The basic plot of Half-Life 2 is pretty simple in concept, much as the first game was. The player is once again Gordon Freeman, but rather than being involved in the action by happenstance, he's placed there by the G-Man. Players of the first game will recall being given a "choice" at the end - work for him, or die horribly. Needless to say, the former was used as the springboard for a sequel.

Gordon was placed in some kind of stasis following the events in Half-Life, and is reactivated by the G-man to deal with a growing problem on Earth - aliens are running the show 1984-style, using Black Mesa's administrator, Dr. Wallace Breen, as a puppet/mouthpiece to control huamnity and maintain order. Gordon is teleported to City 17, an urban center (apparently in Russia, judging by the Cyrillic characters on some of the buildings and the names of some of the local people and places) where Dr. Breen has his main administrative center.

Fortunately, Gordon is not alone against the forces of the alien Combine - characters from Half-Life are working with a resistance movement and will be more than happy to help Gordon, who has become something of a mythical figure amongst the resistance members. Doctors Kleiner and Vance, scientists from Black Mesa, have been working on some high-tech aid for humanity. Barney Calhoun ("the" security guard from Black Mesa) has been working inside "Civil Protection," the oppressive police force of City 17, to keep the reisistance as safe as possible. New characters include Dr. Judith Mossman, an assistant of Eli Vance's, and Eli's daughter Alyx.

Half-Life 2 is comprised of 14 chapters. Since there's a lot to do and see in the game, as well as plenty of stopover areas in some otherwise fast-paced levels, the amount of time it takes to complete each chapter will vary based on the player's proclivity for exploration, perfection, sight-seeing, tomfoolery, hijinx, shenanigans and other sorts of goings-on. A relatively exploratory and skilled player can probably expect to spend 1 to 2 hours in each chapter on average, making for a pretty lengthy game.

Apart from City 17 and its various sub-environs (a canal, a zombie-infested urban wasteland and the streets themselves), game locations include a coastal highway beset by burrowing insect-aliens, labratories, a Combine prison and, of course, the massive Citadel at the center of the city.

The Game

    Requirements
    Minimum:
       Windows(r) 98, 2000, ME, XP
       Pentium/AMD 1.2GHz, 256 MB RAM
       DirectX 7 Compatible Video Card
       Mouse, keyboard
    Preferred:
       Pentium/AMD 2.4GHz
       DirectX 9 Compatible Video Card

The Technology

Materials System

- Instead of traditional textures, Source defines sets of materials that specify what the object is made from and the texture used for that object.  A material specifies how an object will fracture when broken, what it will sound like when broken or dragged across another surface, and what that object’s mass and buoyancy are.  This system is much more flexible than other texture only based systems.
- Materials can interact with objects or NPCs such as mud or ice for vehicles to slide/lose traction on.

Multiplayer Network Code

- Time and gamer tested by millions of gamers around the world
- Support for both LAN based multiplayer and Internet based multiplayer games
- Prediction analysis for interpolating collision/hit detection
- Optimizations for high-latency, high-packet loss 56k connections
 

Advanced Characters

- Detailed and believable characters
- Realistic eyes
     . Focus on player/object, not simply parallel views
     . Proper eye “bulge” for realistic eye reflections
- Simulated musculature provides outstanding emotions, speech and body language
- Language independent speech, characters can naturally speak in many languages
- Skeletal/bone system for animation
- Layered animation system can synthesize complex animations out of several pieces

Physics

- More responsive world with realistic interactions
- Sounds & graphics follow from physics
- AI characters can interact with physically simulated objects
- Ropes/cables, machines, constraint systems, ragdoll physics
- Can be controlled by level design
- Kinematic animated bone followers
- Custom procedural physics controllers
- Vehicles
     . Wheels slip and skid
     . Realistic suspensions with springs on each wheel
     . Realistic leaning during acceleration/deceleration and turning
     . Individually tunable parameters such as horsepower, gearing, max speed, shift speed, tire material, tire friction, spring tension/dampening etc.
     . Multiple players in a vehicle in multiplayer
     . Hovercraft support for cheaper simulation

Advanced AI

- I/O system allowing level designers to control AI
- Sophisticated navigation: characters that run, fly, jump, crouch, climb stairs and ladders, and burrow underground
- AI senses things using sight, sound, smell
- AI relationships determine friend/foe status of other entities
- Battle AI allows squads of AI characters to operate together, know when to advance, retreat, lay cover fire, etc.

 

- 5.1 surround sound, 4 speaker surround
- High-quality 3D specialization
- Custom software DSP
- Automatic DSP based on environmental geometry
- ADPCM decompression
- 16-bit 44KHz, stereo wave data with all features
- MP3 decompression (requires Miles license)
- Support for audio streaming on any wave
- Real-time wave file stitching
- Pre-authored Doppler effect encoded waves
- Pre-authored distance variant encoded waves

UI

- Server browser - Displays all active game servers and allows a player to choose which one to participate on.  Players can filter and sort server lists in order to speed up the display and selection of a server.
- Friends instant messenger - Allows players to message each other both in and out of the game as well as join friends in existing games.  No more confusion about what server your friends are on, you can easily join with this feature.
- VGUI – Valve’s custom GUI interface mimics most of the windows controls but is rendered using the Source engine for both in game and out of game uniform UI display.  VGUI is platform independent and is Unicode compliant for ease of localization


Programming

- All code written in C/C++ using Visual Studio 6.0.  Easily and quickly derive new entities from existing base classes.
- Internal context sensitive performance monitoring system
- Graphics performance measurement tools built into the engine
- Modular code design (via DLL’s) allows swapping out of core components for easy upgrading or code replacement
- Dx9 shaders all written in HLSL


Tools

- Faceposer
    . Facial expression tool used to craft speech and emotions
- Valve Hammer Editor
     . WYSIWYG World editor
     . Create world brushes
     . Terrain editor
     . Place detailed world models and AI NPCs
     . Set navigation points/paths for NPCs
     . Place triggers, clip brushes, logic etc.
     . Allows level designer to hook up I/O between entities to control AI within the game|
- Half-Life Model Viewer
     . Full model previewer
     . Rotate models in any direction
     . Setup hit boxes
     . View physics hull
     . View normals
     . Wireframe, shaded or textured view modes
- Studiomdl
     . Model compiler
- Vbsp, Vrad, Vvis, VMPI
     . Map compilation tools (bsp, lighting and visibility)
     . VMPI – distributed compilation tool allowing level compiles to be spread across many pc’s greatly reducing compile times
- Exporters
     . XSI, Max and Maya .smd exporters for exporting 3D model