Procedural generation

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Procedural generation is a widely used term in the production of media, indicating the possibility to create content on the fly, as opposed to creating it before distribution. This is often related to computer graphics applications and video game level design.

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[edit] Overview

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More generally, the term 'procedural' is strictly related to a procedure used to compute particular functions. This concept takes on dramatic expression in fractals, a specific example of procedural generation; one around which a whole body of mathematics—fractal geometry—has evolved. Most common procedurally generated content include textures and meshes. Sound is seldom procedurally generated in PC applications, the notable exception being speech synthesis. While procedural generation techniques have been employed for years in countless games, few actually used this approach extensively. An exception is Will Wright's Spore, an upcoming video game title populated entirely with procedurally generated content. Some "procedurally generated" elements also appeared in previous games: the first Soldier of Fortune from Raven Software used simple routines to add random detail to enemy models. To a certain degree, it could be said that the lighting in Doom 3 from id Software is "procedurally generated" because it does not rely on lightmaps precomputed using a radiosity process. More recently Avalanche Studios have been using procedural generation to create a large and varied group of tropical islands with high detail in their game Just Cause.

The modern demoscene uses procedural generation for squeezing a lot of impressive audiovisual content into very small executable programs. Farbrausch is a team famous for its achievements in this area, although many similar techniques were already implemented by The Black Lotus in the 1990s.

[edit] Today's applications

Procedurally generated content such as textures and landscapes may exhibit variation, but the generation of a particular item or landscape must be identical from frame to frame. Accordingly, the functions used must be referentially transparent, always returning the same result for the same point, so that they may be called in any order and their results freely cached as necessary. This is similar to lazy evaluation in functional programming languages.

[edit] Video games

The earliest computer games were severely limited by memory constraints. This forced content like maps to be generated algorithmically on the fly: there simply wasn't enough space to store a large amount of pre-made levels and artwork. Pseudorandom number generators were often used with predefined seed values in order to create very large game worlds that appeared premade. For example, The Sentinel supposedly had 10,000 different levels stored in only 48 or 64 kilobytes. An extreme case was Elite, which was originally planned to contain a total of 248 (approximately 282 trillion) galaxies with 256 solar systems each. The publisher, however, was afraid that such a gigantic universe would cause disbelief in players, and eight of these galaxies were chosen for the final version.[1] Other notable early examples include the 1985 game Rescue on Fractalus that used fractal technology to procedurally create in real time the craggy mountains of an alien planet and River Raid, the 1982 Activision game that used a pseudorandom number sequence generated by a linear feedback shift register in order to generate a scrolling maze of obstacles.

Today, most games include thousands of times as much data in terms of memory as algorithmic mechanics. For example, all of the buildings in the large game worlds of the Grand Theft Auto games have been individually designed and placed by artists. In a typical modern video game, game content such as textures and character and environment models are created by artists beforehand, then rendered in the game engine. As the technical capabilities of computers and video game consoles increases, the amount of work required by artists also greatly increases. First, high-end gaming PCs and next-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.

Video game .kkrieger. Using 97,280 bytes of data for one level. Estimated 200–300MB using conventional data storage.
Video game .kkrieger. Using 97,280 bytes of data for one level. Estimated 200–300MB using conventional data storage.

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 (though somewhat less disk access), but with CPUs getting faster, the problem is gradually becoming smaller. However it is not easy to develop such an algorithm for a single tree, let alone for a variety of species (compare Sumac, Birch, Maple and its species), moreover assembling a forest could not be done by just assembling trees because in the real world this introduces interactions between the various trees which dramatically change their appearance (although this is probably a minor detail).

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 are released across several CDs, often exceeding 2 gigabytes in size, more than 20,000 times larger. Naked Sky's RoboBlitz utilized procedural generation to maximize content in a less than 50MB downloadable file for Xbox Live Arcade. Several upcoming commercial titles for the PC, such as Will Wright's Spore, will also make use of procedural synthesis.

[edit] Film

As in video games, procedural generation is often used in film to rapidly create visually interesting and accurate spaces. This comes in a wide variety of applications.

One application is known as an "imperfect factory," where artists can rapidly generate a large number of similar objects. This accounts for the fact that, in real life, no two objects are ever exactly alike. For instance, an artist could model a product for a grocery store shelf, and then create an imperfect factory that would generate a large number of similar objects to populate the shelf.

Noise is extremely important to procedural workflow in film, the most prolific of which is Perlin noise. Noise refers to an algorithm that generates a patterned sequence of pseudorandom numbers.

[edit] Software using procedural generation

  • MaPZone/ProFX – a middleware product designed to create and generate procedural textures in games (used in RoboBlitz).
  • Houdini –is a procedural 3D animation package.
  • Filter Forge – an Adobe Photoshop plugin for designing procedural textures using node-based editing.
  • Art of Illusion – an open source 3D modeler, has an internal node-based procedural texture editor.
  • SpeedTree – a middleware product for procedurally generating trees.
  • Terragen – landscape generation software. Terragen 2 permits procedural generation of an entire world.

[edit] Procedural worlds and universes for space simulations

[edit] Procedural Levels for arcade games

  • The Sentinel (1986) - Used procedural generation to create 10,000 unique levels.
  • Darwinia (2005) - Has procedural landscapes that allowed for greatly reduced game development time.[citation needed]

[edit] Procedural Levels for role-playing games

[edit] Procedural first-person shooters

  • Just Cause (2006) - Game area is over 250,000 acres (1,000 km²), created procedurally[citation needed]
  • RoboBlitz (2006) for XBox360 live arcade and PC (Textures generated on the fly via ProFX)

[edit] Almost entirely procedural games

[edit] Games with Miscellaneous Procedural Effects

[edit] References

  1. ^ Francis Spufford. "Masters of their universe", Guardian, October 18, 2003. 
  2. ^ Ian Bell's Text Elite Page
  3. ^ NVIDIA Water Interaction Demo. NVIDIA (2003). Retrieved on 2007-10-08.

[edit] See also

[edit] External links