Procedural generation

Procedural generation in video games is the process of creating content through pseudorandom means rather than by hand-crafting the art. Procedural terrain and maps are commonly encountered, but in principle nearly any aspect of the game art can employ procedural generation. Also very commonly generated are quests.

Content can be generated procedurally for inclusion in game media and distributed with the game, but it is also possible for content to be generated on the fly as the player needs it. This can allow seemingly very large data sets to be distributed with a game by making large play areas be distributed as a single random seed.

As it is possible to include the seed with the game, content generated on the fly can be the same for all players. This approach is used in for example Oolite and Pioneer to generate their galaxies.

Legal issues
In some cases the algorithms used may be covered by software patents in jurisdictions which permit algorithms to be patented. The US patent on simplex noise, for example, used to restrict this technology which is used in terrain generation.

It is also possible that the procedure used to generate content may derive it from copyrighted example content in some way. For example if faces are being generated by generative adversarial network (a neural network technique), then the generated faces are commonly described as being someone who "does not exist". In fact the technique is one which particularly tends towards generating derivatives of images already in the training data if over-trained. Hence there are at least some possible cases of media believed to be generated randomly, which might actually be derivative works of (non-Free) copyrighted content. In such cases there can also be legal restrictions on using the likeness of a real person outside of copyright concerns, which vary by jurisdiction.

Sources of pregenerated art
The question whether computer-generated art is even copyrightable in the first place is complex. Nevertheless, at least some online tools generating these provide them with a license suitable for use in Free games.

Artflow.ai issues all of its images under a CC-BY license, which means that presuming the image can't be construed as a derivative work, the portraits it generates are all Free media.

Examples
Procedural maps/levels:
 * Freeciv
 * Nethack

Procedural terrain:
 * Minetest Game

Procedural quests:
 * Oolite

Procedural NPC's:
 * Gearhead