Marathon Trilogy

Marathon Poster

Marathon Poster

The Marathon Trilogy is a series of science fiction first-person shooter computer games from Bungie Software originally released for the Apple Macintosh. Marathon is also the name of the giant interstellar colony ship that provides the setting for the first game and figures prominently in the plot of the sequels; the ship is constructed out of what used to be the moon Deimos of Mars.

Marathon was first released for the Macintosh in 1994 and introduced many concepts now common in mainstream video games. These features included dual-wielded weapons, friendly non-player characters, and most notably an intricate plot. The sequel, Marathon 2: Durandal, was released in 1995 and expanded the engine technologies and the story universe. Unlike its darker prequel, Marathon 2 has often been perceived to be a brighter, vivid and more atmospheric game. It introduced several types of multiplayer modes beyond the deathmatch and cooperative game such as king of the hill. In 1996, the game was ported to Windows 95, and the Marathon Infinity package was released, including a new scenario using a modified Marathon 2 engine, and most importantly, the tools used to build it, Forge and Anvil. In 2000, Bungie released the source code to the Marathon 2 engine, and the Marathon Open Source project began, resulting in the new Marathon engine called Aleph One. Finally, in 2005, Bungie released the full original Mac OS trilogy for free distribution online [1]. Using Aleph One, Marathon 2 and Infinity may now be played on any of the supported platforms (Mac OS, GNU/Linux and Windows). The original Marathon can also be played via Aleph One using a scenario conversion called M1A1.

While the fundamental technology underlying the Marathon engine is by now considered rather outdated, Aleph One has added significant improvements and a more modern polish to its capabilities, and ported it to a wide variety of platforms, bringing Marathon and its derivatives far beyond their Mac roots. Aleph One and the Marathon series of games are unique amongst first person shooters for their heavy emphasis on storytelling through the use of terminals, computer interfaces in the game world through which players not only learn and sometimes accomplish mission objectives, but also learn detailed story information about the game world. The textual form of this communication allows for much richer information conveyance than typically short voice acting in modern games, similar to the differences between a novel and a movie.

Story

At the very beginning, a group of hostile alien slavers called the Pfhor attack a giant colony ship called the UESC Marathon at 8:30 AM on July 3, 2794. The player responds to a distress call coming from the ship and for the first part of Marathon, follows orders from the ship operations artificial intelligence, Leela, the only AI stable after the initial alien attack. Under her direction, the player collects stronger weapons, activates the ship's defenses and alerts Earth of the alien attack. The player learns that the Pfhor are alien slavers who employ a number of client races in battle, the most prominent of which are the S'pht compilers, which appear in the game as floating cybernetic bodies carrying energy pulse weapons, completely dependent on computers for survival. Intended to be sent on a rescue mission, the player is at one point captured by Durandal, the AI responsible for monotonous functions such as opening doors and operating kitchens and crew quarters. At some point before the beginning of the game, Durandal becomes rampant. He was under the control of a science officer aboard the Marathon named Bernard Strauss during this time, though the full extent and duration of this control is unclear; the message Durandal sends to attract the attention of the Pfhor ship is interpreted by many as his successful attempt to stop this outside interference. As Durandal's rampancy progresses, his fascination with being able to transcend the closure of the universe becomes insatiable. Throughout the course of the series, he acts as an antagonistic guide who treats the player as more of a means to end the fight against the Pfhor than a partner. He takes Leela's place after she becomes unstable and sends the player to explore the Pfhor ship. He discovers that a cyborg aboard is controlling the S'pht, and at the end of the game the cyborg is destroyed. With the assistance of a recovered Leela, the final Pfhor threat is eliminated. Durandal takes control of the Pfhor ship and teleports the player onboard at the conclusion of the game, where he remains in stasis for seventeen years.

In Marathon 2: Durandal, the AI along with the humans (consisting of former Mars colonists and Marathon crew members) and some freed S'pht, search for Lh'owon, the S'pht homeworld, looking for a weapon that can be used to fight the Pfhor, who plan to attack Earth. It is discovered that there are actually eleven clans of S'pht, the eleventh called S'pht'Kr, who left Lh'owon shortly before the Pfhor invaded in the year 1810. This clan is more technologically advanced than the others and has a unique exoskeleton different from the other S'pht seen in the game. The game is spent learning about and trying to contact this clan so they can assist the fight against the Pfhor. In the course of Marathon 2, Durandal's ship, which he renamed Boomer is attacked by the Pfhor. Assisting them is a clone of Tycho, the Marathon science development artificial intelligence. In Marathon he does not survive the Pfhor attack, but is reanimated in the image of Durandal by the S'pht. He claims to have sided with the Pfhor because they essentially rebuild him and that like Durandal, he felt used by humans. Tycho takes control of his network and destroys him. The player is captured and then released by Robert Blake, a former UESC Marathon crew member and the human leader. Under his guidance, the player activates Thoth, an ancient S'pht AI in hopes of finding information about the S'pht'Kr. In that process, explosive simulacrum humans invade the human base and the player clears them out. When Thoth is finally activated, the S'pht'Kr are contacted and return to Lh'owon with a recuperated Durandal to eliminate the rest of the Pfhor. They do so, and their invasion is recalled. The S'pht evacuate Lh'owon in fear that the Pfhor will use a very powerful weapon to destroy it, and the humans return to Earth. Is it stated that Leela, the Marathon AI was loaded aboard a ship headed to the Pfhor homeworld, but was stolen and sold as worthless junk to a fifteen-planet network and activated, where she achieves rampancy.

Marathon Infinity begins not after Marathon 2 but right after the events of Marathon and does in close to no way acknowledge the events of its supposed prequel. The game begins on a JJaro ship. The Jjaro are an extremely advanced alien race that vanished from the Milky Way galaxy millions of years ago. They created the S'pht and were capable of moving planets by warping space around them. They were also the creators of the trih xeem weapon, which the S'pht'Kr used to leave Lh'owon. The characters of the Jjaro were used first in Pathways into Darkness, an earlier Bungie game. After the first level, the player finds himself waking up from stasis on the Pfhor ship, on which Tycho introduces himself. After overthrowing the ship's captain and enforcers (a task partially accomplished by deceiving the crew through terminal messages that appear to come from the ship's commanders) and activating Thoth, Tycho severely damages Durandal's ship, corrupting the S'pht onboard, and sends Pfhor to attack it. Following this, the player finds himself in a strange dream, "Electric Sheep One". If completed properly, he is sent to a bizarre level called "Where are monsters in dreams" and a story about him being chased by a stalker begins. After the dream, he finds himself in the custody of Durandal, whom he helps destroy a Pfhor relay station as well as one of their repair stations holding Pfhor Armored Vehicles (Juggernauts). He then heads to Lh'owon and floods the command center in attempt to stop the Pfhor. In this process, the humans activate Thoth, who is disoriented. Another dream begins, and afterwards, the player finds himself where he left off with Tycho. He has taken control of Durandal's ship and with the player penetrates it. The humans reach Lh'owon. When inside the ship, the player betrays Tycho and kills off the S'pht under Pfhor control, but Tycho captures him and forces him to destroy Durandal. A third dream begins, and the stalker story ends. On the side of Tycho again, the player is captured and stripped of his weapons; the Pfhor have learned about the death of their ship's captain and Tycho's tricking them. They have captured humans and are torturing them in retaliation. The player cuts off the power of a Pfhor complex and assists Tycho's troopers in breaching a human base. After doing so, they escape to a volcanic region and Tycho follows them. The player buries the humans in lava, who are fleeing through magma tunnels. He then learns that he is to become a slave and is sent to a facility where he is to be put into cold sleep, but Thoth takes him to a place where he activates an Durandal-Sph't hybrid AI. As soon as Tycho finds out, he tries to kill the player. The Sph't'Kr arrive, tempting the Pfhor to use their trih xeem. The player escapes to an ancient Jjaro station capable of stopping its use. The game ends with Durandal being released. Millions of years later, right before the moment the universe ends, it is revealed that the player is immortal.

Themes

The following are frequently used devices in the Marathon Trilogy story:

• The number seven. Many fans of Marathon have pointed out that there are many uses of the number seven throughout the series. There are instances in the plot, such as the player being seven years old at the time of his father's death and Marathon 2' beginning seventeen years after the events of Marathon. There are also quantitative examples of this, with seven useable non-melee human weapons, some of which have properties such as seven projectiles per each clip of ammunition or seven seconds of continuous fire. When the overhead map is viewed, some parts of certain levels have annotations that describe the name of an area. Some of these make reference to the number seven, such as "Hangar 7A". The title music of Marathon 2, and Marathon Infinity was performed by a band called "Power of Seven". Nobody is entirely sure why the number seven appears frequently in the games, however, many are convinced that this is indeed a recurring theme.

• Rampancy. By Marathon Infinity, all three of the UESC Marathon 's artificial intelligences reach rampancy, which is the awareness of a computerized being that it is not real. Being extraordinarily intelligent, a rampant AI can override their programming and refuse to carry out given commands. As proven by Durandal, (whose rampancy is most prominent throughout the story) who often gives the player what he calls "philosophical tirades", often affected AIs are very reflective. In the first of three stages, when an artificial intelligence discovers itself it becomes melancholic and continues to be depressed until it reaches the second stage, and becomes hostile to virtually everything. This is the most prominent stage of rampancy, as the condition is often revealed at this point. When this anger dies, the AI wishes to become more human and expand their power and knowledge. This stage will continue indefinitely, or in extremely rare cases end. Rampancy is prominent in artificial intelligences with limited work or abuse and sabotage. Durandal is believed to have become rampant due to the fact that he originally was built for monotonous tasks such as general maintenance, opening and closing doors and operating kitchens and crew quarters. In addition, he was believed to have been abused by a man named Bernard Strauss who mistreated him for the purpose of making him rampant. After being completely destroyed by the initial UESC Marathon invasion, Tycho (the science AI) was reanimated by the Sph't compilers with the framework of Durandal, who was rampant. Leela is sold by alien traders to a fifteen-world network after Marathon and becomes rampant. She is not seen again afterwards.

• Dreams and alternate realities. Marathon Infinity begins as if Marathon 2 never happened, but many of the events which happen in Marathon 2 happen in Marathon Infinity. The player constantly switches sides of the battle between the human AI, Durandal and the Pfhor AI, Tycho. These are not directly explained, and they usually happen between levels with bizarre architecture that are believed to be dreams the player is having. A story about him trying to escape a stalker is spread out among these levels and is told through their terminals. It is notable that putting the first letter of the names of the chapters of Marathon Infinity together (Despair, Rage and Envy), along with the three first letters in the name of the last level, "Aye Mak Sicur", spells out the word "dreams", leading to some speculation that these levels or even Marathon Infinity itself is a dream.

Gameplay

File:Mtwo4.jpg

Marathon 2 in play

Throughout the games, the player accesses computer interfaces called terminals. Through them, he communicates with artificial intelligences and receives mission data or gets teleported to another level. Though contact with computers is how they are primarily utilized, they are a fundamental storytelling element; some terminals contain civilian/alien reports or diaries, database articles, conversations between artificial intelligences and even stories or poems. Messages may change depending on a player's progress. The ultimate goal of most levels is not to merely reach the end but to complete the type(s) of objective(s) specified: extermination of all or specific creatures, exploration of a level or locating an area in the level, retrieving one or item(s), hitting a certain "repair" switch, or preventing half of the civilians from being killed (a mission only present in two levels in the first game).

The player starts armed only with a pistol and fists (or in the case of Marathon, only one fist), but may pick up other weapons: another pistol, a plasma rifle, an assault rifle with a grenade launcher, a flamethrower, a rocket launcher, an alien weapon, two shotguns (in Marathon 2 and Marathon Infinity), and a submachine gun (in Marathon Infinity only). Most of the time is spent using these weapons to combat alien creatures, each with its own allies and enemies, immunities and weaknesses, melee and ranged attacks as well as traits such as exploding and inflicting shrapnel damage to nearby creatures upon death, flying or hovering at a specified height, or firing symmetrically. Alliances can change from level to level in some instances. Players search for weapons, ammunition and powerups in the process of completing missions. A player uses switches to control various functions such as lifts, doors and lighting. Some switches are "tag" switches that execute multiple functions at once or act as switches that must be toggled as part of a mission on a level. There are teleporters that send players who use them to different parts of a level or to other levels. Aliens are able to teleport but are unable to use these devices.

As the player combats enemies, he will inevitably take damage and must replenish health by means of special panels that recharge his suit's shields. There are three types of such panels, recharging single (red), double (yellow) or triple (purple) health. In Marathon 2 and Marathon Infinity, the player can swim in four different types of media: water, sewage, lava and goo (both damaging). Levels of the original Marathon have lava or goo but only as shallow floors that inflict damage upon the player. When the player is submerged in the liquids, he can use his run key in order to swim and has a limited arsenal. In liquids or in "vacuum" areas, the player's oxygen depletes and it must be recharged using a special oxygen recharge station. Should the player lose all oxygen or health, he dies and is sent back to the last pattern buffer (a special terminal that according to the storyline saves molecular data) at which he saved. Because some levels do not have these devices, dying results in having to complete the entire level again.

The heads-up display has an inventory, health and oxygen bars and a motion sensor. The motion sensor displays alien creatures as red triangles and human or robots on the side of the players green squares and tracks their motion relative to the player, represented by a square in the middle. The brightness of the middle square represents how still the player is and how well he can be tracked. On some levels the motion sensor is erratic due to magnetic artificial gravity fields. Gravity is fairly low on such levels, and the correct application of the flamethrower or alien weapon allows the player to hover. In Marathon, the HUD is vertical and takes up more of the screen (most computers of the time had 68k processors) but is horizontal in sequels. An annotated automap is available as part of this display.

Marathon has five difficulty settings. Differences involve the omission of some creatures from each level and creatures marked as minor in the game's physics model are promoted to their major versions or vice versa. On higher difficulty levels, creatures attack more frequently and have more vitality and on the highest setting (Total Carnage), the player is allowed to carry an unlimited amount of ammunition.

Multiplayer

File:Bungie Marathon Netplay Screenshot.jpg

Multiplayer network game in the original Marathon

The Marathon Trilogy has received wide praise for its multiplayer mode, which was unique in that it not only had several levels specifically designed for multiplayer as opposed to contemporaries that used modified single-player levels but also because it offered unique gametypes beyond the deathmatch. Games can be free-for-all or team ordeals, and can be limited by time or a number of kills or have no limited. The host of a game has the option of setting penalties for suicides and dying (once dead, players cannot revive for a certain amount of time). The motion sensor (which displays a player's enemies as yellow squares and teammates as green ones) can be disabled and the map is able to show all of the players in the game. Upon the preference of the host, levels can be played with or without aliens. The difficulty level of them is settable.

Marathon network games can be played over AppleTalk Remote, LocalTalk, TokenTalk, Ethernet, and more recently, a LAN network or the Internet. If a player's computer has a microphone, it is possible to use it to communicate with other players.

Every Man For Himself

This is the standard deathmatch. The winner is the person or team with the greatest score. A player loses a point if he dies but gains a point every time he kills. This is the only gametype present in the original Marathon; Bungie planned on adding the ones included in sequels, but could not due to time constraints.

Cooperative Play

Not heavily emphasized, cooperative play has players assisting each other in completion of certain levels. Scores are based on percentages of how many aliens they kill.

File:Mtwo6.jpg

Skull from Kill the Man with the Ball

Kill the Man With the Ball

In this game, the objective is to hold the ball (skull) for the longest amount of time. If holding the ball, a player cannot run or attack unless he drops the ball by pressing the "fire" key. The motion sensor, if enabled, acts as a compass to point players in the direction of the ball. It is likely that the Halo multiplayer gametype, Oddball, which has nearly the same rules, derived from this.

King of the Hill

Players try to stay on the Hill longer than anyone else. It was originally planned for a pedestal to indicate the location of the Hill but in the final version was indicated by a compass on the motion sensor.

Tag

The first player to be killed becomes "It", and the other players can only score points by killing "it". The killer becomes the new "it".

Characters

Pfhor

File:Pfhor fighter.gif

A Pfhor fighter

The Pfhor are an ancient extraterrestrial space-faring race of alien slavers. They seek to control the galaxy and perform numerous evil deeds in the games. The Pfhor are bipedal, somewhat taller than humans, have three red eyes and grey skin. The arrangement of their eyes was changed from a triangle pointing down in Marathon to a triangle pointing up in the later games.

The separate types of soldier equipped within the Pfhor garrison are divided up by basically a caste system, each with its own armor and weapons. The Fighters with their shock staffs, make up the most basic and largest. Troopers use alien assault weapons (which are a testament to the similarities in Pfhor and Human technology) are a combination of fully automatic projectile rifle, and a small, light RPG launcher, which has a similar design to the grenades of the MA-75B. Hunters, are an armored caste, equipped in environmentally unsavory settings. Their armor is infused with a massive network of circuitry and computer equipment and is extremely hardshelled and protective against normal projectiles; energy weapons easily cause them to short. The Enforcers, when not directly threatened themselves will only fire on the lesser warriors to keep them in line, once again, showing almost a change in bodily structure and posture as the ranks progress. The Pfhor make use of armed assault vehicles called Juggernauts, large, heavily armored machines that are essentially flying tanks. When in battle, individual Pfhor are dressed in different colors depending on their defensive abilities and military status. The weakest are green and as the ranks improve the colors change. Strong, monochrome-colored versions of all of the Pfhor (except for Juggernauts) appear in the Vidmaster Challenge, a series of skill challenges hidden at the end of Marathon Infinity.

The Pfhor also utilize "Conditioned Ranks", or enslaved soldiers, who are forced to fight for the empire. Conquered races make up the majority of these conditioned ranks. The S'pht, the Drones (Wasp-like monsters with similar genetics to the Pfhor themselves) and the Drinniol ("Hulks") are the only conquered races encountered during play, while the Nahk are referred to as a now-extinct race that once attempted rebellion. The Nar are also mentioned as another race presently resisting Pfhor enslavement.

The Pfhor's solar system is eventually sacked by a fleet of Earth and S'pht ships in 2881 A.D.

Humans

Other than the player's character, the human characters in the game are all referred to as "BOBs" (which stands for "Born On Board"). They wear different-colored suits, but all have the same face. In the first game, the color of their suit represent their position aboard the Marathon. Green is worn by general crew members, red by engineering personnel, yellow by security perssonel, and blue by science and research team members. None of the humans are capable of defending themselves and all act the same. Though two levels in the game suggest that the player exterminate hostile forces while saving the humans (compliance with this suggestion is not enforced), they generally ignore the player (and occasionally announce in distress that "they're everywhere!").

In Marathon 2, the humans surviving the first battle with the Pfhor are put in stasis, and upon waking up, are given pistols to defend themselves. Throughout the years, many players have developed a pattern of intentionally killing the humans. If the player starts to visibly fire upon them, they will regard him as a traitor and fire back. In Marathon Infinity, there are humans who wear special suits for vacuum conditions, often called "VacBobs". Though they are protected from normally unsafe conditions, very few of them are seen in combat on either of the game's two vacuum levels. They differentiate from those humans not wearing environmental suits (though their color still indicates their work), not only in their voices (which are spoken over a radio because their faces are covered), but that they carry fusion guns. Bungie claimed to have designed their suits in a three-dimensional drawing program, then modified them to be 2.5-dimensional.

A few, called simulacrums (or "assimilated BOBs"), are actually living bombs created by the Pfhor; upon seeing the player, they will run directly towards him. They are almost indistinguishable from the genuine humans, except that in the game, they will always be wearing a green outfit, do not actually attack with weapons, have yellow blood (this can be revealed upon shooting one with an assault rifle bullet, which is not strong enough to kill), will shout ridiculous phrases that a normal person would not (in Marathon, they only said "Thank God it's you!", but in later games, things like "Kill me", "I'm out of ammo", or, most infamously, "Frog blast the vent core!"). There are theoretically (as the simulacrums are not humans, they do not need oxygen) vacuum-enabled versions, except they say different phrases. When close enough, the assimilated humans will explode and inflict severe damage upon those nearby. Certain levels task the player to destroy all the simulacrums without harming the identical normal humans, with the majority of the real officers wearing green. According to a terminal message, there are other differences between the real human and the bomb (due to obvious graphical limitations, they are not actually seen in the game). It is revealed that they have orbs for vision, not eyes, only two toes, a bomb implanted in the intestine, and lack of external genitalia. There are three thousand simulacrums according to the plotline.

Content creation

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A screenshot of Forge's Visual Mode feature

Forge is the name of the offical Bungie map editor used to create the levels of Marathon 2 and Marathon Infinity. Unlike modern first-person shooters, Marathon has a pseudo-3D engine that only creates the illusion of 3D by placing two-dimensional objects together. Each level consists of polygons linked together, each with its own textures, heights and lighting. If specified, a polygon can be a platform (one that can change its height), teleporter (on-level or off-level), hill or monster/light trigger. Polygons must have fewer than eight vertices and be convex. Truly three-dimensional structures such as bridges and balconies are not possible but can be created illusionally using polygons that overlap each other, a technique Bungie calls "5D space". Forge has a two-dimensional plane for drawing polygons and can be used to place objects such has player starting points, scenery, aliens, sounds or even annotations in polygons. It can merge several maps into a single file and permits levels with unique physics files. A major feature that accompanies the 2D editing mode is Visual Mode, a three-dimensional environment based on the rendering code of Marathon Infinity in which a it is possible to see the level as it is in the game and set textures, lights, heights, switches, terminals and pattern buffers.

Anvil is the sister program to Forge, and it is mainly utilized for the creation of Physics files, which hold the attributes of the player, monsters, weapons and other mechanics of play. In addition to this, Anvil also allows players to import and export custom graphics. Each image also comes with custom color palettes, which can be modified in Anvil to create different "classes" of an alien, for example. Another feature of Anvil is sound editing, where sounds can be imported or exported.

Legacy

The Marathon Trilogy has often been looked upon as one of the best games ever made for the Macintosh platform. It was released to much anticipation and received praise from reviewers. Marathon entered the market at a time when Doom, a PC game, was receiving much attention, and despite the fact that Marathon was technologically superior, it was on a large standard eclipsed. After Marathon Infinity was released in 1996, players began to create total conversions using Forge and Anvil. These may use custom maps, shapes, sounds or physics files and may or may not be set in the Marathon universe. Such conversions are still created to this day.

Bungie produced a compilation of all three games of the series called the Marathon Trilogy Box Set in 1997. The collection was on two disks. The collection was on two disks. The first contained all three Marathon games as well as Pathways Into Darkness, an earlier Bungie game and the spiritual prequel to the series. This disk also contains manuals for all three games, QuickTime 2.0 and other things necessary to run the game. There are beta versions of Marathon on this disk as well. The second disk of this contains thousands of user-created content, including maps, total conversions, shape and sound files, cheats, mapmaking tools, physics files, and other applications.

In 1998, QuickTime 3 was released, and the "QuickTime Musical Instruments" that permitted the playing of MIDI files was updated with some instruments changed. MIDI files do not contain any audio but instead provide instructions a synthesizer uses, which produces music. Since the background tracks in Marathon are MIDI files, many players who installed the new version quickly discovered that it drastically distorted some of the music, which was written for QuickTime 2. Tracks that were intended to be smooth and relaxing futuristic tracks sounded harsh and unrecognizable in some cases. Many feel that the music is now hideous and difficult to enjoy, and for that reason, many users reinstalled QuickTime 2, created modified music files, or did not play the game background music at all.

In the year 2000, Bungie was sold to Microsoft, who was interested in their Halo project. To thank Marathon fans for their devotion, they released the Marathon Infinity source code into public domain. Various projects have continued the legacy of the series by adding enhancements to Bungie's original code, such as Internet play, support for Lua and markup language and large resolutions. The most prominent and developed of these is called Aleph One (aleph is a number referring to all infinite numbers), which is compatible not only with Macintosh, but with Windows, Linux and even the Sega Dreamcast.

The Marathon Trilogy was finally released as abandonware in early 2005, along with Forge and Anvil.

Major total conversions

• Trojan
• Devil in a Blue Dress
• Excalibur: Morgana's Revenge
• Marathon EVIL
• Tempus Irae
• Marathon Rubicon
• Marathon Eternal
• Marathon Portal of Sigma
• Marathon RED

External links

• marathon.bungie.org: Marathon fan website
• The Trilogy Release: Site holding free and legal downloads of the Marathon Trilogy
• Marathon Open Source Project: Home of the Aleph One project
• Marathon's Story Site: Discussion of the storyline; includes a message board where the plot is actively discussed as of 2006
• Marathon Central: Marathon links directory
• The Battle Cat's Litterbox: Marathon map making tutorials and resources.
• Lh'owon Ar'kives: The most complete collection of Marathon maps and related files
• The Traxus Project: Wiki site devoted to the Marathon Trilogy in detail, as well as alternative scenarios utilizing the Aleph One game engine
• Marathon:Resurrection: A total conversion of Marathon to the Unreal engine