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Procedural generation 116
increases. First, high-end gaming PCs and current-generation game consoles like the Xbox 360 and PlayStation 3 are
capable of rendering scenes containing many very detailed objects with high-resolution textures in high-definition.
This means that artists must invest a great deal more time in creating a single character, vehicle, building, or texture,
since gamers will tend to expect ever-increasingly detailed environments.
Furthermore, the number of unique objects displayed in a video game is increasing. In addition to highly detailed
models, players expect a variety of models that appear substantially different from one another. In older games, a
single character or object model might have been used over and over again throughout a game. With the increased
visual fidelity of modern games, however, it is very jarring (and threatens the suspension of disbelief) to see many
copies of a single object, while the real world contains far more variety. Again, artists would be required to complete
exponentially more work in order to create many different varieties of a particular object. The need to hire larger art
staffs is one of the reasons for the rapid increase in game development costs.
Some initial approaches to procedural synthesis attempted to solve these problems by shifting the burden of content
generation from the artists to programmers who can create code which automatically generates different meshes
according to input parameters. Although sometimes this still happens, what has been recognized is that applying a
purely procedural model is often hard at best, requiring huge amounts of time to evolve into a functional, usable and
realistic-looking method. Instead of writing a procedure that completely builds content procedurally, it has been
proven to be much cheaper and more effective to rely on artist created content for some details. For example,
SpeedTree is middleware used to generate a large variety of trees procedurally, yet its leaf textures can be fetched
from regular files, often representing digitally acquired real foliage. Other effective methods to generate hybrid
content are to procedurally merge different pre-made assets or to procedurally apply some distortions to them.
Supposing, however, a single algorithm can be envisioned to generate a realistic-looking tree, the algorithm could be
called to generate random trees, thus filling a whole forest at runtime, instead of storing all the vertices required by
the various models. This would save storage media space and reduce the burden on artists, while providing a richer
experience. The same method would require far more processing power. Since CPUs are constantly increasing in
speed, however, the latter is becoming less of a hurdle.
A different problem is that it is not easy to develop a good algorithm for a single tree, let alone for a variety of
species (compare Sumac, Birch, Maple). An additional caveat is that assembling a realistic-looking forest could not
be done by simply assembling trees because in the real world there are interactions between the various trees which
can dramatically change their appearance and distribution.
In 2004, a PC first-person shooter called .kkrieger was released that made heavy use of procedural synthesis: while
quite short and very simple, the advanced video effects were packed into just 96 Kilobytes. In contrast, many modern
games have to be released on DVDs, often exceeding 2 gigabytes in size, more than 20,000,000 times larger. Naked
Sky's RoboBlitz used procedural generation to maximize content in a less than 50MB downloadable file for Xbox
Live Arcade. Will Wright's Spore also makes use of procedural synthesis.
In 2008, Valve Software released Left 4 Dead, a first-person shooter based on the Source engine that utilized
procedural generation as a major game mechanic. The game featured a built-in artificial intelligence structure,
dubbed the "Director," which analyzed player statistics and game states on the fly to provide dynamic experiences on
each and every playthrough. Based on different player variables, such as remaining health, ammo, and number of
players, the A.I. Director could potentially create or remove enemies and items so that any given match maintained
an exciting and breakneck pace. Left 4 Dead 2, released in November 2009, expanded on this concept, introducing
even more advanced mechanics to the A.I. Director, such as the ability to generate new paths for players to follow
according to their individual statuses.
An indie game that makes extensive use of procedural generation is Minecraft. In the game the initial state of the
world is mostly random (with guidelines in order to generate Earth-like terrain), and new areas are generated
whenever the player moves towards the edges of the world. This has the benefit that every time a new game is made,
the world is completely different and will need a different method to be successful, adding replay value.