NextBots represent a significant advancement in NPC (Non-Player Character) technology within the Source engine, first introduced on August 10, 2007. Developed by Valve primarily for "Left 4 Dead," they harness the sophisticated NextBot system to elevate NPC behavior, particularly in terms of pathfinding and navigation. Unlike traditional NPCs, NextBots rely on a navigation mesh (commonly referred to as navmesh), which facilitates their movement and decision-making processes. These navmeshes can either be automatically generated using the "nav_generate" command or manually created with "nav_edit".
More in-depth info on NextBots can be found on the Valve Developer Community.
Example NPC and NextBot Functionality
One example of a NextBot is the "Example NPC," a default inclusion in vanilla games devoid of any modifications. Primarily designed as a pathfinding test, this NextBot assumes the guise of Mossman, uttering the voice cue of Mossman's mo_gowithalyx01 voiceline, saying "I guess you should go with Alyx." before transitioning. Depending on whether or not a map has a navmesh, it may either warn with Female Citizen's watchout voiceline, saying "Watch out!" and dash endlessly in a chosen direction or, if a map has no navmesh, immediately revert to a seated position, repeating the initial voice line.
Utilizing NextBot Bases for Advanced Functionality
To streamline the creation of NextBots and unlock advanced functionalities, developers utilize NextBot bases, addon frameworks tailored for NextBot development. Notable bases like "DrGBase," "R-Base," and "IV04 Base" empower developers with diverse tools and features, enabling the creation of complex NextBots, including those with 3D or 2D representations and specialized functions like execution attacks. However, crafting these advanced NextBots demands a comprehensive understanding of GLua scripting.
Era of Sanic Clones
The emergence of PNG Chasers, colloquially known as "sanic clones," heralds a unique evolution within the NextBot landscape. These entities, often depicted as PNG images or animated GIFs (multi-frame VTF in game), relentlessly pursue players at breakneck speeds, accompanied by cacophonous music. Notable for their remarkable agility, these NextBots possess the ability to leap great heights and obliterate obstacles obstructing their path.
The genesis of PNG Chasers traces back to 2013 with the introduction of the "Sanic Hegehog" addon by "Xyxzen." This creation created a trend wherein users began crafting their versions of PNG Chasers, customizing soundtracks, textures, and performance attributes. Over time, this trend experienced resurgence in mid-2022, leading to the development of more sophisticated iterations like Gargitron and Terminus, which pushed the boundaries of NextBot design and functionality.