The following is a summarized excerpt from the Interactive Plots & Non-linearity section of "Scriptwriting for Games" from the International Game Developers Association.
Degrees of nonlinearity
Stories could be linear or nonlinear. Nonlinear in the context of storytelling or plot is self-explanatory. In video games this would mean that dialog or cutscenes don't occur in a fixed sequence. Nonlinearity doesn't necessarily mean that the outcome will always be different.
The point is the journey, not the conclusion.
- Parallel Paths (Foldback)
- The game's story elements evolve in a linear sequence
- A linear game could allow the player to explore the game world in a nonlinear fashion, but the plot will still progress via a series of sequential checkpoints
- Linear structures are a reliable and resource-cheap way of approaching the story
- Rarely used and leads to several fatal problems
- The plot begins at a single node and splits at certain points during the game
- This leads to different paths, meaning the number of endings is equal to the number of branching points plus 1 for two-way branching, or more for multi-path branching
- Mistakenly thought to be the only structure of nonlinear stories in games, making the interactive plot seem unsuitable as they'd require vast investment in potentially unused resources
Parallel Paths (Foldback)
- Could also be considered as a fully recombined branching structure
- A tenable and useful approach to story design
- Used in games such as Metal Gear Solid (1998) and Ion Storm's Deus Ex (2000)
- Is a balance between linear and branching structures
- Branches recombine at key points in the story
- Paths need to ensure that the plot will move forward whatever happens. Like: Primary path, secondary path, and a third catch-all path.
- A disadvantage is that more is developed for the game than what is seen. For example with two endings, only players who play the game twice will see all of the story material.
- This disadvantage could be offset by increasing the replayability of the game, by making it short and fun for example.
- The advantage is getting the player more emotionally involved in the game.
- Players are generally expecting not to be given a meaningful choice, because of their prior experience. Thus, the players must be subtly informed that their choices do matter and will affect the game outcome if that is the case.
- The course of the plot does not follow a single path but is comprised of several different paths that develop largely independently
- This is equivalent to the methods employed in quality novels and films to develop the plot, with multiple narrative threads woven together to produce a satisfying story
- It's a powerful and complex way to give a nonlinear story experience
- Highly expressive, and leads to a freedom of movement within the story space which is uncommon
- Used in Perfet Entertainment's Discworld Noir (1999), giving the player a genuine degree of freedom to explore the story space
- There are several problems with this approach that make it of limited future value
- Tracking changes in the plot skeleton during development can be very difficult
- It is very hard to implement structural changes because of the sense of interconnectivity between events
- The complexity of the plot skeleton means that very few members of the development team will fully understand the structure
- The degree of variance in the story structure makes QA much harder to perform completetly
- Most parallel paths are lost on the players if they do not realize the freedom that exists
- In practice, this is no small undertaking