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  • Physics in Mass Market Games

    [05.06.08]
    - Calen Henry and Jacob Karsemeyer

  •  Dead Stuff
    Physics has also been used to manage the behavior of characters when they are killed, though early 3D games used animation-based systems instead. Each character model had a specific way it died, no matter how or where it was killed. Once 3D game hardware advanced enough to allow for more complex physics, location-based damage models started to emerge. Soldier of Fortune, for example, uses the GHOUL system, which calculates where a model was shot so that the model reacts with an appropriate animation. If the character is shot in the leg, it grabs its leg; if the character takes a well-aimed shot to the head, its skull explodes. Later versions of the game broke character models into smaller pieces allowing for an even greater variety of dismemberments and cranial detonations.

    Ragdoll physics gave game developers a chance to break away from the static death animations that they had grown accustomed to. With ragdoll physics, once a character dies, its body falls or slumps in a realistic fashion that is unique each time. 2001's Max Payne combined ragdoll physics with Matrix-like slow motion to give players a frame-by-frame view of their enemies' bodies recoiling from bullet fire.

    NaturalMotion's Euphoria is a relatively new technology that combines ragdoll physics with character animations to create a realistic gaming experience. Euphoria "is designed to replace canned animation data in a selective and non-disruptive way, and is capable of creating unique game moments during game play" (NaturalMotion).

    One problem with ragdoll physics is that once a character has been "rag dolled," it must be reset before the player can control it again. In shooting games when players are dying, this works fine; but in football or skateboarding games, it can take away from the experience. In theory, Euphoria will seamlessly blend physics-based interaction with the environment into animation-based movements so characters can stumble and fall, correct their footing, and then continue walking in a realistic manner. The recently released Grand Theft Auto IV is the first game on the market to use the technology.

    Interactivity and Immersive Physical Environments
    In the post-3D years, environmental physics have come to the forefront. The previously rapid pace of graphical advancement has slowed down, while advancements in physics has accelerated.

    Half-Life 2 can all be considered the end result of the graphics boom, as well as the beginning of the interactivity boom. The game was released in 2004 and featured some of the most realistic physics of its time. It focused on interactivity with physical objects, and many of the puzzles in the game revolved around the manipulation of objects while taking into account real world physics such as gravity, weight, magnetism, and buoyancy. The game even gives the player a "gravity gun," which can be used to lift up, propel, and move around objects to see how they behave. By forcing the player to interact with the games physics to solve puzzles and make progress, Half-Life 2 ensured that everyone who plays it has a chance to experience the new generation of game physics.

    Interactive worlds like those in Half-Life 2 are not new. A notable earlier game that advanced interactivity was Jurassic Park: Trespasser (shown), released in 1998. The game was an early attempt on open-world gameplay, but was a dismal failure. Many aspects of the game's engine were too advanced for existing hardware, and aspects of the physics system were too embryonic to function correctly. "There were several notable flaws with Trespasser's solids model as shipped: it ended up only working well when used with roughly cube-shaped boxes with dimensions between 0.5 and 1 meter, it did not model friction well, it was extremely slow, and it was not free of interpenetration even within the size constraints" (Wyckoff).

    Furthermore, the game trod too close to realism, eliminating the player's heads-up display and forcing the player to manipulate game objects with a virtual hand -- using a gun's sight or dialing a phone, for example, all of which were too complex to perform easily with the control system. What the game gained in realistic physics it lost in player engagement. It simply wasn't fun.

    Trespasser was ahead of its time, but too ambitious. More recent open-world games like the Grand Theft Auto series, Oblivion, and Crysis, have succeeded where it failed due to technological progress.

    A recent development in uniform physics models is the ability to have destructible environments. While the concept is not new (it can be traced all the way back to Dig-Dug), current implementations are much more complex. Half-Life 2's advanced object physics do not extend to its environments. Players cannot break through closed doors, and foliage is static and cannot be damaged. These inconsistencies can take away from the immersive experience of playing the game, though in Half-Life 2's case, not enough to warrant any real complaints.

    In contrast, levels in Crysis are much more interactive. Crysis can "[d]ynamically physicallize (using previously defined breaking or shattering characteristics) any arbitrary environmental object or shape, in order to destroy buildings, trees, or other objects, and then further interact with the resulting pieces" (CryENGINE2 Features). Structures and foliage can be destroyed. The leaves of large plants react to the player brushing up against them. This creates a much more cohesive world for the player and does not require the player to acknowledge and ignore indestructible objects that really should be destructible.

    Game physics are becoming more and more developed. As they do, new forms of interactivity are possible, deepening the player's experience and creating richer environments.

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