Engines That Power the Gaming Future

The Source Engine and the DOOM 3 Engine - Two Visual Giants

The recent E3 expo in Los Angeles showed us the future of the gaming industry, as well as the novelties we can expect to see in the upcoming months. One of the conclusions was that more and more developers are devoting more attention to achieving realistic (believable) rather than ostentatious graphics. Half-Life 2 was proclaimed to be the best game on display and its Source engine really raised the bar of graphical achievements in games. Another game that attracted a lot of attention in spite of the fact that it is (as is Half-Life 2) still relatively far from completion; I am of course speaking of DOOM 3.

If we disregard the awards and critical acclaim, what we're left with is the essential value of the unfinished games - their technologically advanced engines which allow design teams to create highly realistic in-game worlds. As for the DOOM 3 engine, many things about it are still being kept secret, while the Source engine was first presented at E3. DOOM 3's engine had been written by id Software from scratch, while the Source engine is heavily based on the Havok physics engine (more on that and on the Karma physics engine at the end of the text). It might be interesting to know that the Source engine development started as soon as the original Half-Life hit the stores, five years ago.

Using all accessible info, this piece tries to elaborate the two leading technologies in the visual engine market, and offer a comparative analysis of the two, taking into consideration both capabilities and delivery methods. These two engines have many similarities, but we will try to point out the differences in the approaches to solving various problems. To make things more legible, we will divide the matter in several chapters.

Can unified lighting be the key for horror games?

The scientist looks suspiciously like John Carmack.

Animation

One of the crucial elements concerning visual verisimilitude (What? - Six) is character animation, including facial animation and lip synching. In order to best solve this problem, Valve employed Dr. Paul Ekman from the San Francisco University. Dr. Ekman is an expert in autistic behavior and has spent years researching facial mimics. Dr. Ekman has created a special system that can render up to 40 different facial expressions. Applying this to virtual characters is rather a complex procedure, but thanks to Dr. Ekman's system, the development team had a far easier job (they only picked about 25 expressions for use). The important feature here is that different expressions can be blended. Faces will not only have more polygons; they will consist of different muscle-groups, each of which acts as their natural models. Speech and expressions will activate different muscle-groups which are not directly scripted. This breakthrough in lip-sync technology, along with the new wave-pattern recognition technology, which analyzes the sound wave and automatically renders the lip motion in coherence with what is being said. This will both make lip-synching more realistic and enable characters to have proper lip-synching in many languages. Also the Source engine allows for a character's eyes to be animated as well, and have a far more realistic and somehow wet appearance, all thanks to radiosity calculations and local illumination. A character can now really follow the action, and Valve dealt with this feature with utmost attention to detail.

DOOM 3 characters will mostly be animated using the keyframe interpolation system; a method similar to the one used for rendering CG movies: characters have several key postures, and the computers later fill in the blanks on their own.

Skeletal animation became a 'conditio sine qua non' (Uhm...What? - Six) (It's Latin, you dumbass! It means "I crave Sam's thing." - 2Lions) which keeps getting better and better. The basic idea behind this technique is to create an animated skeleton and then apply a mesh onto it, frame by frame. Every vertex point of the mesh is connected to one of the virtual bones and is animated accordingly. This method both looks more realistic and is faster to render than the old mesh animation method.

Physics model

The physics engine is a very important element which is getting more and more attention as of lately. The Source engine itself is heavily based on the Havok physics engine which has been modified to suit the specific game's needs. The physics engine is responsible for the physical behavior of all characters and items in the in-game world (Heck, Valve even included an anti-grav weapon! - 2Lions). Each object in the game has its own mass which dictates its behavior in accordance with the laws of physics. This advanced physics engine will be capable of solving some pretty complex problems, and in turn, the authentically applied laws of physics will increase the interaction functionality of in-game items... For instance, you will be able to pick up a chair and fight with it, or you may use it to block the door. All this wouldn't be scripted; the physics engine would have to take care of any eventuality, which brings us to "material set", another important novelty in this field. It is actually a method of biding textures, physics characteristics and sound into a class. Each material (metal, wood, glass) has its own material set and is simply applied to a model made of the appropriate material. Material sets will significantly increase the speed of development because they do not require detailed scripting for each single case.

One of the greatest achievements in this segment is the so-called rag-doll physics, most commonly applied in death sequences. If you kill someone at the top of the stairs, he will realistically start falling down them, bumping off all obstacles he may encounter. Rag-doll physics simulates the physics behind the skeletal construction of the model.

We should also mention the friction engine. The best example for this would be that if your character starts walking on a barrel, it will soon start moving in the opposite direction according to the laws of physics. (I can see it now...Online Log Rolling contests.... Ah, technology. - Six)

Definitely not too many polys on this model.

The sheer scale of the "Strider" is incredible.

Rag-doll physics in effect.

DOOM 3 mainly uses its own original physics engine written specifically for this game. One of the main problems it had to address was collision detection. The intersection testing method which keeps testing polygon collision once every n rounds wasn't adequate for high-speed items like bullets. The developers instead, decided to use the object collision detection which is based on models rather than polygons. It calculates collisions, and passes the necessary data on to the main physics engine which simulates the aftermath of the collision. The physics engine functions rather fast, but it is still hard to cope with a multitude of moving objects at once; this is why the programmers developed a separate particle physics system devoted to particle effects only.

Like HL2, DOOM 3 also uses rag-doll physics in order to enhance death sequences. DOOM 3 will also feature the per polygon hit detection, which means that hits will be registered exactly where the bullet went, leaving behind the already outdated hit box method.

Models

Half-Life 2 uses a morphing technology that allows blending a fixed number of basic NPC models into an unlimited variety of NP characters. The highly detailed models in the game will have an average of 5,000 polygons (Gabe Newell's claims sound hardly believable, as high quality models nowadays have up to 3,000). Still, the high level of detail is not so much a result of the increased number of polygons as it is an effect of using advanced shading and reflection technologies. The Source engine supports normal mapping, just like the DOOM3 engine and, using diffused and specular bump mapping, it manages to provide every texture an extreme level of detail and verisimilitude. (You keep using that word. I do not think it means what you think it means. - Six) Yes, it does, Six. Look it up.

This also includes the dynamic skin model, which means that objects will change skins depending on current circumstances (fire burns, bullet holes). This will allow far better damage models in video games.

DOOM 3 uses altogether five texture maps per polygon: local, normal, bump, diffused and specular, which allows models to look way more detailed without increasing the number of polygons to an unmanageable degree. DOOM 3 models are first created in very high quality (up to 800,000 polygons). These models are used for testing purposes in lighting effects, displacements, self-shadowing, etc. The data gathered from the testing process is then projected onto normal models (2,000 - 6,000 polygons). Finally, the model is given the texture structure and skeleton.

Lighting effects

What we already know about DOOM3, definitely says that lighting effects play a major role in creating the in-game atmosphere. DOOM 3 will treat all light-sources equally, regardless of weather they are static or dynamic, thanks to its new unified lightning system. DOOM3 won't use light-maps at all, instead, it will raytrace the light value of each pixel in real-time. This will finally allow the use of real dynamic shadows. If you stand next to a candle, your shadow will flicker on the wall; if you move aside, the shadow will deform...

Apart from this, DOOM3 will probably use the so-called highlights method which gives additional polish to shiny surfaces (i.e. defines points with intense light reflections). Adjusting this object property can create the impression of having an object made of real marble, wood, metal or glass. The only downside to this effect is that it is based on vertexes, so that it looks rather bad on models with fewer polygons.

Lighting effects should be fairly similar in Half-Life2 and DOOM 3, but HL2 will not use the unified lighting model. One thing is for sure - the lighting effects in HL2 will not have the same effect on gameplay as in DOOM 3.

Bump-maps

Even though it is an old technique, I believe bump-mapping is still worth mentioning as an important element that improves the overall visual quality. Bump maps are grayscale bitmaps which, when applied on polygons, make them seem "bumpy". Bump mapping doesn't really deform polygons; it just shades them in a way that they seem deformed. Bump-mapping in combination with dynamic lighting effects provides a substantial increase in visual quality and verisimilitude. (Ha! Verisimilitude! Something that has the appearance of being true or...real.... Okay, you're right. - Six) Thank you. May I continue? (Certainly. - Six)

A good example for bump-mapping in DOOM 3 (which can also be observed in the trailer) are the floor tiles and the highly detailed bricks that can be seen on the walls - if we look carefully at the walls we can actually see the texture patterns that resemble real bricks. Naturally, after intense shoot-outs, you will be able to witness bullet wholes all over the walls and UAC soldiers have wrinkles around their lips (another impressive effect). Bump-mapping was also effectively exploited in Half-life 2 (see the E3 movie) - G-Man's face is a very good example for that, as well as the thoroughly presented objects in the pool room and extensively detailed tiles that were incorporated in almost every outdoor level.

It's hard to believe this is an in-game scene.

And all I ever wanted was someone to hug. So what if I leave pieces of my flesh around?

In short, these would be some of the features of the two best graphic engines on the market. These engines already shifted the boundaries of gaming experience, and as things develop, we are getting closer and closer to diminishing the difference between the real world and the virtual worlds. DOOM3 and Half-Life 2 will certainly help us spend some quality play time until we finally see this dream come true. For what we know, the Source engine has already been licensed for the development of Vampire: The Masquerade - Bloodlines (RPG developed by Troika, published by Activision), and we are sure a modified DOOM 3 engine will soon find itself in a new game (Raven Software's Quake 4 for example. - 2Lions).

Finally, let's take a look at the two most influential physics engines, which are used in most new games either in their original or modified shape.

Havok Physics engine
- latest version 2.0-

Havok physics model (Developed by Havok) is a physics API for all gaming systems, which lets the in-game objects act according to the laws of physics. Some of its main features include rigid body dynamics, deformable object dynamics and vehicle and constrained dynamics. Havok's set of developer tools lets the developers apply physical functionality to different objects environments and characters and design scenes.

Havok's SDK (Software Development Kit) brings several sets of tools:

• Character Kit - helps characters behave naturally in response to the world around them. It contains:
  • the new localized ragdoll effect - it affects certain body parts when they are hit (arm, shoulder). It can also depict the backfiring force when shooting a gun.
  • the classical ragdoll effect - allows believable death sequences, and realistic ways the characters fall. It also provides support for tearing bodies to an unlimited number of pieces.
• Vehicle Kit - allows easy simulation of all possible types of vehicular dynamics. It has special modules for engine characteristics, aerodynamics, control resistance, etc. this kit also allows realistic physics damage models.
• Environmental Dynamics - Havok's rigid body dynamics system represents the physics system behind spectacular particle effects and environment damage models.

The Havok physics engine is currently used by more than sixty development teams some of which are quite famous (Valve Software, Ion Storm, Remedy, Microids, Microsoft Game Studios etc.) for their even more famous games like: Half-Life 2, DeusEx 2, Freelancer, Painkiller, Bulletproof Monk, Mythica, Starsky and Hutch, etc.

Karma Physics engine
-latest version 1.3-

The Karma physics engine is a multi-platform engine, which presents the only true competition to the Havok engine; it features rigid-body dynamics and collision systems, and it has been developed by MathEngine. It is being used in many different game genres.

The Karma rigid-body physics engine gained its popularity thanks to being an integral part of the Unreal engine (since version 829) and it allows realistic simulation of behavior of rigid bodies, and it includes templates for simulating various materials. This engine is capable of supporting huge and complex systems consisting of numerous physically defined blocks that act in accordance with the laws of physics. Items can fall around, break... in other words, react to player behavior. This means that you can influence most things in your environment, which obviously increases interactivity and improves gameplay. It is possible to stack boxes, climb them, hit objects that will realistically react depending on the angle at which you hit them, etc. Still the versatility of the Karma engine doesn't cover things like fluid, rag or smoke animation.

The best known part of the Karma physics engine is the rag-doll model which simulates the skeletal construction of characters, which plays the greatest role in animating death sequences, which is of great importance in some genres.

The Karma engine has been used by SOE, Shiny Entertainment, Ubi Soft, Epic, Lionhead Studios, Paradigm and other in games like: Unreal Tournament 2003; Unreal II: The Awakening; Rainbow Six: Raven Shield; Devastation, Duke Nukem Forever. (It's funny that we should finish this article with a mention of Duke Nukem Forever. - 2Lions)