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  • A Theory of Compression and Funneling

    - Luke McMillan
  •  [In this article Qantm College game design theory lecturer Luke McMillan here presents a look at how players can be funneled in game design, using the example of classic 2D shooters to illustrate the practice in a work adapted from his PhD at Australia's Queensland Conservatorium of Music.]

    Existing Models of RLD for Environment-Driven Titles

    In terms of rational approaches to contemporary level design, the notion of line of sight being a key difficulty metric is widely used and acknowledged. That is to say, the greater the player's line of sight, the more they will feel empowered and the easier a particular scenario may become. The inverse is also true for limiting player's line of sight; they will feel more hesitant and consequently these types of scenarios are often associated with having a higher degree of difficulty. The confined spaces and use of the flashlight in Doom 3 are an excellent example of these theoretical principles at play. The mood is tense due to the limited line of sight offered by tight, constricted corridors and encounters with enemies are made more difficult due to the limited telegraphing times associated with the limited line of sight.

    The two key metrics behind compression and funneling are portals and occluders. Dependant on the camera position, frustum and perspective, portals will increase the player's line of sight, whilst occluders will limit the player's line of sight. Figure 1, taken from the book Game Level Design by Byrne (2006) demonstrates the concept well from a technical standpoint -- however this is not how the game world is represented for the player.

    Figure 1 [1]

    In the case of nearly all first person and some 3D, third person games, the camera is the avatar or orientated very close behind. Figure 2 is an example of this perspective and is an instance of when the concept of portals and occluders has the most to offer game designers.

    Figure 2

    Not all games though are 3D and in today's market of portable and mobile gaming, the 2D game is commercially viable and popular. With this in mind, let us reconsider the concept of portals and occluders from a traditional, top down 2D perspective. Figure represents the limitations of portals and occluders as the game world is abstracted through the use of an onscreen avatar, which unlike the example in Figure 2, is not limited by occluding elements on screen. In the case of avatar driven 2D games, the portal is the screen itself and the occluder is the physical frame of the screen.

    Figure 3

    It is at this point where the concept of compression and funneling can be used as an alternative to the rational approach of portals and occluders. Compression and funneling is a principle of rational level design which looks at how on screen elements such as enemies, environmental objects , barrages and other collision objects can be used to ramp difficulty and elicit strong emotions in players.

    [1] Occlusion Example. Reprinted from Game Level Design, p 231. Copyright by Charles River Media Inc. Reprinted under the terms of "Fair Dealing" in the Australian Copyright Act, 1968, Section 40.


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