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  • A Theory of Compression and Funneling

    - Luke McMillan

  • Barrage Compression

    Barrage design is often overlooked nowadays due largely to the fact that pre-determined bullet patterns are largely associated with more nostalgic forms of gaming, namely the Shmup. On a side note though, BulletML is an effective system to learn the nuances of barrage design and the following examples are taken from this particular scripting system.

    Barrages as a form of compression are interesting as they can often be entirely avoided by destroying an enemy before it becomes a problem. This therefore adds a new element of complexity to the RLD of Shmups as players will learn to prioritize the destruction of certain enemies once they learn how problematic a particular enemy barrage type can be, but that is beyond the scope of this particular piece.

    Where we have mainly discussed compression and funneling, barrage design is an effective way of describing the importance of our final metric -- expansion points. As the name suggests, expansion is the opposite to compression from both an emotional and difficulty perspective. Barrages can be described and given difficulty rating, depending on the amount of expansion space offered by them.

    Figure 7

    Figure 7 is an example of a barrage designed for a vertically scrolling game, where the primary axis is facing the top of the screen. In the above example, the barrage has a consistent movement vector and each projectile contained within the larger group has the same velocity. In this particular example, we can see that the expansion opportunities (green arrows) far outnumber the red, compression arrows. This results in a scenario that is easy for the player to navigate.

    Figure 8

    Figure 8 is an example of a harder difficulty metric created by the extremely limited expansion points (green arrows) in comparison to the compressive forces (red arrows). Once again, the barrage uses consistent movement vectors and consistent velocities. The absolute extreme of this can be seen in Danmaku games where barrages have numerous points of origins, creating numerous unique approach vectors. Often this is also compounded by the fact that these barrages will also have different velocities per collision object.

    Based on the information presented so far, we can indentify some very rudimentary difficulty metrics associated with compression and funneling;


    • Lots of obvious expansion points.
    • Limited vectors of compression.
    • Wide funnel points


    • Singular or not obvious expansion points.
    • Compressing along multiple vectors at once, especially those opposite to the primary axis.
    • Narrow funnel points.

    Concluding Thoughts

    Compression and Funneling is a unique way of addressing the design problems associated with 2D level design however it is not a replacement for the line of sight theory -- rather a way of augmenting this already solid model. The application then of compression and funneling to 3D worlds and games is then not too difficult, or dissimilar to what we have been looking at within this piece and is the next logical step in proving the usefulness of this approach. As with anything though, there is always room for improvement. In the case of this piece and applying the theory to 3D world building, the established practices of architectural theory and lighting are obvious points of interest.

    Grof, S. (2002). H.R. Giger and the Soul of the Twentieth Century. In S. Altmeppen (Ed.), Icons; H.R. Giger (pp. 13-21). Zurich: Taschen.


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