore:
@SavedByZero: how would that be displayed in a 3/4 perspective? This isn't true-overhead or "vanishing-point" overhead view like legend of zelda. The "camera" is tilted slightly to the south, so you're actually looking both down and north at the same time. This is why, in the preview above, you're able to see the rock face of the cave's north wall as if it were a side view. A cave entrance on the south end of a cave would be obstructed by the south-end rock wall.
you could put a north facing entrance, then above that a wall, then above that the rest of the cave that you wanted the entrance to lead to. Would that work? This would imply an entrance through the wall, but it would still be a north-facing entrance on the south side of a south wall.
This discussion regarding a conversation with FSF is a start: http://wesnoth.org/forum/viewtopic.php?p=108802#108802
Also, this blurb from the FSF FAQ:
Admittedly, the scenarios outlined are GPL code using non-GPL art, not the other way around.
I am confident there was a clarification that Bart was basing our own FAQ on, but it may have been between Bart and FSF, not a public forum. Looking for other references...
Debatable (though I'd rather not). The Free Software Foundation has clarified that use of art does not trigger the GPL's linking requirement. In most cases, the artwork must also be GPL, but the game code need not be. This kind of "well technically..." response is ultimately why claudeb recommends avoiding GPL entirely and why LDAsh recommends consulting the author directly... and it's why I agree with both of them. :/
1. No. It must be CC-BY-NC. Also, I don't believe -SA is more restrictive than -NC.
2. No. -NC is a nightmare. The technicalities go on for days. Putting a free game on a site that has ads could be a violation. You can always ask the author if they're ok with your intended use, but I wouldn't rely on the courts to decide what trivial source of revenue from a completely indirect association constitutes "commercial".
Yes it is fine with other license (except -ND possibly). Yes, -NC generally ends up being more restrictive, even for non commercial applications.
Sorry if this is not the news your were hoping for. Then again, I'm not a lawyer. The best way to use -NC is to contact the author directly and ask if they're cool with how you plan to use it. Even if your usage technically violates the legalise, that doesn't matter as long as the author is ok with it. Get it in writing* and in very clear terms, though.
*A copy of an email showing timestamp and both to: and from: addresses usually counts as "in writing"
I'm afraid so. Though, as MNDV said, it makes for a fascinating thought experiment.
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