Proto:Half-Life (Windows)/September 1997 Prototype/Technology Overview

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New Technologies Behind Half-Life

The next step in the evolution of 3D first-person action games, Half-Life combines the most advanced, proprietary technology with genre-breaking gameplay elements.

Improved rendering technologies using 16-bit color

One of the most noticeable limitations of first-person shooters has been their 8 bits per pixel (bpp) color quality. The result is monotonous, unrealistic lighting and color that adds little to the gaming experience. And, even though an accelerator can improve the appearance of 8-bit games, they cannot expand an 8-bit game's color palette beyond the original 256 colors.

Half-Life is engineered in 16-bit color, which expands the available palette to 65,535 colors. And, with support for graphics acceleration, Half-Life lets those with advanced hardware see over 16 million colors. The result is greatly enhanced realism and visual richness. Specifically, 16-bit color makes the following innovations possible:

Realistic lighting, translucency, and blurring Thanks to those 65,535 colors per image, Half-Life engineers can blend light and color in innumerable ways to get a variety of effects. Examples include smoke, metallic surfaces, translucent water and energy beams—even force fields that can fade in and out. Different colored lights from different sources will blend properly as they pool on a floor or wall. And because these features are implemented in software, they can be made an integral part of the gameplay experience, not just a visual treat for those with advanced hardware accelerators.

Dynamically changing surfaces Surfaces in Half-Life are dynamic—they can change over time or as the player interacts with them. Damp walls may grow mossy, water will ripple as the player moves through it, and hard surfaces will retain the scars of a previous firefight.

Non-organic monsters With realistic surfaces, monsters aren't limited to being organic creatures. They can evolve into hybrids of flesh and metal, for example. The realism of the reflections can provide useful feedback to a player, too, such as whether that monster's metal breastplate is made of penetrable aluminum or impermeable steel.

Improved technologies for monsters: skeletal animation

Hand-in-glove with a demand for realistic lighting and color effects is a desire for monsters that look and move as realistically as possible. To accomplish this goal, the engineers at Valve have created a skeletal animation system for monsters. Rather than store a discrete set of polygonal meshes for each key frame of animation, as traditional action games do, the skeletal system moves the "bones" within a monster and deforms a mesh and texture map around them.

There are a number of advantages this gives Half-Life animators as they build more compelling and complex monsters:

Smoother and richer animation Half-Life players will see much smoother animation than in typical action games. While both sprite- and mesh-based animation systems are based on a fixed keyframe animation rate, which is typically targeted at the lowest common denominator system, Half-Life‍ '​s skeletal animation system does not limit the number of frames in an animation. For instance, a typical walk cycle may have as many as 80 frames in Half-Life, as compared to only 4 in some sprite-based games.

6000+ polygon monsters With Valve's new skeletal system, monsters can be much more complex than ever before—without affecting performance. Half-Life will have monsters of up to 6000 polygons, compared to the 500-plygon monsters in traditional mesh-based games..

Anatomically correct motion Through skeletal animation, motion can become more realistic and natural because the animation doesn't depend on thousands of interactions of mesh vertices that are difficult to map in all permutations. The faster a character runs, for instance, the faster the legs will move.

Multiple animations, compound animations and switchable body parts Because skeletal animations are more economical, Half-Life has many different animations per creature. And, rather than have a fixed set of animations that involve a monster's entire body, Valve can build animations of many different parts and then combine them into a whole. Monsters can turn their heads to look at the player while they are running. Troops can pull out weapons and fire while they are moving or kneeling. Compound animations also make it possible to remove or switch body parts in response to the gaming action—say, to allow for a weapons change or to show damage to a monster that's still fighting.

Improved technologies for monsters: artificial intelligence

Valve has created a technology that imbues Half-Life monsters with tactical intelligence, multi-character cooperation, and a supreme will to live. The result is a menagerie of new creatures whose intelligence and unpredictability make them truly formidable adversaries.

Traditionally, game AI is a set of hard-coded if-then decisions for every possible situation that could confront a monster, such as, "If there is a bad guy in this room then shoot at him." Valve took another tack, designing a module-based AI system that provides practically infinite flexibility and monster growth potential. Below are just a few of the ways that AI decision modules work together to produce unprecedented monster intelligence.

Monster behavior based on player's actions moment by moment In Half-Life, monsters might advance only when it makes sense to. They assess how much health the player may have, where the player is heading, how many of their own kind are left in a room, and whether they have enough health themselves to fight. Such conditions and others dictate whether a monster will chase, attack, or retreat. While in other games monsters are basically suicide squads, in Half-Life monsters don't want to die.

Squad (group) behavior Valve's module-based AI technology also adds the new twist of squad behavior and cooperation among monsters. Adversaries can make a threat assessment, recruit others and then plan a coordinated attack against the player.

Flocking behavior Achieving realistic motion for creatures that travel in swarms, flocks, or packs is just as important as achieving it for those that move individually. To do that, Valve has crafted an innovative Flocking Behavior Model that realistically depicts the organic movement of animals such as birds and fish.

Multi-sensory monsters Half-Life monsters possess a rich and varied group of senses for detecting a player's presence—namely, sight, hearing, and smell. For instance, some monsters can't see at all, but locate the player by sound. Others have the ability to track the player who has moved on by using a scent trail. This forces players to rethink their tactics and weapons choices.

Improved technologies for more exciting gameplay

Valve thrusts players into a full-surround gaming environment that is its own thriving space. Half-Life has an ecology and a society. Monsters are breeding, herds are forming, and some monsters prey on others. Players are dropped into the middle of this environment and must learn from what they see. In order to survive, they must use both their weapons and their wits. Some examples of innovations that enhance the player's gameplay experience include:

Continuous-world experience Instead of discrete levels that offer no chance of turning back, Half-Life lets players return to any space they've visited—though what has happened in that space in the player's absence may be surprising

Usable vehicles and props Valve's designers have made sure that vehicles and props aren't merely backdrops to a story—they are tools that must be used to advance in the game. For instance, an underground train system takes players to numerous stations and allows them to backtrack. Some vehicles also contain, or can be used as, weapons to mow down monsters.

Ducking, crouching, and crawling For more realistic and varied action, Half-Life lets players duck and crawl in addition to stand, walk, run, and jump. In addition to expanding players' tactical options, being able to duck and crawl opens up myriad spaces once sealed off to first-person shooters, such as a maze of duct work which can be used to help elude monsters or reach otherwise impossible rooms.

Improved physics In Half-Life, physics and gravity behave more like in the real world than in other. Flooring can be unstable and rickety railings can give way. Even typical tactics for obliterating the enemy must yield to Newtonian physics. For instance, blowing up a soldier who's wearing a backpack of desirable goods also destroys the goods. An initial surprise to experienced gamers, it will challenge players to dream up some interesting alternative solutions.

Scripted sequences to advance the story and interact with Rather than jar players out of their immersion by plugging in backstory details as a voiceover or text screens between levels, Valve's new scripting technology reveals information through sophisticated scripted animations that can be deliberately or accidentally interrupted (such as by shooting at a character or bursting into a scene in progress).

Multi-player games of up to 32 players Half-Life lets up to 32 players to play at once, and it has the the ability to support spectators. Other features include support for game setup, server filtering, and related Internet functionality.

Improvements in sound technology

Sound cues are often a gamer's best reconnaissance and orienting tools, and Valve has made sure that Half-Life's sound technology provides the same quality and feedback reliability as its light, color, and other realism effects.

Real-time DSP Valve has created a proprietary method for producing DSP (digital signal processing) in real time. Without the DSP functions, effects would sound the same in a small hallway as in a wide open space. With DSP, however, a sound effect is muffled underwater, is deadened in a fabric-padded space, and reverberates in a very large room. DSP affects every sound a player makes or hears, such as shots and grunts or machinery and monster noises.

Valve's implementation of the DSP technology also saves disk space and memory. Half-Life can reuse the same effect but give it very different sounds based on the geometry of the room rather than have to record a separate WAV file for each type of effect.

3D sound For any sound they hear, players can tell which direction it is coming from—left, right, below, above, in front, or behind. The source direction changes as they move through the space (e.g., engines that were revving on the left will sound off on the right when a player turns around), and constant sounds recede as players get farther away.

About Valve Software

Founded in 1996, Valve develops games software. It is based in Kirkland, Washington, and consists of more than 20 leading artists, game designers, and programmers. More information about Valve is available through the company's web site at www.valvesoftware.com.

For press inquiries on Half-Life, please contact Eric Twelker at Sierra On-Line, (206) 649-9800 x 5862.