Open source plays a vital role in game development, just as it does in most software projects. Recent data shows that roughly 97% of projects include open source components — not surprising, given the cost-effectiveness and flexibility open source provides. Typically free to use, open source software also allows developers to modify the code for their own needs without facing licensing restrictions or added fees.
However, one of the main hurdles lies in ensuring compatibility between open source solutions and proprietary software or platforms, which can complicate and lengthen the development process. As such, understanding the relevant licenses is crucial. As Chinese General and philosopher Sun Tzu once said, “He will win who has prepared himself.”
The basic premise
Open source, in a legal sense, lacks a strict statutory definition. Instead, it is guided by principles established by the open source Initiative. To qualify as an open source project under these principles, the following criteria must be met:
- Free redistribution
The software must be freely redistributable. Charging license or other fees for its redistribution is not allowed.
- Access to source code
The source code must be openly accessible in some form.
- Modifications and further development
It must be possible to modify and build upon the software, and any redistributed versions should carry the same licensing terms.
- Integrity of the original code
Any requirement to maintain the original code can be met by distributing patches alongside the source code or by publishing modified versions under different names or version numbers.
- No restrictions or discrimination
Licenses cannot discriminate against individuals or groups, or limit how the software is used. Neither can they restrict bundling the software with other programs or the specific technology used to run it.
Although all open source licenses must satisfy the same core requirements, they can vary significantly in their specific terms. These licenses are generally divided into two main subcategories:
Permissive licenses:
Permissive licenses—such as MIT, BSD, or Apache 2.0—are known for their flexibility and place few constraints on how the source code can be used. Common requirements include
- adding a copy of the license text within the project (often in a licenses.txt file) and
- crediting the original authors, typically in both the source code and any acknowledgments or credits.
Because these obligations are fairly simple to fulfill, permissive licenses have become a popular choice among developers looking for maximum freedom with minimal legal complexity.
Copyleft licenses:
Copyleft licenses tend to pose challenges for proprietary or commercial projects because they contain more restrictive terms. Their most notable drawback is often referred to as the “viral” or “copyleft” effect. This effect mandates that any derivative work — meaning any project incorporating or altering the copylefted code — must be released under the same open source license, which can restrict commercialization. Examples of such licenses include the GNU General Public License (GPL), the GNU Lesser General Public License (LGPL), and the Mozilla Public License (MPL).
Using open source in your projects
Generally, you can safely incorporate code under a permissive license into your project, while software under a copyleft license requires additional caution.
Using tools and not code
Many open source tools — like Blender or GIMP — present minimal risk if you do not embed, alter, or directly include their code in your game. Moreover, outputs generated by these tools, such as images, audio files, or other game assets, can typically be used without worrying about the original license.
However, it’s important to be aware of tools that may inject code automatically. Game engines often do this by adding runtime packages (RTPs) into your project. Always verify the license attached to such injected code. In most situations, these injections follow permissive licenses such as MIT, giving you considerable freedom without imposing strict copyleft obligations.
Separating components
One possible workaround is to isolate the copyleft components instead of fully integrating them. In most standard games, this proves impractical, but it can be viable in situations where a game communicates through a server. Since the server-side code isn’t distributed to end users, you could potentially rely on copyleft software without affecting the client application in those cases.
However, some licenses — such as the MongoDB license — also impose specific restrictions on network usage, so it’s still crucial to review each license’s terms. If you’re unsure, consult your legal team or a trusted attorney to ensure compliance and avoid unintended complications.
Compliance wrap-up
Always maintain a comprehensive record of the open source components you use, along with the corresponding licenses. This documentation is essential both for compliance and for any diligence processes that may arise in future deals or partnerships. In addition:
- Include a licenses.txt file listing all necessary licenses and attributions for the open source tools used.
- Periodically review the open source licenses to remain compliant with any updates or changes.
- Consult a legal professional if you have any doubts about a license’s terms.
By keeping these distinctions in mind and following best practices for compliance, developers can successfully integrate open source software without compromising proprietary work. If you have any further questions or require assistance with open source licenses, don’t hesitate to reach out to us. Happy coding!
