We've reworked this paper and it's been published on Gamecareerguide.com. You can see it here. This version of the essay will remain here, as it is the one we submitted with the thesis project.

Playing Dead: Physics in Pop Games

Jacob Karsemeyer and Calen Henry


          Video game physics have always been an important factor in how enjoyable a game experience is. All of the most memorable video games have found ways of overcoming the constraints of the technology of their time to create experiences that keep players coming back to try to master the nuances of the particular game. When the physics are done wrong it can be disastrous; bargain bins are littered with games that invested more in movie licensing or flashy graphics than they did into tweaking the physics to make the gameplay enjoyable, but when its done right the results are powerful and memorable. To understand the climate of game physics one must first understand the history of pivotal games physics technologies and how they have influenced other game developers as well as current technologies that are in the process of being introduced to the gaming community.

The Golden Era - 1962-1981

          Even before the advanced 3d graphics of current generation video games physics played an important role in the game experience. One of the earliest examples of successful game physics can be found in Spacewar, released in 1962 it is one of the first computer games(spacewar.oversigma.com). In Spacewar players controlled spaceships that fire bullets and missiles at one another while avoiding being shot or colliding with a star. The physics program calculated a gravitational pull that arced the trajectory of bullet fire, and pulled ships towards them. This gave the game a unique feel that even later more technologically advanced games like Asteroids couldn't reproduce.
          A decade later Pong, the first extremely successful video game, brought video games to mainstream audiences. While Pong was primitive as can be, two paddles knock a ball back and forth, it is based on a simple physics calculation that determines where on the paddle the ball hit and bounced it back at the appropriate angle. Atari knew they were onto something good and used the same game mechanic in a single player version, Breakout, where instead of trying to score points on another player, they were trying to destroy stationary bricks by aiming their shots.
          While everyone else was designing games set in abstract and alien worlds a Japanese company was working on a video game with a more human protagonist. Donkey Kong, the first 'Jumping' game, or 'platformer', was released in 1981 (Maria, 193) and garnered a great deal of public attention. Instead of piloting a ship like in Spacewar, or a floating paddle like in Pong, Donkey Kong players would control a carpenter named Jumpman. Physics were still very primitive at this time, Jumpman climbed ladders and hopped over barrels, but they were applied in an effective and inviting way that kept players coming back. To this day Donkey Kong has one of the most competitive player communities, as can be seen in “The King of Kong: A Fistful of Quarters”. The same jumping mechanic was used in a series of follow-ups that Nintendo released to capitalize on its popularity.
          Donkey Kong was a huge success and Nintendo knew they were onto something. They used the money they had earned from their series of successful arcade machines and created a video game console intended for home use dubbed the Nintendo Entertainment System (NES) in North America and the Family Computer (Famicom) in Japan. Super Mario Brothers (SMB), the game that was shipped with the system, featured a familiar character, Jumpman, only now he was called Mario and was a plumber instead of a carpenter. SMB used friction and momentum to give the game a more realistic feel. Mario could jump further if he was running quicker and slowly slid to a halt depending on how quickly he was running. Using software to emulate real world physics made the game intuitive and even players who had never played a video game before found it enjoyable. Thesebasic additions to the jump and dodge mechanic brought platforming to a new level and was used in countless other subsequent video games and soon everyone from Mario’s competition, Sonic, to the Ninja Turtles was slipping and sliding around with realistic momentum. Super Mario Brothers went on to be far more successful than any of the previous Nintendo games and has sold more copies than any other Mario game (gamecubicle.com). 

2.5D – 1990 - 96

          While some game designers were just starting to understand how to manipulate gaming software to allow for enjoyable physics in 2 dimensional games, a different group was working on something entirely different; ways to display 3 dimensional images. 2.5d is a term used to represent some of the early attempts to use software tricks to create the illusion of 3 dimensions. When game designers made the jump from 2D to 2.5d they compromised a lot of the progress they had made in refining gameplay experiences through physics. The first computer games to attempt to mimic 3d used a process called ray-tracing to draw lines between the floor and roof based on the inputted coordinates that would then be skewed to simulate depth. Games like 3D Monster Maze used this method to achieve early 3D graphics on a PC, but none of them achieved mainstream success.
          Since the video games consoles of that time didn’t have to computer power necessary to perform raytracing, Nintendo started development on some games using a technology calledMode 7. Mode 7 mapped 2 dimensional textures into a 3d space by rotating them so that the player moved across them instead of along them. These games were still essentially 2 dimensional, but width was mapped across depth to give the illusion of 3 dimensions.When Teenage Mutant Ninja Turtles: Turtles in Time was ported from Arcade to the SNES an entire level “was changed from a regular side-scrolling view in the arcade to a Mode 7 view in the SNES port”(wikipedia.com) so that the players moved ‘into’ the screen rather than across it.
            As 3d games progressed the rapidly advancing technology of the PC became a more attractive medium for designers looking to push as many pixels as possible. While the first 3d computer games like 3d Monster maze preceded it by over a decade, it was Wolfenstein that really brought 3d graphics into the mainstream. Wolfenstein was a First Person Shooter (FPS) meaning that the player saw through the eyes of the character they were controlling. While Wolfenstein breakthrough game that really propelled the FPS genre, the in game physics were still very primitive. The developers of Wolfenstein, Id Software, used a slightly more advanced version of ray tracing, called ray casting, that was capable of scaling characters to simulate depth, and drawing textures onto objects. Both ray tracing and ray casting are algorithms used to render 3d scenes on 2d screens. Ray casting is much faster. Games like Doom and Duke Nukem, further refined the 2.5d, or pseudo-3d technology to allow more creative control, but it wasn’t until Id Software revealed Quake that the gaming community really got a chance to experience true 3d gaming.

The Wonderful World of 3d 1996-present day

          Quake was released in 1996 by Id software and was the first successful true 3d game. The characters and levels were made up of 3d models instead of 2d sprites, which was quite revolutionary for its time and allowed for physics to be effectively applied to true 3d space. Explosions pushed objects and players back, they ran and jumped in a more immersive and realistic way, and when directly hit with a rocket enemies would explode into giblets (shortened to gibs by the gaming community) of flesh. These new physics not only made gameplay more realistic and immersive, but also created potential for players to experiment in ways that the designers had not expected. Rocket Jumping was a tactic that emerged where a player jumped and fired a rocket straight down so that the explosion would propel them further into the air. This allowed players to use the unexpected results of physics to move through the levels in ways that the designers had not intended. It was quickly realized that giving the player some simple physics based mechanics allowed to the experiment with the game and experience it in ways that had not been possible before.
          In the 32 bit console era of Sega Saturn and Sony Playstation many 2d game developers unsuccessfully attempted to bring their games into 3d but it was a title that featured everyone’s favorite plumber, Mario, that successfully brought 3d gaming to consoles. In Mario 64 all of the physics that made Mario popular in his beloved 2d franchise were transferred into 3d. He jumped, slid, and bounced through 3 dimensions just as smoothly as he ever had, and set a high bar for other games that were trying to make the jump from 2d to 3d. Nintendo was clearly adept at rendering physics in ways that made their games engaging. The recently released Super Mario Galaxy is a testament to their ability to continue pushing the envelope in that regard. Super Mario Galaxy features globe shaped levels that have gravitational pull so that Mario can run along the underside of the globe and not fall off. By manipulating this mechanic in every way possible, Nintendo has again given other game developers a lesson in how to use physics to create successful games.

Realism VS Arcade

          Once game developers started to get more comfortable with developing games in 3d, two distinct streams of gameplay emerged; Arcade and Simulation. In arcade games the physics were used less to create realistic situations and more to enhance gameplay; arcade style games are often marked by outrageous and spectacular acrobatics executed at the push of a button. Simulation games go the other route and use physics as realistically as possible, leading to unforgiving, but rewarding gameplay experiences. These distinctions are most obvious in sports games. In racing games ultimate realism is represented by Gran Turismo, which is popular amongst gamers and car enthusiasts alike. Never before had a game so accurately capture the experience of driving; each of the games 150 licensed automobiles felt unique and true to the real world car they emulated. Gran Turismo was able to ‘mimic the physics of their real-life counterparts’ (gamecritics.com) Minor modifications to the car would have noticeable results that left car enthusiasts ecstatic, and casual gamers bewildered. On the other side of the spectrum games like Cruis’n USA and Burnout Revenge had players smashing through other cars as though they were empty garbage bins. These Arcade style games are much more fast paced, with cars using nitrous oxide to travel at airplane like speeds. Large jumps that would destroy any real world car instead provide bonus points or Nitrous refills. In these games physics are used to create more stimulating experiences, rather than more realistic ones. The recent Xbox 360 game Burnout Paradise features some of the most technically advanced and fantastical bumper rumpling car crash physics seen in a game, cars wrap around poles and crumple like an according when they collide with a wall. The ways in which the physics are implemented in a game determine what style of gameplay the final product will have and whether it’s a true to life simulation, or a fantastical arcade experience.

Dead Stuff

          Physics has also been used in dealing with how characters behave once they have been killed. Early 3d games used animation based systems when characters died. This meant that meant that each character model had a specific way that they died, no matter how or where they were shot. Once 3d gaming hardware started to advance and allow for more complex physics, location based damage models started to emerge. The developers of Soldier of Fortune used the GHOUL system which calculated where a model was shot so that the model could react with the appropriate animation; they would grab their leg as they fell if it had been shot or their head would explode with a well aimed headshot. Later versions of the game broke character models into even smaller pieces allowing for an even greater variety of dismemberments and cranial detonations.
          Ragdoll physics allowed game designers to break away from the static death animations that they had grown accustomed to. Once a character died their body would fall or slump in a realistic fashion that was unique each time. 2001’s Max Payne combined ragdoll physics with Matrix-like slow motion to give players a frame-by-frame view of the bodies of their enemies recoiling from bullet fire. Euphoria is a 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.” (Natural Motion).One problem with ragdoll physics is that once a character has been rag dolled the character model must be reset before the player can control them again. In shooting games when players are dying this works fine, but in football or skateboarding games, it can take away from the experience. Euphoria will seamlessly blend physics based interaction with the environment into animation based movements so that characters can stumble and fall, correct their footing, and then continue walking in a realistic manner. There are not any games available that use this technology, but the upcoming Grand Theft Auto will be using Euphoria to give an unseen level of realism to the character animations.

Interactivity and Immersive Physical Environments

            In the post 3d video game environmental Physics have come to the forefront. The previous rapid pace of graphical advancement has slowed down, and game physics advancement has accelerated. Realistic physical interaction with the game world has started to emerge. Half-Life 2 can all be considered to be the end result of the graphics boom as well as the beginning of the interactivity boom.
Half-Life 2 was released in 2004 and featured some of the most realistic physics at the 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 like gravity, weight, magnetism and buoyancy. The developers even went as far as giving the player a ‘Gravity Gun’ to allow them to lift up, propel and move around objects to see how they behaved. By forcing the player to interact with the games physics to solve puzzles and make progress, Half-Life 2 ensured that everyone who played it got 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 interactivitywas the Jurassic Park game “Trespasser” released in 1998. The game was an early attempt open world gameplay, but was a dismal failure. Many aspects of the games 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”, having no player HUD and forcing the player to manipulate most game objects with a virtual hand. These included activities such as using a gun’s sights, or dialing a phone, all of which were too complex to easily perform with the control system. What the game gained in realistic physics it lost in player engagement; it just was not fun. Trespasser was ahead of its time, but too ambitious. More recent open world games like the Grand Theft Auto series, Oblivion and most recently Crysis have, because of technological progress, succeeded where it failed. 
            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.  In contrast to Half-Life 2, levels in the recent Crysis are much more interactive. Crysis can “Dynamically 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 and the leaves of large plants will 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.
            As video games advance the physics are becoming more and more developed. One can see through the progression of 3d games like Trespasser, Half-Life 2 and Crysis that as physics advance new forms of interactivity are possible, deepening the players experience and creating richer game environments.

Physics Engines

            To execute realistic physics in 3d games developers have to devote a portion of the game engine to rendering physical interaction. This is done in one of two ways, writing a physics engine for the game or using an existing middleware physics engine. Both approaches are common, but the use of a third party physics engine is becoming increasingly common. Half-Life 2 and Crysis use proprietary physics engines, but Half-Life 2 used Havok as a basis. Havok Physics, the leading middleware engine, is currently on its fifth Iteration. Havok uses a dynamical simulation model to simulate “systems of objects that are free to move, usually in three dimensions according to Newton's laws of dynamics, or approximations thereto.” (Wikipedia) Because Havok deals with all the game physics, it leaves the designers more time to work on other aspects of the game. The Havok engine is also frequently updated allowing developers access to state of the art physics, without developing them in house. Since Havok is designed as middleware it is easy for developers to implement. Another physics engine provider is Ageia, who has recently been bought by nVidia. Ageia’s software works with a physics accelerator, a hardware product required to take advantage of their engine.  While consumers haven’t been very receptive of the additional piece of hardware, many game designers have implemented Ageia physics as an optional feature in their game. The upcoming Lucasarts game Star Wars: The Force Unleashed uses three separate, third party physics engines. It uses Havok for rigid body physics (objects in the levels), Digital Molecular Modeling (DMM) for material physics and Euphoria for character interaction with the world. DMM is a system that allows materials in the game (glass, wood, metal, etc.) to be assigned realistic properties. This information is fed into Havok to determine interaction with the rest of the environment. DMM is proprietary to Lucasarts until September 2008 (lucasarts.com). As games like Force Unleashed that use highly dynamic physics models are released character animation will likely need to change to accommodate the entropy introduced when an individual plays the game. Increasingly complex physics will call for increasingly complex, reactionary behavior in all aspects of game, and the integration of multiple control engines in single games may well become commonplace.
            As gaming technology advances, physics will become more and more important to gamers who are looking to make the best of their hardware. They can be tweaked to create unforgettable gameplay experiences, as Nintendo has grown proficient at doing, or can end up getting in the way of the game experience, as was the case with Jurassic Park: Trespasser. New technologies like Euphoria will ensure that realistic physics are available to any developer willing to foot the bill.Hopefully this means that they can spend more time refining other gameplay elements to ensure an enjoyable overall experience.

Bibiolography

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