Fractals, noise and agents with applications to landscapes

Abstract

This chapter is about terrains (or landscapes – we will use the words interchange-ably) and noise, two types of content which have more in common than might be expected. We will discuss three very different types of methods for generating such content, but first we will discuss where and why terrains and noise are used, so as to characterise the general case of their content generation problems. Terrains are ubiquitous. Almost any three-dimensional game will feature some ground to stand or drive on, and in most of them there will be some variety such as different types of vegetation, differences in elevation etc. What changes is how much you can interact directly with the terrains, and thus how they affect the game mechanics. At one extreme of the spectrum are flight simulators. In many cases, the terrains has no game-mechanical consequence – you crash if your altitude is zero, but in most cases the minor variations in the terrain are not enough to affect your perfor-mance in the game. Instead, the role of the terrain is to provide a pretty backdrop and help the player to orientate. Key demands on the terrain is therefore that it is visually pleasing and believable, but also that it is huge: airplanes fly fast, are not hemmed in by walls, and can thus cover huge areas. From 30.000 feet one might not be able to see much detail and a low-resolution map might therefore be seen as a solution, but preferably it should be possible to swoop down close to the ground and see hills, houses, creeks and cars. Therefore, a map where the larger features were generated in advances but where details could be generated on demand would be useful. Also, from a high altitude it is easy to see the kind of regularities that re-sults from essentially copying and pasting the same chunks of landscape, so reusing material is not trivial. In open-world games such as Skyrim or the those in the Grand Theft Auto terrains sometimes have mechanical and sometimes aesthetic roles. This poses additional demands on the design. When driving through a landscape in Grand Theft Auto, it 57 58 Noor Shaker, Julian Togelius and Mark J. Nelson needs to believable and visually pleasing, but it also needs to support the stretch of road you are driving on. The mountains in Skyrim look pretty in the distance, but also function as boundaries of traversable space and to break line of sight. To make sure that these demands are satisfied, the generation algorithms need a higher degree of controllability. At the other end of the spectrum are those games where the terrain severely restricts and guides the player's possible course of actions. Here we find first person shooters such as those in the Halo and Call of Duty series. In these cases, terrain generation has more in common with the level generation problems we discussed int the previous chapter. Like terrains, noise is a very common type of game content. Essentially, noise is useful wherever small variations need to be added to a surface (or something that can be seen as a surface). One example of noise is in skyboxes, where cloud cover can be implemented as white noise on blue background. Other examples where noise is used are dust that settles on the ground or walls, certain aspects of water (though water simulation is a complex topic in its own right), fire, plasma, skin and fur coloration etc. You can also see minor topological variations of the ground as noise, which brings us to the similarity between terrains and noise. 4.1.1 Heightmaps and intensity maps