Daniel Brewer explains how Digital Extremes created solid pacing in Warframe

GDC 13: Handling AI in procedural levels

Procedural level creation doesn’t preclude the pacing and flow of more traditional level design, Digital Extremes lead AI programmer Daniel Brewer.

Speaking to attendees of the Game AI developer’s summit at GDC 2013 in San Francisco, Brewer explained how Warframe managed to create compelling gameplay without being able to call on the go-to tools of level designer.

Warframe, described internally as "space ninjas with machine guns", is a 3rd person co-op action shooter that makes use of randomly generated maps.

While the benefits of limitless possibilites in map creation are clear for the player, for the designer there are a number of issues.

If spawn locations aren’t carefully controlled, a mission won’t have the proper pacing to create a compelling experience.

Since sections of the map can appear multiple times in a level, designers can’t simply use these terrain blocks as spawn locations, and scripted sequences would become boring and repetitive.

Digital extremes had to go about crafting the sense of tension another way.

The two primary tools used were the Tac and Influence maps, which provided metrics that act as variables for AI behavior and spawning.

The Tac Map specifically handled the distance on the map to objectives and other locations, while the Influence Map would track player line of sight.

As players move down a hall, their line of sight will move, creating the "influence" variable. If influence is growing, the players are moving towards a location.

Brewer said this was used to make sure enemies always spawned in front of players.

The game keeps track of the number of enemies killed and damage taken by the player, normalized by player level. These metrics are used to calculate a rise in game pace.

As the fight gets more intense, more enemies are spawned to build on the tension. At a certain point, intensity reaches its peak, which is held a bit before the AI eases off the throttle.

This provides a "roller coaster" action experience to that of scripted sequences.

But the mission itself also has to feature into pacing, and for this the developers relied on the Tac Map.

By tracking how far the group was from their objective, the game could slowly increase the number and strength of enemies, meaning that the rise and fall in the action had a larger swell that peaked as the players reached the end of the level.

Procedural level design has plenty to offer: a seemingly limitless supply of content, and as a result less pressure on developers to churn out new maps and missions.

This of course, means new obstacles; "The usual level design tricks won’t work," says Brewer. But intelligent use of metrics to help the AI deal with player behavior can go a long way towards creating the illusion of crafted level design.


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